Filtration markers may have prognostic value independent of glomerular filtration rate

Glomerular Filtration of Creatinine: Validation of a Novel Index of Muscle Mass Among Older Adults

RATIONALE & OBJECTIVE

Low muscle mass is common among older adults and associated with poor prognosis. Quantifying muscle mass is challenging in routine clinical practice. We hypothesized that glomerular filtration of creatinine (GFcr) reflects muscle mass, and previously proposed estimated GFcr (eGFcr), as a practical index of muscle mass in older adults. This study investigated whether measured GFcr (mGFcr) and eGFcr are similarly associated with the direct measure of muscle mass, the thigh total muscle lean area (TTMLA).

STUDY DESIGN

Cross-sectional analysis of a community-based prospective cohort.

SETTING & PARTICIPANTS

A total of 794 older adults with measured glomerular filtration rate (mGFR) and TTMLA in the AGES-Reykjavik Study.

EXPOSURE

Measured GFcr, the product of serum creatinine (Scr) and mGFR obtained using plasma iohexol clearance and eGFcr, the product of Scr and estimated glomerular filtration rate using serum cystatin C (Scys).

OUTCOME

TTMLA measured using computed tomography.

ANALYTICAL APPROACH

Sex-specific Pearson's correlation and linear regression analyses using continuous and categorical mGFcr and eGFcr. Covariates included demographic, behavioral, and clinical variables, and comorbid conditions.

RESULTS

The mean age and mGFR were 80.3±4.0 (SD) years and 62.3±16.5 (SD) mL/min/1.73m2, respectively. The lowest sex-specific tertile of mGFcr, compared with the highest tertile, was associated with a 14.6 (95% CI, 11.5-17.6) cm2/1.73m2 lower TTMLA in men, and a 7.9 (95% CI, 5.5-10.2) cm2/1.73m2 lower TTMLA in women. Significant associations were observed between eGFcr and TTMLA. Correlations of eGFcr with TTMLA were generally as strong or stronger than correlations of alternative indices derived from Scr and Scys.

LIMITATIONS

Residual confounding by measured and unmeasured variables.

CONCLUSIONS

These findings support the validity of GFcr as an index of muscle mass among older adults and the use of eGFcr as a practical alternative to mGFcr in the clinical setting.

PLAIN-LANGUAGE SUMMARY

Low muscle mass is common among older adults and is associated with poor clinical outcomes. Quantifying muscle mass is challenging in routine clinical practice. We evaluated whether glomerular filtration of creatinine (GFcr) could serve as an index of muscle mass. We performed a cross-sectional study including 794 older adults who underwent computed tomography for thigh muscle lean area as a directly measured indicator of total body muscle mass. Significant positive associations between thigh muscle lean area and both measured GFcr (serum creatinine [Scr] ×measured glomerular filtration rate [GFR]) and estimated GFcr (Scr ×estimated GFR based on serum cystatin C [Scys]), a more practical index, were shown. These findings suggest the value of using eGFcr, a simply obtained novel index in the clinical setting, to assess muscle mass among older adults.

Comparative Prognostic Value of Glomerular Filtration Rate, Serum Cystatin C, Beta-2-Microglobulin and Albuminuria for Death and Chronic Kidney Disease Progression

AIMS

Serum creatinine and albuminuria are the core of most CKD prediction and progression risk models. Several biomarkers have been introduced to improve these results such as beta-2-microglobulin (B2M) and cystatin C (CysC). Nevertheless, few clinical comparisons of these biomarkers are available. We have compared serum B2M levels with albuminuria, CysC levels, and the CKD-EPI GFR equations.

DESIGNS AND METHODS

A sample of 434 patients were studied: 234 males and 200 females, the mean age was 58.3 ± 15.0 years, and 33.4% have diabetes mellitus. In all patients, plasma B2M, CysC, creatinine, and urinary albumin excretion were analyzed. EGFR was calculated using CKD-EPI equations for creatinine, CysC, and creatinine-CysC. The risk of death and CKD progression was evaluated using ROC curves and Cox proportional hazards survivorship models.

RESULTS

For mortality, the highest area under the curve (AUC) was for CysC (0.775, 0.676-0.875). The lowest sensitivity was shown by eGFR (creatinine) (0.298, 0.195-0.401, p < 0.001), eGFR (CysC) (0.216, 0.118-0.314, p < 0.001), and eGFR (creatinine + CysS) (0.218, 0.124-0.312, p < 0.001). For progression to advanced CKD, the highest AUC was for CysC (0.908, 0.862-0.954). The lowest sensitivity was shown by eGFR (creatinine) (0.184, 0.106-0.261, p < 0.001), eGFR (CysC) (0.095, 0.048-0.14, p < 0.001), and eGFR (creatinine+ CysC) (0.087, 0.040-0.134, p < 0.001). CysC, after age, was the second-best marker of life risk. Contrariwise, for CKD progression, CysC, and albuminuria were the best markers.

CONCLUSIONS

The best biomarker of mortality and risk of progression to CKD was CysC. Albuminuria and B2M were the next best options to be used. The lowest sensitivity was shown by estimated eGFR.

Association of Low Glomerular Filtration Rate With Adverse Outcomes at Older Age in a Large Population With Routinely Measured Cystatin C

BACKGROUND

The commonly accepted threshold of glomerular filtration rate (GFR) to define chronic kidney disease (CKD) is less than 60 mL/min/1.73 m2. This threshold is based partly on associations between estimated GFR (eGFR) and the frequency of adverse outcomes. The association is weaker in older adults, which has created disagreement about the appropriateness of the threshold for these persons. In addition, the studies measuring these associations included relatively few outcomes and estimated GFR on the basis of creatinine level (eGFRcr), which may be less accurate in older adults.

OBJECTIVE

To evaluate associations in older adults between eGFRcr versus eGFR based on creatinine and cystatin C levels (eGFRcr-cys) and 8 outcomes.

DESIGN

Population-based cohort study.

SETTING

Stockholm, Sweden, 2010 to 2019.

PARTICIPANTS

82 154 participants aged 65 years or older with outpatient creatinine and cystatin C testing.

MEASUREMENTS

Hazard ratios for all-cause mortality, cardiovascular mortality, and kidney failure with replacement therapy (KFRT); incidence rate ratios for recurrent hospitalizations, infection, myocardial infarction or stroke, heart failure, and acute kidney injury.

RESULTS

The associations between eGFRcr-cys and outcomes were monotonic, but most associations for eGFRcr were U-shaped. In addition, eGFRcr-cys was more strongly associated with outcomes than eGFRcr. For example, the adjusted hazard ratios for 60 versus 80 mL/min/1.73 m2 for all-cause mortality were 1.2 (95% CI, 1.1 to 1.3) for eGFRcr-cys and 1.0 (CI, 0.9 to 1.0) for eGFRcr, and for KFRT they were 2.6 (CI, 1.2 to 5.8) and 1.4 (CI, 0.7 to 2.8), respectively. Similar findings were observed in subgroups, including those with a urinary albumin-creatinine ratio below 30 mg/g.

LIMITATION

No GFR measurements.

CONCLUSION

Compared with low eGFRcr in older patients, low eGFRcr-cys was more strongly associated with adverse outcomes and the associations were more uniform.

PRIMARY FUNDING SOURCE

Swedish Research Council, National Institutes of Health, and Dutch Kidney Foundation.

Development of an adaptive clinical web-based prediction tool for kidney replacement therapy in children with chronic kidney disease

Clinicians need improved prediction models to estimate time to kidney replacement therapy (KRT) for children with chronic kidney disease (CKD). Here, we aimed to develop and validate a prediction tool based on common clinical variables for time to KRT in children using statistical learning methods and design a corresponding online calculator for clinical use. Among 890 children with CKD in the Chronic Kidney Disease in Children (CKiD) study, 172 variables related to sociodemographics, kidney/cardiovascular health, and therapy use, including longitudinal changes over one year were evaluated as candidate predictors in a random survival forest for time to KRT. An elementary model was specified with diagnosis, estimated glomerular filtration rate and proteinuria as predictors and then random survival forest identified nine additional candidate predictors for further evaluation. Best subset selection using these nine additional candidate predictors yielded an enriched model additionally based on blood pressure, change in estimated glomerular filtration rate over one year, anemia, albumin, chloride and bicarbonate. Four additional partially enriched models were constructed for clinical situations with incomplete data. Models performed well in cross-validation, and the elementary model was then externally validated using data from a European pediatric CKD cohort. A corresponding user-friendly online tool was developed for clinicians. Thus, our clinical prediction tool for time to KRT in children was developed in a large, representative pediatric CKD cohort with an exhaustive evaluation of potential predictors and supervised statistical learning methods. While our models performed well internally and externally, further external validation of enriched models is needed.

GFR estimated with creatinine rather than cystatin C is more reflective of the true risk of adverse outcomes with low GFR in kidney transplant recipients

BACKGROUND

Serum cystatin C-based estimated glomerular filtration rate (eGFRcys) generally associates with clinical outcomes better than serum creatinine-based eGFR (eGFRcr) despite similar precision in estimating measured GFR (mGFR). We sought to determine whether the risk of adverse outcomes with eGFRcr or eGFRcys was via GFR alone or also via non-GFR determinants among kidney transplant recipients.

