Assessing renal function from creatinine measurements in adults with chronic renal failure

Performance of Panel-Estimated GFR Among Hospitalized Older Adults

RATIONALE & OBJECTIVE

Older adults represent nearly half of all hospitalized patients and are vulnerable to inappropriate dosing of medications eliminated through the kidneys. However, few studies in this population have evaluated the performance of equations for estimating the glomerular filtration rate (GFR)-particularly those that incorporate multiple filtration markers.

STUDY DESIGN

Cross-sectional diagnostic test substudy of a randomized clinical trial.

SETTING & PARTICIPANTS

Adults≥65 years of age presenting to the emergency department of Copenhagen University Hospital Amager and Hvidovre in Hvidovre, Denmark, between October 2018 and April 2021.

TESTS COMPARED

Measured GFR (mGFR) determined using 99mTc-DTPA plasma clearance compared with estimated GFR (eGFR) calculated using 6 different equations based on creatinine; 3 based on creatinine and cystatin C combined; and 2 based on panels of markers including creatinine, cystatin C, β-trace protein (BTP) and/or β2-microglobulin (B2M).

OUTCOME

The performance of each eGFR equation compared with mGFR with respect to bias, relative bias, inaccuracy (1-P30), and root mean squared error (RMSE).

RESULTS

We assessed eGFR performance for 106 patients (58% female, median age 78.3 years, median mGFR 62.9mL/min/1.73m2). Among the creatinine-based equations, the 2009 CKD-EPIcr equation yielded the smallest relative bias (+4.2%). Among the creatinine-cystatin C combination equations, the 2021 CKD-EPIcomb equation yielded the smallest relative bias (-3.4%), inaccuracy (3.8%), and RMSE (0.139). Compared with the 2021 CKD-EPIcomb, the CKD-EPIpanel equation yielded a smaller RMSE (0.136) but larger relative bias (-4.0%) and inaccuracy (5.7%).

LIMITATIONS

Only White patients were included; only a subset of patients from the original clinical trial underwent GFR measurement; and filtration marker concentration can be affected by subclinical changes in volume status.

CONCLUSIONS

The 2009 CKD-EPIcr, 2021 CKD-EPIcomb, and CKD-EPIpanel equations performed best and notably outperformed their respective full-age spectrum equations. The addition of cystatin C to creatinine-based equations improved performance, while the addition of BTP and/or B2M yielded minimal improvement.

FUNDING

Grants from public sector industry (Amgros I/S) and government (Capital Region of Denmark).

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with registration number NCT03741283.

PLAIN-LANGUAGE SUMMARY

Inaccurate kidney function assessment can lead to medication errors, a common cause of hospitalization and early readmission among older adults. Several novel methods have been developed to estimate kidney function based on a panel of kidney function markers that can be measured from a single blood sample. We evaluated the accuracy of these new methods (relative to a gold standard method) among 106 hospitalized older adults. We found that kidney function estimates combining 2 markers (creatinine and cystatin C) were highly accurate and noticeably more accurate than estimates based on creatinine alone. Estimates incorporating additional markers such as β-trace protein and β2-microglobulin did not further improve accuracy.

Glomerular hyperfiltration in patients with severe trauma

BACKGROUND AND OBJECTIVE

Augmented renal clearance or glomerular hyperfiltration (GHF) can significantly affect the clinical outcomes of renally eliminated drugs by promoting subtherapeutic drug exposure. The aggression suffered in patients who suffer severe trauma is a predisposition to manifest GHF and the identification of these patients remains a clinical challenge. The main objective of this study was to describe the prevalence of GHF in a cohort of critically ill trauma patients.

MATERIALS AND METHODS

Prospective observational study of a cohort of adult patients admitted after suffering severe trauma or polytrauma in the Anesthesiology ICU of the University Hospital of Albacete (Spain). Creatinine clearance (ClCr) was calculated in a 4-h urine collection sample at 24, 72 and 168 h after admission applying the formula; CrCl: [Diuresis in ml (urine/4 h) × Creatinine in urine (mg/dl)] ÷ [240 (minutes) × Creatinine in plasma (mg/dl)]. A CrCl above 130 mL/min was considered GHF. The analyses were performed with the statistical software R version 4.0.4.

RESULTS

85 patients were included. The median age of the patients was 51 years (IQR 26), 78.82% male. 68 patients were male (78.82%). 75.29% of the patients were polytraumatized. 61 patients (71.76%) presented GHF at some point in the CrCl determination. At 24 h of admission, 56.34% of the patients presented GHF with a mean CrCl of 195.8 ml/min, 61.11% of the patients presented it at 72 h with a mean CrCl of /min and 56.52% presented GHF at 168 h of admission with a mean CrCl of 207 ml/min. A significant positive relationship (p = 0.07) was found between GHF manifested at 72 h and at 168 h. We observed a statistically significant relationship between this phenomenon with younger ages, lower ISS scores and lower plasma creatinines.

CONCLUSIONS

GHF are a common condition in critically ill patients admitted for severe trauma. We recommend the use of CrCl to assess renal function and make dosage adjustments. Studies are required to understand the clinical impact of these phenomena on drug elimination and to be able to establish the ideal dosage in those cases.

Impact of cardiac surgery associated acute kidney injury on 1-year major adverse kidney events

Background

The incidence of acute kidney injury following cardiac surgery (CSA-AKI) is up to 30%, and the risk of chronic kidney disease (CKD) has been found to be higher in these patients compared to the AKI-free population. The aim of our study was to assess the risk of major adverse kidney events (MAKE) [25% or greater decline in estimated glomerular filtration rate (eGFR), new hemodialysis, and death] after cardiac surgery in a Spanish cohort and to evaluate the utility of the score developed by Legouis D et al. (CSA-CKD score) in predicting the occurrence of MAKE.

Methods

This was a single-center retrospective study of patients who required cardiac surgery with cardiopulmonary bypass (CPB) during 2015, with a 1-year follow-up after the intervention. The inclusion criteria were patients over 18 years old who had undergone cardiac surgery [i.e., valve substitution (VS), coronary artery bypass graft (CABG), or a combination of both procedures].

Results

The number of patients with CKD (eGFR < 60 mL/min) increased from 74 (18.3%) to 97 (24%) within 1 year after surgery. The median eGFR declined from 85 to 82 mL/min in the non-CSA-AKI patient group and from 73 to 65 mL/min in those with CSA-AKI (p = 0.024). Fifty-eight patients (1.4%) presented with MAKE at the 1-year follow-up. Multivariate logistic regression analysis showed that the only variable associated with MAKE was CSA-AKI [odds ratio (OR) 2.386 (1.31-4.35), p = 0.004]. The median CSA-CKD score was higher in the MAKE cohort [3 (2-4) vs. 2 (1-3), p < 0.001], but discrimination was poor, with a receiver operating characteristic curve (AUC) value of 0.682 (0.611-0.754).