METHODS

Consecutive adult kidney transplant recipients underwent a standardized GFR assessment during a routine follow-up clinic visit between 2011 and 2013. Patients were followed for graft failure or the composite outcome of cardiovascular (CV) events or mortality through 2020. The risk of these events by baseline mGFR, eGFRcr and eGFRcys was assessed unadjusted, adjusted for mGFR and adjusted for CV risk factors.

RESULTS

There were 1135 recipients with a mean baseline mGFR of 55.6, eGFRcr of 54.8 and eGFRcys of 46.8 ml/min/1.73 m2 and a median follow-up of 6 years. Each 10 ml/min/1.73 m2 decrease in mGFR, eGFRcr or eGFRcys associated with graft failure [hazard ratio (HR) 1.79, 1.68 and 2.07, respectively; P < .001 for all) and CV events or mortality outcome (HR 1.28, 1.19 and 1.43, respectively; P < .001 for all). After adjusting for mGFR, eGFRcys associated with graft failure (HR 1.57, P < .001) and CV events or mortality (HR 1.49, P < .001), but eGFRcr did not associate with either. After further adjusting for CV risk factors, risk of these outcomes with lower eGFRcys was attenuated.

CONCLUSION

eGFRcr better represents the true relationship between GFR and outcomes after kidney transplantation because it has less non-GFR residual association. Cystatin C is better interpreted as a nonspecific prognostic biomarker than is eGFR in the kidney transplant setting.

Impact of Chronic Kidney Disease on the Associations of Cardiovascular Biomarkers With Adverse Outcomes in Patients With Suspected or Known Coronary Artery Disease: The EXCEED-J Study

Background

The impact of chronic kidney disease (CKD) on the prognostic utility of cardiovascular biomarkers in high‐risk patients remains unclear.

Methods and Results

We performed a multicenter, prospective cohort study of 3255 patients with suspected or known coronary artery disease (CAD) to investigate whether CKD modifies the prognostic utility of cardiovascular biomarkers. Serum levels of cardiovascular and renal biomarkers, including soluble fms‐like tyrosine kinase‐1 (sFlt‐1), N‐terminal pro‐brain natriuretic peptide (NT‐proBNP), high‐sensitivity cardiac troponin‐I (hs‐cTnI), cystatin C, and placental growth factor, were measured in 1301 CKD and 1954 patients without CKD. The urine albumin to creatinine ratio (UACR) was measured in patients with CKD. The primary outcome was 3‐point MACE (3P‐MACE) defined as a composite of cardiovascular death, nonfatal myocardial infarction, and nonfatal stroke. The secondary outcomes were all‐cause death, cardiovascular death, and 5P‐MACE defined as a composite of 3P‐MACE, heart failure hospitalization, and coronary/peripheral artery revascularization. After adjustment for clinical confounders, sFlt‐1, NT‐proBNP, and hs‐cTnI, but not other biomarkers, were significantly associated with 3P‐MACE, all‐cause death, and cardiovascular death in the entire cohort and in patients without CKD. These associations were still significant in CKD only for NT‐proBNP and hs‐cTnI. NT‐proBNP and hs‐cTnI were also significantly associated with 5P‐MACE in CKD. The UACR was not significantly associated with any outcomes in CKD. NT‐proBNP and hs‐cTnI added incremental prognostic information for all outcomes to the model with potential clinical confounders in CKD.

Conclusions

NT‐proBNP and hs‐cTnI were the most powerful prognostic biomarkers in patients with suspected or known CAD and concomitant CKD.

Glomerular filtration and shrunken pore syndrome in children and adults

A major function of the kidney is to, by glomerular filtration, maintain the overall steady-state of 5-30 kDa proteins, many of which are signalling molecules. This function of the kidney has been overlooked, since predominantly low-molecular-mass substances <1 kDa have been used to measure or estimate glomerular filtration rate (GFR). The use of cystatin C (13 kDa) as a marker of GFR has allowed the discovery that the filtration of 5-30 kDa molecules can be selectively impaired defining the shrunken pore syndrome. The discovery, pathophysiology, morbidity (mainly cardiovascular manifestations) and mortality of this syndrome are described.

Potential relationship between eGFRcystatin C /eGFRcreatinine -ratio and glomerular basement membrane thickness in diabetic kidney disease

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease and renal replacement therapy worldwide. A pathophysiological hallmark of DKD is glomerular basal membrane (GBM) thickening, whereas this feature is absent in minimal change disease (MCD). According to fundamental transport physiological principles, a thicker GBM will impede the diffusion of middle-molecules such as cystatin C, potentially leading to a lower estimated GFR (eGFR) from cystatin C compared to that of creatinine. Here we test the hypothesis that thickening of the glomerular filter leads to an increased diffusion length, and lower clearance, of cystatin C. Twenty-nine patients with a kidney biopsy diagnosis of either DKD (n = 17) or MCD (n = 12) were retrospectively included in the study. GBM thickness was measured at 20 separate locations in the biopsy specimen and plasma levels of cystatin C and creatinine were retrieved from health records. A modified two-pore model was used to simulate the effects of a thicker GBM on glomerular water and solute transport. The mean age of the patients was 52 years, and 38% were women. The mean eGFRcystatin C /eGFRcreatinine -ratio was 74% in DKD compared to 98% in MCD (p < 0.001). Average GBM thickness was strongly inversely correlated to the eGFRcystatin C /eGFRcreatinine -ratio (Pearson's r = -0.61, p < 0.01). Two-pore modeling predicted a eGFRcystatin C /eGFRcreatinine -ratio of 78% in DKD. We provide clinical and theoretical evidence suggesting that thickening of the glomerular filter, increasing the diffusion length of cystatin C, lowers the eGFRcystatin C /eGFRcreatinine -ratio in DKD.

A New Panel-Estimated GFR, Including β2-Microglobulin and β-Trace Protein and Not Including Race, Developed in a Diverse Population

RATIONALE AND OBJECTIVE

Glomerular filtration rate (GFR) estimation based on creatinine and cystatin C (eGFRcr-cys) is more accurate than estimated GFR (eGFR) based on creatinine or cystatin C alone (eGFRcr or eGFRcys, respectively), but the inclusion of creatinine in eGFRcr-cys requires specification of a person's race. β2-Microglobulin (B2M) and β-trace protein (BTP) are alternative filtration markers that appear to be less influenced by race than creatinine is.

STUDY DESIGN

Study of diagnostic test accuracy.

SETTING AND PARTICIPANTS

Development in a pooled population of 7 studies with 5,017 participants with and without chronic kidney disease. External validation in a pooled population of 7 other studies with 2,245 participants.

TESTS COMPARED

Panel eGFR using B2M and BTP in addition to cystatin C (3-marker panel) or creatinine and cystatin C (4-marker panel) with and without age and sex or race.

OUTCOMES

GFR measured as the urinary clearance of iothalamate, plasma clearance of iohexol, or plasma clearance of [51Cr]EDTA.

RESULTS

Mean measured GFRs were 58.1 and 83.2 mL/min/1.73 m2, and the proportions of Black participants were 38.6% and 24.0%, in the development and validation populations, respectively. In development, addition of age and sex improved the performance of all equations compared with equations without age and sex, but addition of race did not further improve the performance. In validation, the 4-marker panels were more accurate than the 3-marker panels (P < 0.001). The 3-marker panel without race was more accurate than eGFRcys (percentage of estimates greater than 30% different from measured GFR [1 - P30] of 15.6% vs 17.4%; P = 0.01), and the 4-marker panel without race was as accurate as eGFRcr-cys (1 - P30 of 8.6% vs 9.4%; P = 0.2). Results were generally consistent across subgroups.

LIMITATIONS

No representation of participants with severe comorbid illness and from geographic areas outside of North America and Europe.

CONCLUSIONS

The 4-marker panel eGFR is as accurate as eGFRcr-cys without requiring specification of race. A more accurate race-free eGFR could be an important advance.

A Review of Specific Biomarkers of Chronic Renal Injury and Their Potential Application in Nonclinical Safety Assessment Studies

A host of novel renal biomarkers have been developed over the past few decades which have enhanced monitoring of renal disease and drug-induced kidney injury in both preclinical studies and in humans. Since chronic kidney disease (CKD) and acute kidney injury (AKI) share similar underlying mechanisms and the tubulointerstitial compartment has a functional role in the progression of CKD, urinary biomarkers of AKI may provide predictive information in chronic renal disease. Numerous studies have explored whether the recent AKI biomarkers could improve upon the standard clinical biomarkers, estimated glomerular filtration rate (eGFR), and urinary albumin to creatinine ratio, for predicting outcomes in CKD patients. This review is an introduction to alternative assays that can be utilized in chronic (>3 months duration) nonclinical safety studies to provide information on renal dysfunction and to demonstrate specific situations where these assays could be utilized in nonclinical drug development. Novel biomarkers such as symmetrical dimethyl arginine, dickkopf homolog 3, and cystatin C predict chronic renal injury in animals, act as surrogates for GFR, and may predict changes in GFR in patients over time, ultimately providing a bridge from preclinical to clinical renal monitoring.