Conclusion

Any-stage CSA-AKI is associated with a risk of MAKE after 1 year. Further research into new measures that identify at-risk patients is needed so that appropriate patient follow-up can be carried out.

Predicting the Effect of Renal Function on Systemic Clearance: Is a simple scaling method sufficient?

PURPOSE

To employ a simple scaling method to predict systemic or oral clearance for drugs that are primarily renally cleared knowing the fraction eliminated in urine (f_e) and a patient's renal function relative to healthy controls (S_GFR).

METHODS

Observations evaluating drug clearance as a function of creatinine clearance for renally cleared drugs (f_e >0.3) were obtained from literature sources. The analysis comprised of 82 unique drugs from 124 studies including 31 drugs with replicate studies. A simple scaler for renal function was employed and compared to the linear regression of available data. For drugs in which replicate studies were available, the ability of the linear regression (Cl vs Cl_CR) from one pharmacokinetic study was used to predict observations from an assigned replicate and compared to the scaling approach.

RESULTS

For patients categorized as severe kidney disease (Cl_CR fixed at 20 ml/min), the scalar tended to over predict some observations, but 92% of the predictions were within 50 - 200% of the observed data. For drugs with available replicates, the scalar was as good or better in predicting the influence of Cl_CR on systemic clearance from a separate study when comparing against the linear regression approach.

CONCLUSION

A scaling approach to account for alterations in drug clearance appears to have its advantages and represents a simple and generalizable method for guiding dose adjustments in patients with decreased renal function for drugs that are renally cleared (f_e >0.3). In addition to its use in clinical practice, validation of this approach may have implications in facilitating more efficient drug development processes for designing dose-adjusted pharmacokinetic studies in patients with renal disease.

Impact of solute carrier transporter gene polymorphisms on serum creatinine concentrations in healthy volunteers

In this study, we investigated the impact of single nucleotide polymorphisms in solute carrier (SLC) transporters, that is, SLC22A7 c.1586 + 206A > G, SLC22A2 c.808G > T, SLC22A3 c.1233G > A, SLC47A1 c.922-158G > A, and SLC47A2 c.-130G > A, on serum creatinine (SCr) concentrations. This cross-sectional study included residents who participated as volunteers in a health promotion study. Lifestyle data, blood chemical analysis data, and SLC gene polymorphism information were collected from each participant. Univariate analyses were carried out to determine differences between groups and correlations in SCr. Stepwise multiple regression analysis was performed to confirm the independence of factors that were significantly different in the univariate analyses. In multiple regression analyses, muscle mass, serum cystatin C concentrations, body fat percentage, serum albumin concentrations, and SLC47A2 c.-130G/G had the highest contribution to SCr concentrations, in that order (standardized regression coefficients = .505, .332, -.234, .123, and .084, respectively). The final model explained 72.2% of the variability in SCr concentrations. The SLC47A2 c.-130G > A polymorphism may affect creatinine dynamics in the proximal tubules. Further studies are needed to determine the effects of SLC transporter gene polymorphisms on SCr concentrations in patients with various diseases in real-world clinical settings.

Comparison of 24-hour urinary creatinine clearance and estimated glomerular filtration rate based on a panel of filtration markers in patients with chronic kidney disease

Diagnosis and management of chronic kidney disease (CKD) requires accurate assessment of glomerular filtration rate (GFR). In practice, GFR is typically estimated by equations based on creatinine concentration in blood, but creatinine is affected by non-GFR factors such as age and sex. Alternative filtration markers such as cystatin C, beta-trace protein (BTP), and beta-2 microglobulin (B2M) may be less dependent on age and sex, but equations combining these markers have not been investigated in patients with chronic kidney disease (CKD). In this cross-sectional study of 50 patients with CKD stage 3-4, we compared kidney function estimates based on creatinine, cystatin C, BTP, B2M, or a combination of markers. Compared to the creatinine/cystatin C combination equation, the panel equation yielded a mean difference of only 2.8 ml/min/1.73 m2 , indicating that switching to the panel equation would be unlikely to affect management.

Drugs Dosing in Geriatric Patients Depending on Kidney Function Estimated by MDRD and Cockroft-Gault Formulas

Introduction

According to the current data, regardless of the method used to estimate GFR, the differences between the obtained results should be insignificant and do not imply therapeutic decisions. The aim of this study was to analyze and compare the eGFR results with the estimated creatinine clearance score calculated according to the Cockroft-Gault equation, and to assess the significance of the difference between these two results.

Sample and Methods

A study group was constituted of 115 patients, of whom 76 were women and 39 men at the age range of 55–93 years, with a median of 79 years. The study analyzed differences in the assessment of kidney function by comparing the results of eGFR assessed by MDRD method obtained from the laboratory with the calculated values of creatinine clearance using the Cockroft-Gault formula, and examining the correlation between the difference D = eGFR -eClCr and BMI and body surface.

Results

In the entire group of patients (N = 115), the significant statistical difference was found between eGFR and eClCr. In the subgroup of patients (N = 45) with the lower baseline eGFR <60, there was no significant difference between eGFR and eClCr, while in the subgroup of patients with baseline eGFR ≥60 (N = 75), there was a significant difference between eGFR and eClCr. The study showed that based on the estimated GFR using both methods (C-G and MDRD), 29.2% and 32.4% of patients, respectively, were incorrectly assigned to given stage of chronic kidney disease.

Conclusion

Proper assessment of kidney function is very important in order to properly drugs dosing, especially to adjust the doses of drugs metabolized by the kidneys in order to avoid or minimize their nephrotoxic effects.

Measured and Estimated Glomerular Filtration Rate in the ICU: A Prospective Study

OBJECTIVES

To compare estimated glomerular filtration rate using classical static and kinetic equations with measured glomerular filtration rate assessed by plasma iohexol clearance in a mixed population of critical care patients.

PATIENTS

Unselected patients older than 18 and admitted to a general ICU.

DESIGN

Interventional prospective single center study.

INTERVENTION

Measurement of glomerular filtration rate by the plasma clearance of an IV single dose of iohexol and estimation of glomerular filtration rate with creatinine or cystatin C-based standard and kinetic equations as well as urinary creatinine clearance.

MEASUREMENTS AND MAIN RESULTS

Sixty-three patients were included with a median age of 66 years old. The median measured glomerular filtration rate was 51 mL/min/1.73 m (interquartile range, 19-85 mL/min/1.73 m). All used equations displayed significant biases, high errors, and poor accuracy when compared with measured glomerular filtration rate, overestimating renal function. The highest accuracy and lowest error were observed with cystatin C-based chronic kidney disease epidemiology collaboration equations. Both modification of diet in renal disease and Cockcroft-Gault equations displayed the lowest performance. Kinetic models did not improve performances, except in patients with unstable creatinine levels. Creatinine- but not cystatin C-based estimations largely derived over ICU stay, which appeared more related to sarcopenia than fluid balance. Finally, estimated glomerular filtration rate misclassified patients according to classical glomerular filtration rate categories in approximately half of the studied cases.

CONCLUSIONS

All known estimated glomerular filtration rate equations displayed high biases and unacceptable errors when compared with measured glomerular filtration rate in a mixed ICU population, with the lowest performance related to creatinine-based equations compared with cystatin C. In the ICU, we advocate for caution when using creatinine based estimated glomerular filtration rate equations. Drifting of serum creatinine levels over time should also be taken into consideration when assessing renal function in the ICU.

Dynamics of salivary markers of kidney functions in acute and chronic kidney diseases

Saliva can be used as an alternative diagnostic fluid enabling easy and non-invasive disease monitoring. Urea and creatinine can be measured in saliva and both were shown to be increased in renal failure. However, the dynamics of these markers during the development of kidney diseases is unknown. We aimed to describe the dynamics of salivary urea and creatinine in various animal models of acute kidney injury (AKI) and chronic kidney disease (CKD) and in patients with different stages AKI or CKD. Ninety Wistar rats underwent bilateral nephrectomy (BNX), ischemia–reperfusion injury (IRI) or glycerol-induced kidney injury to model AKI. CKD was modelled using 5/6 nephrectomy. In the clinical part 57 children aged 12.6 ± 4.9 years with AKI (n = 11) or CKD (n = 46) and 29 healthy controls (aged 10.2 ± 3.7 years) were enrolled. Saliva and blood samples were collected in both, animal experiments and the human study. In animal models of AKI, plasma urea and creatinine were higher than in controls. An increase of salivary urea and creatinine (twofold) was observed in BNX and IRI, but only after 12 h and 24 h, respectively. In glycerol nephropathy and 5/6 nephrectomy, salivary urea increased (by 100% and by 50%), while salivary creatinine did not change during the observation period. Salivary urea and creatinine were significantly higher in all patients compared to controls (threefold) and in both, AKI and CKD they were associated with the severity of renal failure. Plasma and salivary concentrations correlated only in children with renal failure (R = 0.72 for urea; R = 0.93 for creatinine), but not in controls (R = -0.007 for urea; R = 0.02 for creatinine). Our study indicates that during the development of renal impairment saliva could be used for non-invasive monitoring in higher stages of AKI or CKD, rather than for screening of early stages of kidney diseases.

Utility of serum beta-trace protein as a tool for estimating residual kidney function in peritoneal dialysis patients

BACKGROUND

Beta-trace protein (BTP) is a novel marker for residual kidney function (RKF) without need for urinary collection. We aimed to examine its utility as a tool for estimating RKF in incident peritoneal dialysis (PD) patients.

METHODS

This was a post hoc analysis of incident PD patients from the balANZ trial cohort. The outcomes evaluated were trends of serum BTP concentration with time, factors associated with change in BTP using mixed-effect multilevel linear regression and correlation of BTP with mean urinary urea and creatinine clearances (measured glomerular filtration rate (GFR)). Performances of two BTP-derived equations (Shafi-Eqn and Steubl-Eqn) to estimate GFR were evaluated by reporting bias (median difference between estimated and measured GFR), precision (interquartile range of median bias), accuracy (±2 mL/min of measured GFR) and P30 (percentage estimates within 30% of measured GFR) with confidence intervals (CIs) generated by bootstrapping 2000 replicates. The agreement between BTP-estimated GFR and measured GFR was also plotted graphically on Bland-Altman analysis.

RESULTS

The study included 161 PD patients. BTP concentration increased with dialysis vintage and was inversely correlated with measured GFR (r = -0.64). Larger increases in BTP were associated with longer PD vintage and higher dialysate glucose exposure. Biases of BTP-estimated GFRs (Shafi-Eqn and Steubl-Eqn) were 1.2 mL/min/1.73 m² (95% CI 1.0-1.3 mL/min/1.73 m²) and 0.4 mL/min/1.73 m² (95% CI 0.2-0.6 mL/min/1.73 m²), respectively. Both BTP-estimated GFRs had poor precision (3.2 mL/min/1.73 m² (95% CI 2.9-3.5 mL/min/1.73 m²) and 2.8 mL/min/1.73 m² (95% CI 2.5-3.2 mL/min/1.73 m²), respectively) and accuracy of estimates (55% (95% CI 52-60%) and 59% (95% CI 55-63%), respectively). The mean difference of BTP-estimated GFR (Shafi-Eqn and Steubl-Eqn) and measured GFR were -1.14 mL/min/1.73 m² and -0.42 mL/min/1.73 m², respectively, with large limit of agreement on Bland-Altman plot.

CONCLUSIONS

Serum BTP level was inversely related to RKF but neither BTP-estimated GFR equations were sufficiently accurate for routine use in PD patients.

Utility of Urine Biomarkers and Electrolytes for the Management of Heart Failure

PURPOSE OF REVIEW

To provide insight into the role of urine biomarkers and electrolytes for the management of heart failure.

RECENT FINDINGS

The age-dependent decrease in glomerular filtration rate due to loss of functional nephrons occurs at a faster pace in heart failure, potentially exacerbated by episodes of acute kidney injury. Urine biomarkers have not convincingly demonstrated to improve detection of irreversible renal damage and predict long-term renal trajectories, compared with serial creatinine measurements. Recent data show that natriuresis and diuretic response track poorly with glomerular filtration, but strongly with prognosis. Urine sodium concentration > 50-70 mmol/L was recently put forward through expert consensus as an adequate diuretic response. The value of urine biomarkers to detect structural renal damage in heart failure remains unsure and the latter is probably uncommon, especially over short-term follow-up. Urine electrolytes on the other hand predict diuretic response accurately and may allow better diuretic titration.

Tubular secretion of creatinine and kidney function: an observational study

BACKGROUND

Prior papers have been inconsistent regarding how much creatinine clearance (CrCl) overestimates glomerular filtration rate (GFR). A recent cross-sectional study suggested that measurement error alone could entirely account for the longstanding observation that CrCl/GFR ratio is larger when GFR is lower among patients with chronic kidney disease (CKD); but there have been no validation of this in other cohorts.