Alternative kidney filtration markers and the risk of major macrovascular and microvascular events, and all-cause mortality in individuals with type 2 diabetes in the ADVANCE trial

BACKGROUND

Creatinine-based estimated glomerular filtration rate (eGFR) is biased in the setting of obesity and other conditions. Alternative kidney filtration markers may be useful in adults with diabetes, but few studies examined the associations with risk of clinical outcomes.

METHODS

In the Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation (ADVANCE) trial, we evaluated whether baseline levels and change in eGFR based on creatinine (Cr), cystatin c (Cys), β₂ -microglobulin (B2M), eGFR_Cr-Cys , and the average of three estimates (eGFR_Cr-Cys-B2M ) assessed in 7217 participants at baseline and a random sample of 640 participants at the 1-year visit are associated with clinical outcomes. We examined associations with major macrovascular and microvascular events together and separately and all-cause mortality using Cox regression models, adjusting for established risk factors.

RESULTS

Over a median follow-up of 5 years, 1313 major macrovascular (n = 748) and microvascular events (n = 637), and 743 deaths occurred. Lower levels of eGFR based on all filtration markers individually and combined were associated with 1.4 to 3.0 times higher risk of major macrovascular and microvascular events (combined and separately) and all-cause mortality. Per 30% decline in eGFR_Cys , eGFR _Cr-Cys , and eGFR_Cr-Cys-B2M were associated with a >2-fold higher risk of all clinical outcomes.

CONCLUSIONS

In adults with type 2 diabetes, baseline levels of eGFR based on alternative filtration markers and per 30% decline in eGFR_Cys , eGFR _Cr-Cys , and eGFR_Cr-Cys-B2M were associated with clinical outcomes. Measurement of alternative filtration markers, particularly B2M in adults with type 2 diabetes may be warranted.

Cystatin C and Muscle Mass in Patients With Heart Failure

BACKGROUND

The estimated glomerular filtration rate (eGFR) from cystatin C (eGFRcys) is often considered a more accurate method to assess GFR compared with an eGFR from creatinine (eGFRcr) in the setting of heart failure (HF) and sarcopenia, because cystatin C is hypothesized to be less affected by muscle mass than creatinine. We evaluated (1) the association of muscle mass with cystatin C, (2) the accuracy of eGFRcys, and (3) the association of eGFRcys with mortality given muscle mass.

METHODS AND RESULTS

We included 293 patients admitted with HF. Muscle mass was estimated with a validated creatinine excretion-based equation. Accuracy of eGFRcys and eGFRcr was compared with measured creatinine clearance. Cystatin C and creatinine were 31.7% and 59.9% higher per 14 kg higher muscle mass at multivariable analysis (both P < .001). At lower muscle mass, eGFRcys and eGFRcr overestimated the measured creatinine clearance. At higher muscle mass, eGFRcys underestimated the measured creatinine clearance, but eGFRcr did not. After adjusting for muscle mass, neither eGFRcys nor eGFRcr were associated with mortality (both P > .19).

CONCLUSIONS

Cystatin C levels were associated with muscle mass in patients with HF, which could potentially decrease the accuracy of eGFRcys. In HF where aberrations in body composition are common, eGFRcys, like eGFRcr, may not provide accurate GFR estimations and results should be interpreted cautiously.

Does Cystatin C have a role as metabolic surrogate in peritoneal dialysis beyond its association with residual renal function?

Introduction:

It has been suggested that cystatin C levels are modified by obesity and inflammation. Furthermore, cystatin C has been associated with cardiovascular events and mortality outcomes.

Aim:

To study the association of cystatin C with the metabolic profile and cardiovascular disease of peritoneal dialysis patients.

Methods:

Data collected included clinical, laboratorial, and multifrequency bioimpedance assessment of 52 stable peritoneal dialysis patients. Minimal residual renal function was defined as > 2mL/min/1.73m².

Results:

Serum cystatin C was not significantly associated with peritoneal or urinary cystatin C excretion. Negative correlation of cystatin C with normalized protein catabolic rate (rho -0.33, p = 0.02) and a trend towards positive correlation with relative body fat (rho 0.27, p = 0.05) were not independent from residual renal function. Cystatin C was not significantly associated with cardiovascular disease (p = 0.28), nor with glycated hemoglobin (p = 0.19) or c-reactive protein (p = 0.56). In the multivariate model, both age and diabetes were the strongest predictors of cardiovascular disease (odds ratio 1.09, p = 0.029 and odds ratio 29.95, p = 0.016, respectively), while relative body fat was negatively associated with cardiovascular disease (p = 0.038); neither cystatin C (p = 0.096) nor minimal residual renal function (p = 0.756) reached a significant association with cardiovascular disease.

Conclusions:

In this group of peritoneal dialysis patients, cystatin C did not correlate with the metabolic or inflammatory status, nor cardiovascular disease, after adjustment for residual renal function.

Association of Cystatin C with Metabolic Syndrome and Its Prognostic Performance in Non-ST-Segment Elevation Acute Coronary Syndrome with Preserved Renal Function

OBJECTIVE

The underlying mechanisms by which cystatin C affects cardiovascular disease (CVD) are not very clear. Metabolic syndrome (MetS) is a cluster of risk factors that increase the risk of CVD. Here, we aimed to investigate the association of cystatin C with metabolic syndrome and cardiovascular outcomes in non-ST-segment elevation acute coronary syndrome (NSTE-ACS) with preserved renal function.

METHODS

In total, 422 NSTE-ACS patients with preserved renal function were enrolled to examine the association of cystatin C with MetS. MetS was defined based on the NCEP-ATP-III guidelines. Major adverse cardiovascular events (MACEs) were also evaluated, which included cardiac death, nonfatal myocardial infarction (MI), target vessel revascularization (TVR), heart failure, and nonfatal stroke. All patients underwent a 12-month follow-up for MACEs after admission.

RESULTS

Cystatin C was significantly correlated with metabolic risk factors and inflammation markers. The prevalence of MetS and MACEs correlated with cystatin C levels. Cystatin C showed a strong diagnostic performance for cardiovascular risk factors and outcomes in ROC analysis. After adjustment for multiple risk factors, cystatin C level was independently associated with MetS (OR 2.299, 95% CI 1.251-4.225, and P = 0.007). During a 12-month follow-up, the patients with high cystatin C level and MetS had higher incidence of MACEs (Log-rank = 24.586, P < 0.001) and cardiac death (Log-rank = 9.890, P = 0.020) compared to the others. Multivariate Cox analysis indicated that cystatin C level was an independent predictor of MACEs (HR 2.609, 95% CI 1.295-5.257, and P = 0.007).

CONCLUSION

Cystatin C may be an independent predictor of metabolic syndrome and therefore valuable for management of NSTE-ACS patients. Further multicenter, large-scale studies are required to assess the implication of these results.

Creatinine- and cystatin C-based estimated glomerular filtration rate slopes for the prediction of kidney outcome: a comparative retrospective study

BACKGROUND

Many studies have evaluated the usefulness of creatinine- (eGFRcr) and cystatin C-based estimated glomerular filtration rate (eGFRcys) at specific time points in predicting renal outcome. This study compared the performance of both eGFR changing slopes in identifying patients at high risk of end-stage renal disease (ESRD).

METHODS

From 2012 to 2017, patients with more than three simultaneous measurements of serum creatinine and cystatin C for 1 year were identified. Rapid progression was defined as eGFR slope < - 5 mL/min/1.73 m²/year. The primary outcome was progression to ESRD.

RESULTS

Overall, 1323 patients were included. The baseline eGFRcr and eGFRcys were 39 (27-48) and 38 (27-50) mL/min/1.73 m², respectively. Over 2.9 years (range, 2.0-3.8 years) of follow-up, 134 subjects (10%) progressed to ESRD. Both the eGFRcr and eGFRcys slopes were associated with a higher risk of ESRD, independently of baseline eGFR (hazard ratio [HR] = 0.986 [0.982-0.991] and HR = 0.988 [0.983-0.993], respectively; all p <  0.001). The creatinine- and cystatin C-based rapid progressions were associated with increased risk of ESRD (HR = 2.22 [1.57-3.13], HR = 2.03 [1.44-2.86], respectively; all p <  0.001). In the subgroup analyses, the rapid progression group, defined on the basis of creatinine levels (n = 503), showed no association between the eGFRcys slope and ESRD risk (p = 0.31), whereas the eGFRcr slope contributed to further discriminating higher ESRD risk in the subjects with rapid progression based on eGFRcys slopes (n = 463; p = 0.003).

CONCLUSIONS

Both eGFR slopes were associated with future ESRD risk. The eGFRcr slope was comparable with the eGFRcys slope in predicting kidney outcome.

Cystatin C as a predictor of mortality in elderly patients with chronic kidney disease

BACKGROUND

The prevalence of chronic kidney disease (CKD) in the elderly is high. Serum cystatin C is an accurate marker of kidney function and it also has prognostic utility in CKD patients. The aim of our study was to determine the prediction of serum cystatin C and other markers of kidney function on long-term survival in elderly CKD patients.

METHODS

Fifty eight adult Caucasian patients, older than 65 years, without known malignancy, thyroid disease and/or not on steroid therapy were enrolled in the study. In each patient, 51CrEDTA clearance, serum creatinine, serum cystatin C, and estimated glomerular filtration rate using different equations were determined on the same day and patients were then followed for 11 years or until their death.