METHODS

To fill these gaps in knowledge regarding the relation between CrCl and GFR, we conducted cross-sectional and longitudinal analysis of the Modification of Diet in Renal Disease study (MDRD) and African American Study of Kidney Disease and Hypertension (AASK); and cross-sectional analysis of a clinical dataset from the Mayo Clinic of four different patient populations (CKD patients, kidney transplant recipients, post kidney donation subgroup and potential kidney donors). In the cross-sectional analyses (MDRD, AASK and Mayo Clinic cohort), we examined the relation between the CrCl/iothalamate GFR (iGFR) ratio at different categories of iGFR or different levels of CrCl. In the MDRD and AASK longitudinal analyses, we studied how the CrCl/iGFR ratio changed with those who had improvement in iGFR (CrCl) over time versus those who had worsening of iGFR (CrCl) over time.

RESULTS

Observed CrCl/iGFR ratios were generally on the lower end of the range reported in the literature for CKD (median 1.24 in MDRD, 1.13 in AASK and 1.25 in Mayo Clinic cohort). Among CKD patients in whom CrCl and iGFR were measured using different timed urine collections, CrCl/iGFR ratio were higher with lower iGFR categories but lower with lower CrCl categories. However, among CKD patients in whom CrCl and iGFR were measured using the same timed urine collections (which reduces dis-concordant measurement error), CrCl/iGFR ratio were higher with both lower iGFR categories and lower CrCl categories.

CONCLUSIONS

These data refute the recent suggestion that measurement error alone could entirely account for the longstanding observation that CrCl/GFR ratio increases as GFR decreases in CKD patients. They also highlight the lack of certainty in our knowledge with regard to how much CrCl actually overestimates GFR.

Atrial fibrillation in kidney transplant recipients: is there a place for the novel drugs?

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia of high clinical importance, occurring in 2% of the general population and in 19-24% in patients with chronic kidney disease. It is a well-known risk factor for cardiovascular morbidity and mortality. Kidney transplant recipients with a history of AF were associated with significantly higher rate of ischaemic strokes, graft failure and post-transplant mortality. AF occurs in over 7% of kidney transplant recipients in the first 3 years after transplantation and is associated with reduced graft and patient survival. The incidence of stroke in patients after kidney transplantation (KTx) is higher than the general population, but markedly lower than those on dialysis. Oral anticoagulation (OAC) therapy is recommended in AF patients at high risk of stroke. There are no randomized studies assessing OAC in patients after KTx and there are no specific recommendations and guidelines on therapeutic strategies in these patients. KTx recipients are a vulnerable population, exposed to variations in renal function, being at higher risk of bleeding and thrombotic complications, with possible interactions with immunosuppression. Surely, there is a place for novel oral anticoagulants (NOACs) in this group of patients as long as the summary of product characteristics is followed, as they are a valuable anticoagulation therapy. On one hand, they are at least as effective as warfarin; on the other hand NOACs are safer, especially when it comes to intracranial haemorrhages. However, NOACs seem to be underused in this population as they are excreted via kidney, may interact with immunosuppressive therapy and physicians need more experience and confidence in their administration. Percutaneous left atrial appendage occlusion procedure may also be considered as an opportunity for this group of patients, in particular in the presence of contraindications to anticoagulation.

Incident infection following acute kidney injury with recovery to baseline creatinine: A propensity score matched analysis

Background

Severe acute kidney injury (AKI) is associated with subsequent infection. Whether AKI followed by a return to baseline creatinine is associated with incident infection is unknown.

Objective

We hypothesized that risk of both short and long term infection would be higher among patients with AKI and return to baseline creatinine than in propensity score matched peers without AKI in the year following a non-infectious hospital admission.

Design

Retrospective, propensity score matched cohort study.

Participants

We identified 494 patients who were hospitalized between January 1, 1999 and December 31, 2009 and had AKI followed by return to baseline creatinine. These were propensity score matched to controls without AKI.

Main Measures

The predictor variable was AKI defined by International Classification of Diseases, Ninth Revision (ICD-9) codes and by the Kidney Disease Improving Global Outcomes definition, with return to baseline creatinine defined as a decrease in serum creatinine level to within 10% of the baseline value within 7 days of hospital discharge. The outcome variable was incident infection defined by ICD-9 code within 1 year of hospital discharge.

Results

AKI followed by return to baseline creatinine was associated with a 4.5-fold increased odds ratio for infection (odds ratio 4.53 [95% CI, 2.43–8.45]; p<0.0001) within 30 days following discharge. The association between AKI and subsequent infection remained significant at 31–60 days and 91 to 365 days but not during 61–90 days following discharge.

Conclusion

Among patients from an integrated health care delivery system, non-infectious AKI followed by return to baseline creatinine was associated with an increased odds ratio for infection in the year following discharge.

Plasma creatinine and amyotrophic lateral sclerosis prognosis: a systematic review and meta-analysis

Background: Plasma creatinine has been described as a prognostic biomarker for Amyotrophic Lateral Sclerosis (ALS), but with conflicting results in the literature. We performed a systematic review followed by a meta-analysis to address this question. Methods: We performed a systematic review of Pubmed, Embase and Cochrane databases and retrieved 14 distinct cohorts (19 studies) reporting results regarding the relationship between plasma creatinine and a clinical marker for ALS progression, notably ALSFRS (ALS Functional Rating Scale) and survival. Results: For baseline plasma creatinine, mortality risk was 28% lower when creatinine was higher than 88.4 µmol/L (hazard ratio (HR): 0.72; 95% confidence interval (CI): 0.58 to 0.88; p = 0.0003) and was 25% lower if creatinine was above versus below the median (HR: 0.75; 95% CI: 0.63 to 0.89; p = 0.0008). We found a significant positive correlation between plasma creatinine at baseline and functional score, and between creatinine decline and functional score decline (p < 0.0001 for both); but a negative correlation between plasma creatinine and functional score decline (p = 0.033). The overall quality of the studies was low mainly due to potential attrition bias, and several studies did not report analyzable results raising concern regarding a potential reporting bias. Conclusions: Plasma creatinine seems to be a promising prognostic biomarker for ALS. However, new studies with sound methodology and standardized criteria for the evaluation of ALS progression should be conducted to validate plasma creatinine as a clinical biomarker for ALS prognosis.

Optimal equation for estimation of glomerular filtration rate in autosomal dominant polycystic kidney disease: influence of tolvaptan

BACKGROUND

The reliability of various equations for estimating the GFR in ADPKD patients and the influence of tolvaptan on the resulting estimates have not been examined when GFR is calculated on the basis of inulin clearance.

METHODS

We obtained baseline and on-tolvaptan measured GFRs (mGFRs), calculated on the basis of inulin clearance, in 114 ADPKD, and these mGFRs were compared with eGFRs calculated according to four basic equations: the MDRD, CKD-EPI, and JSN-CKDI equations and the Cockcroft-Gault formula, as well as the influence of tolvaptan and of inclusion of cystatin C on accuracy of the results. Accuracy of each of the seven total equations was evaluated on the basis of the percentage of eGFR values within mGFR ± 30% (P₃₀).

RESULTS

mGFRs were distributed throughout CKD stages 1-5. Regardless of the CKD stage, P₃₀s of the MDRD, CKD-EPI, and JSN-CKDI equations did not differ significantly between baseline values and on-tolvaptan values. In CKD 1-2 patients, P₃₀ of the CKD-EPI equation was 100.0%, whether or not the patient was on-tolvaptan. In CKD 3-5 patients, P₃₀s of the MDRD, CKD-EPI, and JSN-CKDI equations were similar. For all four equations, regression coefficients and intercepts did not differ significantly between baseline and on-tolvaptan values, but accuracy of the Cockcroft-Gault formula was inferior to that of the other three equations. Incorporation of serum cystatin C reduced accuracy.

CONCLUSIONS

The CKD-EPI equation is most reliable, regardless of the severity of CKD. Tolvaptain intake has minimal influence and cystatin C incorporation does not improve accuracy.

Potential Role of Serum and Urinary Biomarkers in Diagnosis and Prognosis of Diabetic Nephropathy

PURPOSE OF REVIEW

Diabetic nephropathy (DN) is a progressive kidney disease caused by alterations in kidney architecture and function, and constitutes one of the leading causes of end-stage renal disease (ESRD). The purpose of this review is to summarize the state of the art of the DN-biomarker field with a focus on the new strategies that enhance the sensitivity of biomarkers to predict patients who will develop DN or are at risk of progressing to ESRD.

OBJECTIVE

In this review, we provide a description of the pathophysiology of DN and propose a panel of novel putative biomarkers associated with DN pathophysiology that have been increasingly investigated for diagnosis, to predict disease progression or to provide efficient personal treatment.

METHODS

We performed a review of the literature with PubMed and Google Scholar to collect baseline data about the pathophysiology of DN and biomarkers associated. We focused our research on new and emerging biomarkers of DN.

KEY FINDINGS

In this review, we summarized the critical signaling pathways and biological processes involved in DN and highlighted the pathogenic mediators of this disease. We next proposed a large review of the major advances that have been made in identifying new biomarkers which are more sensitive and reliable compared with currently used biomarkers. This includes information about emergent biomarkers such as functional noncoding RNAs, microRNAs, long noncoding RNAs, exosomes, and microparticles.

LIMITATIONS

Despite intensive strategies and constant investigation, no current single treatment has been able to reverse or at least mitigate the progression of DN, or reduce the morbidity and mortality associated with this disease. Major difficulties probably come from the renal disease being heterogeneous among the patients.

IMPLICATIONS

Expanding the proteomics screening, including oxidative stress and inflammatory markers, along with metabolomics approaches may further improve the prognostic value and help in identifying the patients with diabetes who are at high risk of developing kidney diseases.

Integrating Clinical Nutrition Practice Guidelines in Chronic Kidney Disease

Chronic kidney disease (CKD) is a permanent, progressive loss of kidney function characterized by a decline in glomerular filtration rate (GFR). Early identification of CKD risk factors provides an opportunity to prevent or delay the progression of kidney disease and decrease morbidity and mortality. There is increasing evidence to suggest that the adverse outcomes of CKD can be delayed or prevented by early detection and treatment. Current literature suggests that a low-protein, low-phosphorus diet may retard the progression of kidney disease. Other modifiable risk factors affecting CKD include proteinuria, hypertension, hyperglycemia, dyslipidemia, bone disease, anemia, and obesity. This discussion will review the current clinical nutrition guidelines for managing adult patients with CKD.

Measurement Error as Alternative Explanation for the Observation that CrCl/GFR Ratio is Higher at Lower GFR

BACKGROUND AND OBJECTIVES

Overestimation of GFR by urinary creatinine clearance (CrCl) at lower levels of GFR has long been attributed to enhanced creatinine secretion. However, this does not take into consideration the contribution of errors in measured GFR (and CrCl) due to short-term biologic variability or test imprecision.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We analyzed cross-sectional data among 1342 participants from the Chronic Renal Insufficiency Cohort study with baseline measurement of GFR by iothalamate clearance (iGFR) and CrCl by 24-hour urine collection. We examined the CrCl/iGFR ratio classified by categories of iGFR and also by categories of CrCl.

RESULTS

Overall, mean CrCl/iGFR ratio was 1.13. CrCl/iGFR ratio was higher at lower iGFR categories. In contrast, this ratio was lower at lower CrCl levels. We hypothesize these relationships could be due to measurement error, which is bolstered by replicating these trends in a simulation and modeling exercise in which there was no variation in the ratio of CrCl/iGFR with true kidney function but taking into account the effect of measurement error in both CrCl and iGFR (of magnitudes previously described in the literature). In our simulated data, the observed CrCl/iGFR ratio was higher at lower observed iGFR levels when patients were classified by categories of observed iGFR. When the same patients were classified by categories of observed CrCl, the observed CrCl/iGFR ratio was lower at lower observed CrCl levels.

CONCLUSIONS

The combined empirical and modeling results suggest that measurement errors (in both CrCl and iGFR) should be considered as an alternative explanation for the longstanding observation that the ratio of CrCl to iGFR gets larger as iGFR decreases.

Definition and Diagnosis of Acute Kidney Injury in Cirrhosis

BACKGROUND

Acute kidney injury (AKI) is a common complication of advanced cirrhosis. Type 1 hepatorenal syndrome is the best-known and most severe form of AKI, and it has a precise definition and a set of specific diagnostic criteria. More recently, it has become recognized that milder degrees of renal dysfunction also have a negative impact on patient outcome in various patient populations. Key Messages: Several definitions and criteria for staging the severity of AKI have been proposed, including the RIFLE (Risk, Injury, Failure, Loss of Function and End-Stage Renal Disease) group, the Acute Kidney Injury Network (AKIN), and the Kidney Disease: Improving Global Outcome (KDIGO) group. All of them incorporate some changes of serum creatinine and urine output in the definition and staging of AKI. The hepatology community has mostly embraced the AKIN diagnostic and staging criteria and has applied them in the prognostication of patients with advanced cirrhosis. However, the AKIN criteria have not been strictly applied in all studies on cirrhosis. This is partly related to the fact that changes in urine output are difficult to assess in advanced cirrhosis, and partly related to the difficulty in defining the baseline serum creatinine from which the change in serum creatinine is calculated. This has led to some confusion in the interpretation of results of the various studies on AKI in cirrhosis. More recently, some investigators have suggested incorporating the AKIN criteria with setting a lower limit of serum creatinine of 1.5 mg/dl in determining the diagnosis and prognosis of AKI in cirrhosis.