RESULTS

The means are as follows: 51CrEDTA clearance 53.3 ± 17.4 ml/min/1.73 m2, serum creatinine 1.62 ± 0.5 mg/dl, serum cystatin C 1.79 ± 0.5 mg/l, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation 40.1 ± 14 ml/min/1.73 m2, Berlin Initiative Study 2 (BIS2) equation 38.9 ± 10.7 ml/min/1.73 m2, full age spectrum (FAS) creatinine equation 43.8 ± 13.8 ml/min/1.73 m2, FAS cystatin C equation 40.1 ± 11.7 ml/min/1.73 m2. In the follow up period, 47 (81%) patients died. Cox regression analysis showed different hazard ratios (HRs) for death: for 51CrEDTA clearance HR 1.022 (95% CI 1.004-1.042; p = .015), serum creatinine HR 1.013 (95% CI 1.006-1.019; p = .001), serum cystatin C HR 2.028 (95% CI 1.267-3.241; p = .003), CKD-EPI creatinine equation HR 1.048 (95% CI 1.019-1.076; p = .001), BIS2 equation HR 1.055 (95% CI 1.021-1.088; p = .001), FAS creatinine equation HR 1.046 (95% CI 1.017-1.074; p = .001), FAS cystatin C equation HR 1.039 (95% CI 1.010-1.071; p = .009).

CONCLUSIONS

Our results showed the highest HR for serum cystatin C among kidney function markers for prediction of outcome in elderly CKD patients.

Cystatin C in adipose tissue and stimulation of its production by growth hormone and triiodothyronine in 3T3-L1 cells

Cystatin C (CysC) is a marker for estimation of glomerular filtration rate (GFR). CysC levels may depend not only on clearance/GFR but possibly also on changes in production. Our studies on tissue distribution of CysC protein in mice showed that adipose tissue expresses significant amounts of CysC, suggesting that adipocytes could contribute to circulating CysC levels in vivo. As growth hormone (GH) and triiodothyronine (T₃) increase both GFR and CysC (increased in acromegaly and hyperthyroidism) in vivo, we studied whether they could increase CysC production in 3T3-L1 adipocytes in vitro. CysC accumulated in culture media of 3T3-L1 adipocytes in a time-dependent fashion. GH and T₃ both (10 nmol/l) increased accumulation of CysC, to 373 ± 14 and 422 ± 20, respectively, vs 298 ± 10 ng per well over 4 days in controls. Thus, GH and T₃ enhance the production of CysC by adipocytes in vitro.

Upper Normal Serum Creatinine Concentrations as a Predictor for Chronic Kidney Disease: Analysis of 14 Years' Korean Genome and Epidemiology Study (KoGES)

Both serum creatinine (sCr) and estimated glomerular filtration rate (eGFR) have been used to assess kidney function in public health check-ups. However, when the sCr is within the normal levels but the eGFR is <60 mL/min/1.73 m², a dilemma arises, as the patients might progress to chronic kidney disease (CKD) after several years. We aimed to evaluate the association between normal sCr and the risk of incident CKD in the general population. For this, 9445 subjects from the Korean Genome and Epidemiology Study, with normal sCr and eGFR of >60 mL/min/1.73 m² were analyzed. The subjects were classified into quartiles based on sCr levels. The primary outcome was the development of eGFR <60 mL/min/1.73 m² on two consecutive measures. During a mean follow-up of 8.4 ± 4.3 years, 779 (8.2%) subjects developed eGFR <60 mL/min/1.73 m². The incidence of the development of eGFR <60 mL/min/1.73 m² was higher in the higher quartiles than in the lowest quartile. In multivariable Cox analysis, the highest quartile was associated with an increased risk for the development of eGFR <60 mL/min/1.73 m² (hazard ratio (HR), 4.71; 95% confidence interval (CI), 3.29⁻6.74 in females; HR, 12.77; 95% CI, 7.69⁻21.23 in males). In the receiver operating characteristic curve analysis, adding sCr to the traditional risk factors for CKD improved the accuracy of predicting the development of eGFR <60 mL/min/1.73 m² (area under the curve, 0.83 vs. 0.80 in females and 0.85 vs. 0.78 in males), and the cutoff value of sCr was 0.75 mg/dL and 0.78 mg/dL in females and males. Cautious interpretation is necessary when sCr is within the normal range, considering that the upper normal range of sCr has a higher risk of CKD development.

Cardiovascular risk assessment in prediabetic patients in a hypertensive population: The role of cystatin C

BACKGROUND

The aim of our study was to determine whether prediabetes increases cardiovascular (CV) risk compared to the non-prediabetic patients in our hypertensive population. Once this was achieved, the objective was to identify relevant CV prognostic features among prediabetic individuals.

METHODS

We included hypertensive 1652 patients. The primary outcome was a composite of incident CV events: cardiovascular death, stroke, heart failure and myocardial infarction. We performed a Cox proportional hazard regression to assess the CV risk of prediabetic patients compared to non-prediabetic and to produce a survival model in the prediabetic cohort.

RESULTS

The risk of developing a CV event was higher in the prediabetic cohort than in the non-prediabetic cohort, with a hazard ratio (HR) = 1.61, 95% CI 1.01-2.54, p = 0.04. Our Cox proportional hazard model selected age (HR = 1.04, 95% CI 1.02-1.07, p < 0.001) and cystatin C (HR = 2.4, 95% CI 1.26-4.22, p = 0.01) as the most relevant prognostic features in our prediabetic patients.

CONCLUSIONS

Prediabetes was associated with an increased risk of CV events, when compared with the non-prediabetic patients. Age and cystatin C were found as significant risk factors for CV events in the prediabetic cohort.

Can Serum Cystatin C predict long-term survival in cardiac surgery patients?

Renal dysfunction is a risk factor for morbidity and mortality in cardiac surgery patients. Serum Cystatin C (sCysC) is a well-recognized marker of early renal dysfunction but few reports evaluate its prognostic cardio-vascular role. The aim of the study is to consider the prognostic value of sCysC for cardiovascular mortality. Four hundred twenty-four cardiac-surgery patients (264 men and 160 women) were enrolled. At admission, all patients were tested for renal function and inflammatory status. Patients were subdivided in subgroups according to the values of the following variables: sCysC, serum Creatinine (sCrea), age, high sensitivity-C Reactive Protein, fibrinogen, surgical procedures and Kaplan-Meier cumulative survival curves were plotted. The primary end-point was cardiovascular mortality. In order to evaluate the simultaneous independent impact of all measured variables on survival we fitted a multivariate Cox-Proportional Hazard Model (CPHM). In Kaplan-Meier analysis 124 patients (29.4%) reached the end-point. In multivariate CPHM, the only significant predictors of mortality were sCysC (p<0.00001, risk ratio: 1.529, CI: 1.29-1.80) and age (p=0.039, risk ratio: 1.019, CI: 1.001-1.037). When replacing sCysC with sCrea, the only significant predictor of mortality was sCrea (p=0.0026; risk ratio 1.20; CI: 1.06-1.36). Increased levels of sCysC can be considered a useful biomarker of cardiovascular mortality in cardiac-surgery patients.

Therapeutic challenges in the mature patient

With the tremendous increase in the proportion of seniors in the global population, geriatric health care has become of greater interest and concern. Increased emphasis on geriatric medicine, along with the growth in the development of age-related skin disorders, has led to particular attention for geriatric, dermatology and dermatopharmacology. An aging population has brought many therapeutic challenges that we need to recognize and overcome by applying geropharmacologic principles. The purpose of this paper is to inform dermatologists of the age-related changes in the pharmacokinetics of common dermatologic drugs, their various interactions potentially occurring in the elderly, and the principles and evidence-based strategies for detection, management, and prevention to improve medication adherence. By implementing these principles and strategies, we can ensure the best and the safest treatment to promote the desired therapeutic outcome and improved quality of life for this fragile subpopulation.

Novel Filtration Markers for GFR Estimation

Creatinine-based glomerular filtration rate estimation (eGFR_cr) has been improved and refined since the 1970s through both the Modification of Diet in Renal Disease (MDRD) Study equation in 1999 and the CKD Epidemiology Collaboration (CKD-EPI) equation in 2009, with current clinical practice dependent primarily on eGFR for accurate assessment of GFR. However, researchers and clinicians have recognized limitations of relying on creatinine as the only filtration marker, which can lead to inaccurate GFR estimates in certain populations due to the influence of non-GFR determinants of serum or plasma creatinine. Therefore, recent literature has proposed incorporation of multiple serum or plasma filtration markers into GFR estimation to improve precision and accuracy and decrease the impact of non-GFR determinants for any individual biomarker. To this end, the CKD-EPI combined creatinine-cystatin C equation (eGFR_cr-cys) was developed in 2012 and demonstrated superior accuracy to equations relying on creatinine or cystatin C alone (eGFR_cr or eGFR_cys). Now, the focus has broadened to include additional novel filtration markers to further refine and improve GFR estimation. Beta-2-microglobulin (B2M) and beta-trace-protein (BTP) are two filtration markers with established assays that have been proposed as candidates for improving both GFR estimation and risk prediction. GFR estimating equations based on B2M and BTP have been developed and validated, with the CKD-EPI combined BTP-B2M equation (eGFR_BTP-B2M) demonstrating similar performance to eGFR and eGFR. Additionally, several studies have demonstrated that both B2M and BTP are associated with outcomes in CKD patients, including cardiovascular events, ESRD and mortality. This review will primarily focus on these two biomarkers, and will highlight efforts to identify additional candidate biomarkers through metabolomics-based approaches.

Pre-dialysis decline of measured glomerular filtration rate but not serum creatinine-based estimated glomerular filtration rate is a risk factor for mortality on dialysis

Background

Monitoring of renal function is important in patients with chronic kidney disease progressing towards end-stage renal failure, both for timing the start of renal replacement therapy and for determining the prognosis on dialysis. Thus far, studies on associations between estimated glomerular filtration rate (eGFR) measurements in the pre-dialysis stage and mortality on dialysis have shown no or even inverse relations, which may result from the poor validity of serum creatinine-based estimation equations for renal function in pre-dialysis patients. As decline in renal function may be better reflected by the mean of the measured creatinine and urea clearance based on 24-h urine collections (mGFR by C Cr-U ), we hypothesize that in patients with low kidney function, a fast mGFR decline is a risk factor for mortality on dialysis, in contrast to a fast eGFR decline.

Methods

For 197 individuals, included from the multicentre NECOSAD cohort, pre-dialysis annual decline of mGFR and eGFR was estimated with linear regression, and classified according to KDOQI as fast (>4 mL/min/1.73 m 2 /year) or slow (≤4 mL/min/1.73 m 2 /year). Cox regression was used to adjust for potential confounders.

Results

Patients with a fast mGFR decline had an increased risk of mortality on dialysis: crude hazard ratio (HR) 1.84 (95% confidence interval: 1.13-2.98), adjusted HR 1.94 (1.11-3.36). In contrast, no association was found between a fast eGFR decline in the pre-dialysis phase and mortality on dialysis: crude HR 1.20 (0.75-1.89), adjusted HR 1.14 (0.67-1.94).

Conclusions

This study demonstrates the importance of mGFR decline (by C Cr-U ) as opposed to eGFR decline in patients with low kidney function, and gives incentive for repeated mGFR measurements in patients on pre-dialysis care.

Superiority of Serum Cystatin C Over Creatinine in Prediction of Long-Term Prognosis at Discharge From ICU

OBJECTIVES

Renal outcomes after critical illness are seldom assessed despite strong correlation between chronic kidney disease and survival. Outside hospital, renal dysfunction is more strongly associated with mortality when assessed by serum cystatin C than by creatinine. The relationship between creatinine and longer term mortality might be particularly weak in survivors of critical illness.

DESIGN

Retrospective observational cohort study.

PATIENTS

In 3,077 adult ICU survivors, we compared ICU discharge cystatin C and creatinine and their association with 1-year mortality. Exclusions were death within 72 hours of ICU discharge, ICU stay less than 24 hours, and end-stage renal disease.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

During ICU admission, serum cystatin C and creatinine diverged, so that by ICU discharge, almost twice as many patients had glomerular filtration rate less than 60 mL/min/1.73 m when estimated from cystatin C compared with glomerular filtration rate estimated from creatinine, 44% versus 26%. In 743 patients without acute kidney injury, where ICU discharge renal function should reflect ongoing baseline, discharge glomerular filtration rate estimated from creatinine consistently overestimated follow-up glomerular filtration rate estimated from creatinine, whereas ICU discharge glomerular filtration rate estimated from cystatin C well matched follow-up chronic kidney disease status. By 1 year, 535 (17.4%) had died. In survival analysis adjusted for age, sex, and comorbidity, cystatin C was near-linearly associated with increased mortality, hazard ratio equals to 1.78 (95% CI, 1.46-2.18), 75th versus 25th centile. Conversely, creatinine demonstrated a J-shaped relationship with mortality, so that in the majority of patients, there was no significant association with survival, hazard ratio equals to 1.03 (0.87-1.2), 75th versus 25th centile. After adjustment for both creatinine and cystatin C levels, higher discharge creatinine was then associated with lower long-term mortality.

CONCLUSIONS

In contrast to creatinine, cystatin C consistently associated with long-term mortality, identifying patients at both high and low risk, and better correlated with follow-up renal function. Conversely, lower creatinine relative to cystatin C appeared to confer adverse prognosis, confounding creatinine interpretation in isolation. Cystatin C warrants further investigation as a more meaningful measure of renal function after critical illness.

Filtration Markers, Cardiovascular Disease, Mortality, and Kidney Outcomes in Stable Kidney Transplant Recipients: The FAVORIT Trial

Cystatin C and beta-2-microglobulin (B2M) are filtration markers associated with adverse outcomes in nontransplant populations, sometimes with stronger associations than for creatinine. We evaluated associations of estimated glomerular filtration rate from cystatin C (eGFR_cys ), B2M (eGFR_B2M ), and creatinine (eGFR_cr ) with cardiovascular outcomes, mortality, and kidney failure in stable kidney transplant recipients using a case-cohort study nested within the Folic Acid for Vascular Outcome Reduction in Transplantation (FAVORIT) Trial. A random subcohort was selected (N = 508; mean age 51.6 years, median transplant vintage 4 years, 38% women, 23.6% nonwhite race) with enrichment for cardiovascular events (N = 306; 54 within the subcohort), mortality (N = 208; 68 within the subcohort), and kidney failure (N = 208; 52 within the subcohort). Mean eGFR_cr , eGFR_cys , and eGFR_B2M were 46.0, 43.8, and 48.8 mL/min/1.73m² , respectively. After multivariable adjustment, hazard ratios for eGFR_cys and eGFR_B2M <30 versus 60+ were 2.02 (95% confidence interval [CI] 1.09-3.76; p = 0.03) and 2.56 (1.35-4.88; p = 0.004) for cardiovascular events; 3.92 (2.11-7.31) and 4.09 (2.21-7.54; both p < 0.001) for mortality; and 9.49 (4.28-21.00) and 15.53 (6.99-34.51; both p < 0.001) for kidney failure. Associations persisted with additional adjustment for baseline eGFR_cr . We conclude that cystatin C and B2M are strongly associated with cardiovascular events, mortality, and kidney failure in stable kidney transplant recipients.

Measured glomerular filtration rate does not improve prediction of mortality by cystatin C and creatinine

Background

Cystatin C may add explanatory power for associations with mortality in combination with other filtration markers, possibly indicating pathways other than glomerular filtration rate (GFR). However, this has not been firmly established since interpretation of associations independent of measured GFR (mGFR) is limited by potential multicollinearity between markers of GFR. The primary aim of this study was to assess associations between cystatin C and mortality, independent of mGFR. A secondary aim was to evaluate the utility of combining cystatin C and creatinine to predict mortality risk.

Methods

Cox regression was used to assess the associations of cystatin C and creatinine with mortality in 1157 individuals referred for assessment of plasma clearance of iohexol.

Results

Since cystatin C and creatinine are inversely related to mGFR, cystatin C - 1 and creatinine - 1 were used. After adjustment for mGFR, lower cystatin C - 1 (higher cystatin C concentration) and higher creatinine - 1 (lower creatinine concentration) were independently associated with increased mortality. When nested models were compared, avoiding the potential influence of multicollinearity, the independence of the associations was supported. Among models combining the markers of GFR, adjusted for demographic factors and comorbidity, cystatin C - 1 and creatinine - 1 combined explained the largest proportion of variance in associations with mortality risk ( R 2  = 0.61). Addition of mGFR did not improve the model.

Conclusions

Our results suggest that both creatinine and cystatin C have independent associations with mortality not explained entirely by mGFR and that mGFR does not offer a more precise mortality risk assessment than these endogenous filtration markers combined.

Relationships of Measured Iohexol GFR and Estimated GFR With CKD-Related Biomarkers in Children and Adolescents

BACKGROUND

2 valid and reliable estimated glomerular filtration rate (GFR) equations for the pediatric population have been developed from directly measured GFR data in the Chronic Kidney Disease in Children (CKiD) cohort: the full CKiD and bedside CKiD equations. Although adult GFR estimating equations replicate relationships of measured GFR with biomarkers, it is unclear whether similar patterns exist among children and adolescents with chronic kidney disease (CKD).

STUDY DESIGN

Prospective cohort study in children and adolescents.

SETTINGS & PARTICIPANTS

730 participants contributed 1,539 study visits.

PREDICTORS

Measured GFR by plasma iohexol disappearance (mGFR), estimated GFR by the full CKiD equation (eGFR_CKiDfull; based on serum creatinine, cystatin C, serum urea nitrogen, height, and sex), and estimated GFR by the bedside CKiD equation (eGFR_CKiDbed; calculated as 41.3 × height [m]/serum creatinine [mg/dL]) were predictors of CKD-related biomarkers. Deviations of mGFR from eGFR_CKiDfull and deviations of eGFR_CKiDfull from eGFR_CKiDbed from linear regressions (ie, residuals) were included in bivariate analyses.

OUTCOMES & MEASUREMENTS

CKD-related biomarkers included values for urine protein-creatinine ratio, blood hemoglobin, serum phosphate, bicarbonate, potassium, systolic and diastolic blood pressure z scores, and height z scores.