CONCLUSIONS

This is an ongoing debate as to how best to define AKI in cirrhosis. In the near future there should be prospective clinical trials that will clarify which diagnostic and staging criteria of AKI will best serve the cirrhotic population.

Comparison of equations with estimate renal function to predict serum vancomycin concentration in patients with spinal cord injury--does the use of cystatin C improve accuracy?

BACKGROUND

Vancomycin dose selection is challenging in the spinal cord injury (SCI) population because of the difficulty in accurately estimating the renal function. Creatinine-based equations have been shown to be unreliable in this patient population. Adjusted equations designed for patients with SCI have not been well studied. Cystatin C is an alternative marker of renal function that is less affected by muscle mass and may offer improvement in estimating renal function leading to improved initial dose selection.

OBJECTIVE

To compare the accuracy of serum creatinine- and serum cystatin C-based equations used in a pharmacokinetic (PK) model to predict steady-state serum vancomycin concentration in an SCI population. The rationale for this study is the need for an improved predictive model to guide initial vancomycin dose design before the availability of a measured steady-state serum concentration.

METHODS

Patients with SCI receiving vancomycin with measured serum creatinine, cystatin C, and steady-state serum vancomycin concentration were identified. Serum creatinine- and cystatin C-based equations to estimate renal function were substituted into a population-based PK model to predict steady state-serum vancomycin concentration. Predictions using each equation in the model were compared with the measured steady-state serum vancomycin concentration. Predictive performances using each equation in the PK model were compared.

RESULTS

The final study population included 37 patients with SCI. The Chronic Kidney Disease Epidemiology Collaboration cystatin C equation provided significantly less bias, greater precision, and superior accuracy when used in the PK model.

CONCLUSIONS

In the SCI population, the use of Chronic Kidney Disease Epidemiology Collaboration cystatin C equation may improve initial vancomycin dosing. Further study into this potential is encouraged.

Serum albumin, but not glycated albumin was a potent factor affecting the performance of GFR equation based on serum creatinine

BACKGROUND

Recently, Tsuda et al. reported that high HbA1C or high glycated albumin (GA) level is a major factor in overestimation of GFR by Japanese GFR equation based on serum creatinine (Eq-cr). They developed a modified equation of Eq-cr (M-Eq-cr) using GA or HbA1c. Therefore, effect of GA levels on the estimated GFR (eGFR) by Eq-cr was evaluated in Japanese subjects. We validated the accuracy of the modified equation using GA by Tsuda et al. (M-Eq-cr) and new equations that we developed in the present study.

METHODS

Seven hundred and fifteen Japanese subjects were included. GFR was measured by inulin renal clearance (Cin). The subjects were divided into two groups by upper limit of the GA reference range (GA-1: GA < 16.3 % and GA-2: GA > 16.4 %). Factors affecting the ratio of eGFR to Cin (eGFR/Cin) were evaluated using multivariate analysis. New equations based on creatinine and albumin (Eq-cr-alb) and based on creatinine, albumin and GA were developed from development dataset (382 subjects). Performances of the equations were validated in validation dataset (333 subjects).

RESULTS

Correlation coefficients between eGFR by Eq-cr and Cin were 0.839 and 0.914 in GA-1 and GA-2, respectively. Slopes (95 % confidential interval) of the regression lines with zero intercepts were 1.013 (0.991 to 1.036) and 0.997 (0.951 to 1.043), respectively. Both slopes were not significantly different from 1.0. Biases were -2.3 ± 19.0 and 0.2 ± 11.7 ml/min/1.73 m(2), respectively. Accuracy (p30; percentage of subjects within 30 % of Cin) (95 % CI) were 78 % (75, 81) and 71 % (62, 78), respectively. There was no significant difference in bias and accuracy between the two groups, indicating a reasonable accuracy of Eq-cr in GA-1 and GA-2. Multiple regression analysis showed that lower serum albumin and higher GA were associated with higher eGFR/Cin. Albumin was a more potent factor affecting eGFR/Cin than GA. M-Eq-cr significantly underestimated GFR and had significantly larger bias compared with Eq-cr in subjects with GA > 20 %, suggesting that the modification of Eq-cr using GA by Tsuda et al. was too much compensation in our subjects. Precisions of Eq-cr-alb were significantly better compared with Eq-cr.

CONCLUSION

Eq-cr has a reasonable accuracy in GA-1 and GA-2. Lower serum albumin and higher GA were significantly associated with higher eGFR/Cin. The former was a more potent factor affecting eGFR/Cin. Eq-cr-alb showed better performance compared with Eq-cr. M-Eq-cr using GA showed too much compensation and did not improve the accuracy of the equation in our subjects.

Performance of creatinine-based GFR estimating equations in solid-organ transplant recipients

BACKGROUND

Accurate assessment of kidney function is important for the management of solid-organ transplant recipients. In other clinical populations, glomerular filtration rate (GFR) most commonly is estimated using the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine or the 4-variable MDRD (Modification of Diet in Renal Disease) Study equation. The accuracy of these equations compared with other GFR estimating equations in transplant recipients has not been carefully studied.

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

Solid-organ transplant recipients longer than 6 months posttransplantation from 5 clinical populations (N=3,622, including recipients of kidney [53%], liver [35%], and other or multiple organs [12%]).

INDEX TEST

Estimated GFR (eGFR) using creatinine-based GFR estimating equations identified from a systematic review of the literature. Performance of the CKD-EPI creatinine and the MDRD Study equations was compared with alternative equations.

REFERENCE TEST

Measured GFR (mGFR) from urinary clearance of iothalamate or plasma clearance of iohexol.

MEASUREMENTS

Error (difference between mGFR and eGFR) expressed as P30 (proportion of absolute percent error <30%) and mean absolute error.

RESULTS

We identified 26 GFR estimating equations. Mean mGFR was 55.1±22.7 (SD) mL/min/1.73 m(2). P30 and mean absolute error for the CKD-EPI and the MDRD Study equations were 78.9% (99.6% CI, 76.9%-80.8%) for both and 10.6 (99.6% CI, 10.1-11.1) versus 11.0 (99.6% CI, 10.5-11.5) mL/min/1.73 m(2), respectively; these equations were more accurate than any of the alternative equations (P <0.001 for all pairwise comparisons for both measures). They performed better than or as well as the alternative equations in most subgroups defined by demographic and clinical characteristics, including type of transplanted organ.

LIMITATIONS

Study population included few nonwhites and people with solid-organ transplants other than liver and kidneys.

CONCLUSIONS

The CKD-EPI creatinine and the MDRD Study equations perform better than the alternative creatinine-based estimating equations in solid-organ transplant recipients. They can be used for clinical management.

Cross-Sectional Evaluation of Kidney Function in Hospitalized Patients: Estimated GFR Versus Renal Scintigraphy

<b><i>Background/Aims: </i></b>Accurate staging of chronic kidney disease (CKD) is very important. We tried to identify difference in GFR evaluation between CKD-EPI and Gates method with renal scintigraphy and which variables are associated with these differences. <b><i>Methods: </i></b>We retrospectively reviewed the records of 341 patients who underwent dynamic renal scintigraphy in the last 5 years. Patients were categorized according to KDIGO staging I to V, using the eGFR calculated with the CKD-EPI equation. Secondarily, we stratified patients according to treatment with renin-angiotensin system (RAS) inhibitors. <b><i>Results: </i></b>Gates method tends to underestimate GFR especially in CKD stage I (mean -22.2 ml/min) and II (mean -12.5 ml/min). The division in quartiles of ages showed an underestimation of GFR only in the first quartile of age (< 50 years old). Gates method underestimation of GFR was more pronounced in stage I patients treated with RAS inhibitors (mean -34.6 ml/min). The same occurs in stage II, even though to a lesser extent. <b><i>Conclusion: </i></b>The assessment of GFR by the Gates method must be carefully considered in the early stages of CKD, especially in younger patients. Moreover, the difference is more pronounced in patients treated with RAS inhibitors. Longitudinal studies will prove which method better predicts cardiovascular or renal events.

Improved measurement of the glomerular filtration rate from Tc-99m DTPA scintigraphy in patients following nephrectomy

OBJECTIVE

We aimed to improve Tc-99m DTPA glomerular filtration rate (GFR) scintigraphy (Gates' method) in a prospective study using Cr-51 EDTA GFR test as a gold standard.

METHODS

Fifty-seven Tc-99m DTPA GFR scintigrams in 45 subjects (male/female = 33:12, age = 45.9 ± 17.6 years, 14 healthy volunteers and 31 nephrectomised patients) were compared using Cr-51 EDTA GFR tests. Using the %renal uptake of Tc-99m DTPA and Cr-51 EDTA GFR, a revised equation for GFR was established through linear regression analysis.

RESULTS

The revised equation for improved GFR was GFR(mL/min) = (%renal uptake × 11.7773) - 0.7354. Gates' original GFRs (70.1 ± 20.5 mL/min/1.73 m(2)) were significantly lower than Cr-51 EDTA GFRs (97.0 ± 31.9 mL/min/1.73 m(2); P < 0.0001), but the improved GFRs (98.0 ± 26.3 mL/min/1.73 m(2)) were not different from (P = 0.7360) and had a significant correlation with (r = 0.73, P < 0.0001) the Cr-51 EDTA GFRs. The revised GFR equation effectively demonstrated perioperative GFR changes in kidneys that were operated on and the contralateral kidneys at 3 and 6 months post-partial nephrectomy (n = 25).

CONCLUSIONS

GFR measurement using Tc-99m DTPA scintigraphy could be significantly improved by a revised equation derived from the comparison with Cr-51 EDTA GFR.

KEY POINTS

• Measurement of glomerular filtration rate is difficult following nephrectomy. • Measurements can be significantly improved by new renal sctintigraphic methods. • This helps physicians to measure kidney function of patients following nephrectomy. • Management of renal tumour patients should become more effective.

Understanding kidney function assessment: the basics and advances

PURPOSE

Multiple kidney function assessment modalities are available, but their appropriateness is constantly questioned. This review provides practitioners with in-depth understanding of kidney function assessment methods, their clinical utility, and comparisons.

DATA SOURCES

PUBMED search was conducted by relevant subject headings.

CONCLUSIONS

Glomerular filtration rate (GFR) is the best indicator of kidney function. Exogenous compounds like inulin help measure GFR, but endogenous substances (like creatinine) are more convenient, although exhibiting greater variability. Cystatin C is advocated as a functional marker; its clinical significance is under study. Proteinuria adds value to GFR estimation. There are commonly used equations estimating GFR like the creatinine-based Cockcroft-Gault and the modification of diet in renal disease. The new creatinine-based Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation demonstrates higher accuracy of patient classification in earlier stages of disease. Recently, the Chronic Renal Insufficiency Cohort (CRIC) study has devised an equation combining serum creatinine and cystatin C in longitudinal modeling of kidney function.

IMPLICATIONS FOR PRACTICE

Current GFR estimation methods have limitations, and are useful for populations they have been tested in. Practitioners should be well informed on emerging equations that provide greater accuracy in CKD diagnosis; this would help implement appropriate prevention and intervention strategies.

25-hydroxyvitamin D deficiency is associated with an increased risk of metabolic syndrome in patients with non-diabetic chronic kidney disease

Background: Patients with chronic kidney disease (CKD) not requiring dialysis have a high prevalence of 25-hydroxyvitamin D (25(OH)D) deficiency but the relationship between 25(OH)D levels and metabolic syndrome is unknown in this population. Methods: This study analyzed stored plasma samples from 495 non-diabetic subjects with severe kidney disease, not yet on dialysis, who participated in the homocysteine in kidney and end stage renal disease study. Metabolic syndrome was defined as the presence of all three of the following: (1) Serum triglycerides ≥ 150 mg/dl or drug treatment for hypertriglyceridemia; (2) serum high density lipoprotein-cholesterol (HDL-C) < 50 mg/dl for women or < 40 mg/dl for men or drug treatment for dyslipidemia; and (3) blood pressure ≥ 130/85 mmHg or drug treatment for hypertension. Multivariate logistic regression models were used to evaluate the cross-sectional association between plasma 25(OH)D levels and metabolic syndrome. Results: The prevalence of metabolic syndrome increased as 25(OH)D levels declined, with the highest prevalence in participants with 25(OH)D levels < 20 ng/ml. Participants with 25(OH)D levels < 20 ng/ml had a significantly increased risk of metabolic syndrome compared to subjects with levels > 30 ng/ml after adjustment for multiple confounders (OR 2.25, 95% CI 1.25 – 4.07). Plasma 25(OH)D levels were inversely associated with diastolic blood pressure (R = –0.10, p = 0.029) and serum triglyceride levels (R = –0.14, p = 0.002). Conclusion: 25(OH)D deficiency is strongly associated with an increased risk of metabolic syndrome in non-diabetic patients with severe CKD not yet on dialysis, independent of cardiometabolic risk factors and other important regulators of mineral metabolism.