RESULTS

The median age of 730 participants with CKD was 12.5 years, with median mGFR, eGFR_CKiDfull, and eGFR_CKiDbed of 51.8, 54.0, and 53.2mL/min/1.73m², respectively. eGFR_CKiDfull demonstrated as strong or stronger associations with CKD-related biomarkers than mGFR; eGFR_CKiDbed associations were significantly attenuated (ie, closer to the null). Residual information in mGFR did not substantially increase explained variability. eGFR_CKiDbed estimated faster GFR decline relative to mGFR and eGFR_CKiDfull.

LIMITATIONS

Simple linear summaries of biomarkers may not capture nonlinear associations.

CONCLUSIONS

eGFR_CKiDfull closely approximated mGFR to describe relationships with CKD-severity indicators and progression in this pediatric CKD population. eGFR_CKiDbed offered similar inferences, but associations were attenuated and rate of progression was overestimated. The eGFR_CKiDfull equation from 2012 is preferred for pediatric research purposes.

Risk Factors for Heart Failure in Patients With Chronic Kidney Disease: The CRIC (Chronic Renal Insufficiency Cohort) Study

Background

Heart failure is common in patients with chronic kidney disease. We studied risk factors for incident heart failure among 3557 participants in the CRIC (Chronic Renal Insufficiency Cohort) Study.

Methods and Results

Kidney function was assessed by estimated glomerular filtration rate (eGFR) using serum creatinine, cystatin C, or both, and 24‐hour urine albumin excretion. During an average of 6.3 years of follow‐up, 452 participants developed incident heart failure. After adjustment for age, sex, race, and clinical site, hazard ratio (95% CI) for heart failure associated with 1 SD lower creatinine‐based eGFR was 1.67 (1.49, 1.89), 1 SD lower cystatin C‐based‐eGFR was 2.43 (2.10, 2.80), and 1 SD higher log‐albuminuria was 1.65 (1.53, 1.78), all P<0.001. When all 3 kidney function measures were simultaneously included in the model, lower cystatin C‐based eGFR and higher log‐albuminuria remained significantly and directly associated with incidence of heart failure. After adjusting for eGFR, albuminuria, and other traditional cardiovascular risk factors, anemia (1.37, 95% CI 1.09, 1.72, P=0.006), insulin resistance (1.16, 95% CI 1.04, 1.28, P=0.006), hemoglobin A1c (1.27, 95% CI 1.14, 1.41, P<0.001), interleukin‐6 (1.15, 95% CI 1.05, 1.25, P=0.002), and tumor necrosis factor‐α (1.10, 95% CI 1.00, 1.21, P=0.05) were all significantly and directly associated with incidence of heart failure.

Conclusions

Our study indicates that cystatin C‐based eGFR and albuminuria are better predictors for risk of heart failure compared to creatinine‐based eGFR. Furthermore, anemia, insulin resistance, inflammation, and poor glycemic control are independent risk factors for the development of heart failure among patients with chronic kidney disease.

Change in estimated glomerular filtration rate and outcomes in chronic kidney disease

PURPOSE OF REVIEW

Estimated glomerular filtration rate (eGFR) is important in the diagnosis and prognostication of chronic kidney disease (CKD). The current standards for CKD progression in clinical trials are kidney failure and the doubling of serum creatinine (∼57% decline in eGFR). These endpoints have limitations as they are only applicable to patients with later stages of CKD and often require large sample sizes to achieve adequate power.

RECENT FINDINGS

Lesser declines in eGFR (30% and 40%) have been evaluated as potential endpoints in recent studies. These endpoints are more common and show a strong association with the risk of end-stage renal disease and mortality. These findings have been shown to be consistent across different causes of CKD and for different interventions. A particular limitation of reduced thresholds is an elevated risk of type I errors in the presence of acute treatment effects, particularly with a 30% eGFR decline cut off.

SUMMARY

Surrogate endpoints for kidney failure and mortality are needed in clinical trials to allow for the reasonable management of timelines and resources, and the achievement of adequate sample sizes. Lesser eGFR decline thresholds should be considered to aid in the design and conduct of more randomized controlled trials in nephrology.

Filtration Markers as Predictors of ESRD and Mortality: Individual Participant Data Meta-Analysis

BACKGROUND AND OBJECTIVES

Serum β-trace protein (BTP) and β-2 microglobulin (B2M) are associated with risk of ESRD and death in the general population and in populations at high risk for these outcomes (GP/HR) and those with CKD, but results differ among studies.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed an individual patient-level meta-analysis including three GP/HR studies (n=17,903 participants) and three CKD studies (n=5415). We compared associations, risk prediction, and improvement in reclassification of eGFR using BTP (eGFRBTP) and B2M (eGFRB2M) alone and the average (eGFRavg) of eGFRBTP, eGFRB2M, creatinine (eGFRcr), and cystatin C (eGFRcys), to eGFRcr, eGFRcys, and their combination (eGFRcr-cys) for ESRD (2075 events) and death (7275 events).

RESULTS

Mean (SD) follow up times for ESRD and mortality for GP/HR and CKD studies were 13 (4), 6.2 (3.2), 14 (5), and 7.5 (3.9) years, respectively. Compared with eGFRcr, eGFRBTP and eGFRB2M improved risk associations and modestly improved prediction for ESRD and death even after adjustment for established risk factors. eGFRavg provided the most consistent improvement in associations and prediction across both outcomes and populations. Assessment of heterogeneity did not yield clinically relevant differences. For ESRD, addition of albuminuria substantially attenuated the improvement in risk prediction and risk classification with novel filtration markers. For mortality, addition of albuminuria did not affect the improvement in risk prediction with the use of novel markers, but lessened improvement in risk classification, especially for the CKD cohort.

CONCLUSIONS

These markers do not provide substantial additional prognostic information to eGFRcr and albuminuria, but may be appropriate in circumstances where eGFRcr is not accurate or albuminuria is not available. Educational efforts to increase measurement of albuminuria in clinical practice may be more cost-effective than measurement of BTP and B2M for improving prognostic information.

Cardiovascular Phenotypes in Children with CKD: The 4C Study

BACKGROUND AND OBJECTIVES

Cardiovascular disease is the most important comorbidity affecting long-term survival in children with CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Cardiovascular Comorbidity in Children with CKD Study is a multicenter, prospective, observational study in children ages 6-17 years old with initial GFR of 10-60 ml/min per 1.73 m2. The cardiovascular status is monitored annually, and subclinical cardiovascular disease is assessed by noninvasive measurements of surrogate markers, including the left ventricular mass index, carotid intima-media thickness, and central pulse wave velocity. We here report baseline data at study entry and an explorative analysis of variables associated with surrogate markers.

RESULTS

A total of 737 patients were screened from October of 2009 to August of 2011 in 55 centers in 12 European countries, and baseline data were analyzed in 688 patients. Sixty-four percent had congenital anomalies of the kidney and urinary tract; 26.1% of children had uncontrolled hypertension (24-hour ambulatory BP monitoring; n=545), and the prevalence increased from 24.4% in CKD stage 3 to 47.4% in CKD stage 5. The prevalence of left ventricular hypertrophy was higher with each CKD stage, from 10.6% in CKD stage 3a to 48% in CKD stage 5. Carotid intima-media thickness was elevated in 41.6%, with only 10.8% of patients displaying measurements below the 50th percentile. Pulse wave velocity was increased in 20.1%. The office systolic BP SD score was the single independent factor significantly associated with all surrogate markers of cardiovascular disease. The intermediate end point score (derived from the number of surrogate marker measurements >95th percentile) was independently associated with a diagnosis of congenital anomalies of the kidney and urinary tract, time since diagnosis of CKD, body mass index, office systolic BP, serum phosphorus, and the hemoglobin level.

CONCLUSIONS

The baseline data of this large pediatric cohort show that surrogate markers for cardiovascular disease are closely associated with systolic hypertension and stage of CKD.

Non-GFR Determinants of Low-Molecular-Weight Serum Protein Filtration Markers in CKD

BACKGROUND

Unlike the case with creatinine, conditions affecting the non-glomerular filtration rate (GFR) determinants of low-molecular-weight serum proteins, β-trace protein (BTP), β2-microglobulin (B2M), and cystatin C, are not well characterized.

STUDY DESIGN

Pooled cross-sectional analysis of 3 studies.

SETTING & PARTICIPANTS

3,156 persons with chronic kidney disease from the MDRD (Modification of Diet in Renal Disease) Study, AASK (African American Study of Kidney Disease and Hypertension), and CRIC (Chronic Renal Insufficiency Cohort) Study.

PREDICTORS

Demographic and clinical factors hypothesized to be associated with non-GFR determinants of the filtration markers, selected from literature review and physiologic and clinical considerations.

OUTCOMES

Serum creatinine, BTP, B2M, and cystatin C levels.

RESULTS

In multivariable-adjusted errors-in-variables regression models that included adjustment for measured GFR (mGFR) and mGFR measurement error, creatinine level had stronger associations with male sex, black race, and higher urine creatinine excretion than the other filtration markers. BTP was associated less strongly with age, similar in direction with sex, and opposite in direction with race than creatinine level. Like cystatin C, B2M level was associated less strongly with age, sex, and race than creatinine level. BTP, B2M, and cystatin C levels were associated more strongly than creatinine level with other factors, including urine protein excretion and weight for BTP, smoking and urine protein excretion for B2M, and smoking for cystatin C.

LIMITATIONS

Findings may not be generalizable to populations without chronic kidney disease, and residual confounding with GFR due to incomplete adjustment for GFR measurement error.

CONCLUSIONS

Like creatinine, serum levels of low-molecular-weight proteins are affected by conditions other than GFR. Knowledge of these conditions can aid the interpretation of GFR estimates and risk using these markers and guide the use of these filtration markers in developing GFR estimating equations.

Effect of glycemic index and carbohydrate intake on kidney function in healthy adults

BACKGROUND

Replacing carbohydrate with protein acutely increases glomerular filtration rate (GFR) but is associated with faster, long-term kidney disease progression. The effects of carbohydrate type (i.e. glycemic index, GI) on kidney function are unknown.

METHODS

We conducted an ancillary study of a randomized, crossover feeding trial in overweight/obese adults without diabetes or kidney disease (N = 163). Participants were fed each of four healthy, DASH-like diets for 5 weeks, separated by 2-week washout periods. Weight was kept constant. The four diets were: high GI (GI ≥65) with high %carb (58 % kcal) (reference diet), low GI (≤45) with low %carb (40 % kcal), low GI with high %carb; and high GI with low %carb. Plasma was collected at baseline and after each feeding period. Study outcomes were cystatin C, β2-microglobulin (β2M), and estimated GFR based on cystatin C (eGFRcys).

RESULTS

Mean (SD) age was 52 (11) years; 52 % were women; 50 % were black. At baseline, mean (SD) cystatin C, β2M, and eGFRcys were 0.8 (0.1) mg/L, 1.9 (0.4) mg/L, and 104 (16) mL/min/1.73 m(2). Compared to the high GI/high %carb diet, reducing GI, %carb, or both increased eGFRcys by 1.9 mL/min/1.73 m(2) (95 % CI: 1.1, 2.7; P < 0.001), 3.0 mL/min/1.73 m(2) (1.9, 4.0; P < 0.001), and 4.5 mL/min/1.73 m(2) (3.5, 5.4; P < 0.001), respectively. Increases in eGFRcys from reducing GI were significantly associated with increases in eGFRcys from reducing %carb (P < 0.001). Results for cystatin C and β2M reflected eGFRcys.

CONCLUSIONS

Reducing GI increased GFR. Reducing %carb by increasing calories from protein and fat, also increased GFR. Future studies on GI should examine the long-term effects of this increase in GFR on kidney injury markers and clinical outcomes.

TRIAL REGISTRATION

Clinical Trials.gov, number: NCT00608049 (first registered January 23, 2008).

Serum β-Trace Protein and β2-Microglobulin as Predictors of ESRD, Mortality, and Cardiovascular Disease in Adults With CKD in the Chronic Renal Insufficiency Cohort (CRIC) Study

BACKGROUND

Serum β-trace protein (BTP) and β2-microglobulin (B2M) are independently associated with end-stage renal disease (ESRD) and mortality in the general population and high-risk groups with diabetes or advanced chronic kidney disease (CKD). Less is known about their associations with outcomes and predictive ability in adults with moderate CKD.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

3,613 adults from the CRIC (Chronic Renal Insufficiency Cohort) Study (45% women; mean age, 57.9 years; 41.0% non-Hispanic black; 51.9% with diabetes).

PREDICTORS

BTP and B2M levels with a reciprocal transformation to reflect their associations with filtration, creatinine-based estimated glomerular filtration rate (eGFRcr), measured GFR, and a 4-marker composite score combining BTP, B2M, creatinine, and cystatin C levels. Predictors were standardized as z scores for comparisons across filtration markers.

OUTCOMES

ESRD, all-cause mortality, and new-onset cardiovascular disease.

RESULTS

During a 6-year median follow-up, 755 (21%) participants developed ESRD, 653 died, and 292 developed new-onset cardiovascular disease. BTP, B2M, and the 4-marker composite score were independent predictors of ESRD and all-cause mortality, and B2M and the 4-marker composite score of cardiovascular events, after multivariable adjustment. These associations were stronger than those observed for eGFRcr (P vs eGFRcr≤0.02). The 4-marker composite score led to improvements in C statistic and 2.5-year risk reclassification beyond eGFRcr for all outcomes.

LIMITATIONS

Filtration markers measured at one time point; measured GFR available in subset of cohort.

CONCLUSIONS

BTP and B2M levels may contribute additional risk information beyond eGFRcr, and the use of multiple markers may improve risk prediction beyond this well-established marker of kidney function among persons with moderate CKD.

Racial Disparities in Creatinine-based Kidney Function Estimates Among HIV-infected Adults

OBJECTIVE

The aim of our study was to investigate whether current eGFR equations in clinical use might systematically over-estimate the kidney function, and thus misclassify CKD status, of Black Americans with HIV. Specifically, we evaluated the impact of removing the race coefficient from the MDRD and CKD-EPI equations on comparisons between Black and White HIV-infected veterans related to: 1) the prevalence of reduced eGFR; 2) the distribution of eGFR values; and 3) the relationship between eGFR and all-cause mortality.

DESIGN

Retrospective cohort study.

SETTING

The Department of Veterans Affairs (VA) HIV Clinical Case Registry (CCR), which actively monitors all HIV-infected persons receiving care in the VA nationally.

PATIENT/PARTICIPANTS

21,905 treatment-naïve HIV-infected veterans.

MAIN OUTCOME MEASURES

Estimated glomerular filtration rate (eGFR) using the abbreviated Modification of Diet in Renal Disease (MDRD) formula with and without (MDRD-RCR) the race coefficient and all-cause mortality.

RESULTS

Persons with eGFR <45 mL/min/1.73m(2) had a higher risk of death compared with those with eGFR >80 mL/min/1.73m(2) among both Blacks (HR=2.8, 95%CI: 2.4-3.3) and Whites (HR=1.9, 95%CI: 1.4-2.6), but the association appeared to be stronger in Blacks (P=.038, test for interaction). Blacks with eGFR 45-60 mL/min/1.73m(2) also had a higher risk of death (HR=1.7, 95%CI: 1.4-2.1) but Whites did not (HR=.86, 95%CI: .67-1.10; test for interaction: P<.0001). Racial differences were substantially attenuated when eGFR was re-calculated without the race coefficient.

CONCLUSIONS

Our findings suggest that clinicians may want to consider estimating glomerular filtration rate without the race coefficient in Blacks with HIV.

Cystatin C as a biomarker for estimating glomerular filtration rate

PURPOSE OF REVIEW

Glomerular filtration rate (GFR) is rarely measured in clinical practice because of the complexity of the measurement. As such, kidney function is typically estimated using validated study equations, which use readily available data including age, sex, race, and serum creatinine as filtration marker. Contemporary research suggests that cystatin C may be an improved alternative to creatinine for inclusion in GFR estimating equations. The purpose of this article is to evaluate the benefits and limitations of using cystatin C as a biomarker of filtration.

RECENT FINDINGS

Cystatin C has fewer non-GFR determinants, when compared with serum creatinine. Use of serum cystatin C avoids the limitations related to both diet and muscle mass that affect serum creatinine. Cystatin C may be more accurate than serum creatinine in estimating GFR, and is more strongly associated with all-cause mortality and cardiovascular events.

SUMMARY

Cystatin C has some advantages over serum creatinine in estimating GFR. The use of cystatin C as a confirmatory biomarker in deciding medication dosages or as a confirmatory test in patients with an uncertain diagnosis of chronic kidney disease may be beneficial.

Effects of Traumatic Amputation on β-Trace Protein and β2-Microglobulin Concentrations in Male Soldiers

BACKGROUND

Serum creatinine (SCr) levels are decreased following traumatic amputation, leading to the overestimation of glomerular filtration rate (GFR). β-Trace protein (BTP) and β2-microglobulin (B2M) strongly correlate with measured GFR and have not been studied following amputation. We hypothesized that BTP and B2M would be unaffected by traumatic amputation.

METHODS

We used the Department of Defense Serum Repository to compare pre- and post-traumatic amputation serum BTP and B2M levels in 33 male soldiers, via the N Latex BTP and B2M nephelometric assays (Siemens Diagnostics, Tarrytown, N.Y., USA). Osterkamp estimation using DEXA scan measurements was used to establish percent estimated body weight loss (%EBWL). Results were analyzed for small (3-5.9% EBWL), medium (6-13.5%), and large (>13.5%) amputation subgroups; and for a control group matched 1:1 to the 12 large amputation subjects. Paired Student's t test was used for comparisons.

RESULTS

Mean serum BTP levels were unchanged in controls, all amputees, and the small and medium amputation subgroups. BTP appeared to decrease following large %EBWL amputation (p = 0.05). Mean serum B2M levels were unchanged in controls, all amputees, and the small and medium amputation subgroups. B2M appeared to increase following large %EBWL amputation (p = 0.05).

CONCLUSIONS

BTP and B2M levels are less affected than SCr by amputation, and should be considered for future study of GFR estimation. BTP and B2M changes following large %EBWL amputation require validation and may offer insight into non-GFR BTP and B2M determinants as well as increased cardiovascular disease and mortality following amputation.

GFR Estimation Using β-Trace Protein and β2-Microglobulin in CKD

BACKGROUND

β-Trace protein (BTP) and β2-microglobulin (B2M) are novel glomerular filtration markers that have stronger associations with adverse outcomes than creatinine. Comparisons of BTP and B2M to creatinine and cystatin C are limited by the absence of rigorously developed glomerular filtration rate (GFR) estimating equations for the novel markers.

STUDY DESIGN

Study of diagnostic test accuracy.

SETTING & PARTICIPANTS

Pooled database of 3 populations with chronic kidney disease (CKD) with mean measured GFR of 48 mL/min/1.73 m2 (N=3,551; MDRD [Modification of Diet in Renal Disease] Study, AASK [African American Study of Kidney Disease and Hypertension], and CRIC [Chronic Renal Insufficiency Cohort] Study).

INDEX TESTS

GFR estimated using creatinine, cystatin C, BTP, or B2M level.

REFERENCE TEST

GFR measured as the urinary clearance of iothalamate.

RESULTS

For BTP and B2M, coefficients for age, sex, and race were smaller than for creatinine and were similar or smaller than for cystatin C. For B2M, coefficients for sex, age, and race were smaller than for creatinine and were similar (age and race) or smaller (sex) than for cystatin C. The final equations with BTP (BTP, age, and sex) or B2M (B2M alone) were less accurate than either the CKD-EPI (CKD Epidemiology Collaboration) creatinine or cystatin C equations. The combined BTP-B2M equation (BTP and B2M alone) had similar accuracy to the CKD-EPI creatinine or cystatin C equation. The average of the BTP-B2M equation and the CKD-EPI creatinine-cystatin C equation was not more accurate than the CKD-EPI creatinine-cystatin C equation.

LIMITATIONS

No external validation population, study population was restricted to CKD, few participants older than 65 years, or nonblack nonwhite race.

CONCLUSIONS

BTP and B2M are less influenced by age, sex, and race than creatinine and less influenced by race than cystatin C, but provide less accurate GFR estimates than the CKD-EPI creatinine and cystatin C equations. The CKD-EPI BTP and B2M equation provides a methodological advance for their study as filtration markers and in their associations with risk and adverse outcomes, but further study is required before clinical use.

Change in Measured GFR Versus eGFR and CKD Outcomes

Measured GFR (mGFR) has long been considered the gold standard measure of kidney function, but recent studies have shown that mGFR is not consistently superior to eGFR in explaining CKD-related comorbidities. The associations between longitudinal changes in mGFR versus eGFR and adverse outcomes have not been examined. We analyzed a subset of 942 participants with CKD in the Chronic Renal Insufficiency Cohort Study who had at least two mGFRs and two eGFRs determined concurrently by iothalamate and creatinine (eGFRcr) or cystatin C, respectively. We compared the associations between longitudinal changes in each measure of kidney function over 2 years and risks of ESRD, nonfatal cardiovascular events, and all-cause mortality using univariate Cox proportional hazards models. The associations for all outcomes except all-cause mortality associated most strongly with longitudinal decline in eGFRcr. Every 5-ml/min per 1.73 m(2) decline in eGFRcr over 2 years associated with 1.54 (95% confidence interval, 1.44 to 1.66; P<0.001) times higher risk of ESRD and 1.23 (95% confidence interval, 1.12 to 1.34; P<0.001) times higher risk for cardiovascular events. All-cause mortality did not associate with longitudinal decline in mGFR or eGFR. When analyzed by tertiles of renal function decline, mGFR did not outperform eGFRcr in the association with any outcome. In conclusion, compared with declines in eGFR, declines in mGFR over a 2-year period, analyzed either as a continuous variable or in tertiles, did not consistently show enhanced association with risk of ESRD, cardiovascular events, or death.

Serum cystatin C levels are associated with asymptomatic peripheral arterial disease in type 2 diabetes mellitus patients without overt nephropathy

AIMS

We investigated the association between serum cystatin C and asymptomatic peripheral artery disease (PAD) in type 2 diabetes mellitus patients with normal renal function or mild renal impairment and we compared cystatin C with albuminuria and estimated glomerular filtration rate (eGFR) for prediction of PAD.

METHODS

We enrolled 272 patients with type 2 diabetes. Patients were excluded if they had an eGFR<60mL/min per 1.73m(2), 24-h urine albumin (24h-uAlb)≥300mg/day, serum creatinine (Cr)>1.3mg/dL, or previous history of cardiovascular disease. PAD was defined as having an ankle brachial index (ABI)≤0.9.

RESULTS

Patients with PAD were more likely to have a lower eGFR and higher values of 24h-uAlb, cystatin C, and serum Cr than subjects without PAD. Cystatin C was independently associated with age, current smoking, HDL, eGFR, and PAD. Odds ratios (ORs) for PAD after adjustment for age, gender, smoking, and hypertension were 1.71 (95% CI, 1.02-2.85), 1.51 (95% CI, 0.93-2.44), and 0.78 (95% CI, 0.41-1.49) for a one standard deviation increase in cystatin C, 24h-uAlb, and eGFR, respectively.

CONCLUSIONS

Cystatin C was independently associated with PAD in type 2 diabetes mellitus patients without overt nephropathy.

Filtration markers as predictors of ESRD and mortality in Southwestern American Indians with type 2 diabetes

BACKGROUND

A growing number of serum filtration markers are associated with mortality and end-stage renal disease (ESRD) in adults. Whether β-trace protein (BTP) and β2-microglobulin (B2M) are associated with these outcomes in adults with type 2 diabetes is not known.

STUDY DESIGN

Longitudinal cohort study.

SETTING & PARTICIPANTS

250 Pima Indians with type 2 diabetes (69% women; mean age, 42 years; mean diabetes duration, 11 years).

PREDICTORS

Serum BTP, B2M, and glomerular filtration rate measured by iothalamate clearance (mGFR) or estimated using creatinine (eGFRcr) or cystatin C level (eGFRcys).

OUTCOMES & MEASUREMENTS

Incident ESRD and all-cause mortality through December 2013. HRs were reported per interquartile range decrease of the inverse of BTP and B2M (1/BTP and 1/B2M) using Cox regression. Improvement in risk prediction with the addition of BTP or B2M level to established markers (eGFRcys with mGFR or eGFRcr) was evaluated using C statistics, continuous net reclassification improvement, and relative integrated discrimination improvement (RIDI).

RESULTS

During a median follow-up of 14 years, 69 participants developed ESRD and 95 died. Both novel markers were associated with ESRD in multivariable models. BTP level remained statistically significant after further adjustment for mGFR (1/BTP, 1.53 [95% CI, 1.01-2.30]; 1/B2M, 1.54 [95% CI, 0.98-2.42]). B2M level was associated with mortality in multivariable models and after further adjustment for mGFR (HR, 2.12; 95% CI, 1.38-3.26). The addition of B2M level to established markers increased the C statistic for mortality but only weakly when assessed by either continuous net reclassification improvement or RIDI; none was improved for ESRD by the addition of these markers.

LIMITATIONS

Small sample size, single measurements of markers.

CONCLUSIONS

In Pima Indians with type 2 diabetes, BTP and, to a lesser extent, B2M levels were associated with ESRD. B2M level was associated with mortality after adjustment for traditional risk factors and established filtration markers. Further studies are warranted to confirm whether inclusion of B2M level in a multimarker approach leads to improved risk prediction for mortality in this population.

Comparison of Serum Cystatin C and Creatinine Level Changes for Prognosis of Patients After Peripheral Arterial Angiography

We compared changes in serum cystatin C (Cys C) and creatinine (sCr) levels for detecting contrast-induced acute kidney injury; 350 consecutive patients who underwent peripheral arterial angiography were prospectively enrolled. Serum Cys C and sCr levels were assayed at predefined time points after contrast-media exposure. During 1-year follow-up, major adverse events (MAEs) including all-cause mortality and dialysis were assessed. A sCr increase ≥25% was not associated with MAEs, whereas a serum Cys C increase ≥5% at 24 hours was associated with higher probability of MAEs ( P = .010). The independent predictors of 1-year MAEs were older age ( P = .004), lower prealbumin levels ( P = .022), and serum Cys C increase ≥5%. In patients who underwent peripheral angiography, a serum Cys C increase ≥5% was an independent predictor of 1-year MAEs.

β-Trace protein: a marker of GFR and other biological pathways

β-Trace protein (BTP), also known as lipocalin prostaglandin D2 synthase (L-PGDS; encoded by the PTGDS gene), is a low-molecular-weight glycoprotein and an emerging novel marker of glomerular filtration rate. BTP is an important constituent of cerebral spinal fluid and is found in much lower concentrations in blood. Its serum origin and renal handling remain poorly understood. Unlike serum creatinine, BTP is not physiologically inert. It possesses both ligand-binding and enzymatic properties. BTP catalyzes the conversion of prostaglandin H2 (PGH2) to PGD2. PGD2 is an eicosanoid involved in a variety of important physiologic processes, including platelet aggregation, vasodilation, inflammation, adipogenesis, and bone remodeling. Several studies now have documented BTP's strong association with glomerular filtration rate, end-stage renal disease, cardiovascular disease, and death in a variety of different patient populations. This review provides an overview of the biochemistry, physiology and metabolism, biological functions, and measurement of BTP; summarizes the evidence for BTP as a marker of both kidney function and cardiovascular disease; and then considers the interplay between its biological properties, serum concentration, and patient outcomes.