Comparison of estimating equations for the prediction of glomerular filtration rate in kidney donors before and after kidney donation

The aim of this study is to investigate the usefulness of the GFR-estimating equations to predict renal function in kidney donors before and after transplantation. We compared the performance of 24-hour-urine–based creatinine clearance (24 hr urine-CrCl), the Cockcroft-Gault formula (eGFR_CG), the Modification of Diet in Renal Disease equation (eGFR_MDRD), and the Chronic Kidney Disease Epidemiology Collaboration equation (eGFR_CKD-EPI) with technetium-diethylenetriaminepentaacetic acid (^99mTc-DTPA) clearance (mGFR) in 207 potential kidney donors and 108 uninephric donors. Before donation, eGFR_CKD-EPI showed minimal bias and did not show a significant difference from mGFR (P = 0.65, respectively) while 24 hr urine-CrCl and eGFR_MDRD significantly underestimated mGFR (P<0.001 for each). Precision and accuracy was highest in eGFR_CKD-EPI and this better performance was more dominant when renal function is higher than 90 mL·min⁻¹·1.73 m⁻². After kidney donation, eGFR_MDRD was superior to other equations in precision and accuracy in contrast to before donation. Within individual analysis, eGFR_MDRD showed better performance at post-donation compared to pre-donation, but eGFR_CKD-EPI and eGFR_CG showed inferior performance at post-donation. In conclusion, eGFR_CKD-EPI showed better performance compared to other equations before donation. In a uninephric donor, however, eGFR_MDRD is more appropriate for the estimation of renal function than eGFR_CKD-EPI.

C-reactive protein as a predictor of cardiovascular events in elderly patients with chronic kidney disease

BACKGROUND

Few studies have evaluated the relationship between high-sensitivity C-reactive protein (hs-CRP) and vascular events in the elderly with chronic kidney disease (CKD).

METHODS

The association of hs-CRP with vascular events was examined according to CKD status in 3,166 participants of the Intervention Project on Cerebrovascular Diseases and Dementia in the Community of Ebersberg, Bavaria (INVADE study). CKD was defined as a creatinine clearance <60 ml/min estimated by the Cockcroft-Gault formula. hs-CRP was used as a binary variable > or <2.1 mg/L (median value). Vascular events were defined as a composite of myocardial infarction, stroke and vascular death.

RESULTS

After 4 years of follow-up, 204 participants (6.4%) experienced a major cardiovascular event. High hs-CRP levels and CKD at baseline were associated with a greater risk of vascular events. Compared with patients with low hs-CRP and non-CKD, the adjusted hazard ratio (95% confidence interval) for vascular events was 1.42 (1.11-2.21) for low hs-CRP and CKD, 1.57 (1.21-2.34) for high hs-CRP and non-CKD and 1.93 (1.45-2.89) for high hs-CRP and CKD.

CONCLUSIONS

These results suggest that high hs-CRP levels provide prognostic information in patients with CKD.

Intravenous N-acetylcysteine for prevention of contrast-induced nephropathy: a meta-analysis of randomized, controlled trials

Background

Contrast-induced nephropathy (CIN) is one of the common causes of acute renal insufficiency after contrast procedures. Whether intravenous N-acetylcysteine (NAC) is beneficial for the prevention of contrast-induced nephropathy is uncertain. In this meta-analysis of randomized controlled trials, we aimed to assess the efficacy of intravenous NAC for preventing CIN after administration of intravenous contrast media.

Study Design

Relevant studies published up to September 2012 that investigated the efficacy of intravenous N-acetylcysteine for preventing CIN were collected from MEDLINE, OVID, EMBASE, Web of Science, Cochrane Central Register of Controlled Trials, and the conference proceedings from major cardiology and nephrology meetings. The primary outcome was CIN. Secondary outcomes included renal failure requiring dialysis, mortality, and length of hospitalization. Data were combined using random-effects models with the performance of standard tests to assess for heterogeneity and publication bias. Meta-regression analyses were also performed.

Results

Ten trials involving 1916 patients met our inclusion criteria. Trials varied in patient demographic characteristics, inclusion criteria, dosing regimens, and trial quality. The summary risk ratio for contrast-induced nephropathy was 0.68 (95% CI, 0.46 to 1.02), a nonsignificant trend towards benefit in patients treated with intravenous NAC. There was evidence of significant heterogeneity in NAC effect across studies (Q = 17.42, P = 0.04; I² = 48%). Meta-regression revealed no significant relation between the relative risk of CIN and identified differences in participant or study characteristics.

Conclusion

This meta-analysis showed that research on intravenous N-acetylcysteine and the incidence of CIN is too inconsistent at present to warrant a conclusion on efficacy. A large, well designed trial that incorporates the evaluation of clinically relevant outcomes in participants with different underlying risks of CIN is required to more adequately assess the role for intravenous NAC in CIN prevention.

CKD-EPI instead of MDRD for candidates to kidney donation

BACKGROUND

The determination of the glomerular filtration rate (GFR) is critical for the selection of a potential kidney donor. The complex and impractical techniques for the measurement of GFR have led to the development of equations to estimate GFR. Modification of diet in renal disease (MDRD) formula is the most widely used but its performance is poor because it systematically underestimates GFR above 60 mL/min. A new formula called the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) seems to overcome this limitation but needs to be tested in healthy potential kidney donors.

METHODS

From 2007 to 2011, a cross-sectional study was performed on 85 adults who were candidates for living-related kidney donation. GFR was measured by nonradiolabeled iothalamate clearance determined by high-performance liquid chromatography, and renal function was estimated by using CKD-EPI and MDRD equations. The overall performance of the equations was analyzed, and the estimation for GFR above 90 mL/min was studied by means of receiver operating characteristic curves.

RESULTS

The mean (SD) (range) of the measured GFR was 116 (24) (64-160) mL/min per 1.73 m(2), estimated GFR with CKD-EPI was 108 (22) (64-153) mL/min per 1.73 m(2), and MDRD was 99 (28) (46-157) mL/min per 1.73 m(2). CKD-EPI presented lower bias (3.3 vs. 10.2 mL/min/1.73 m(2)), higher precision [interquartile range (minimum value-maximum value), 25 (53-140) vs. 32 (43-161) ml/min] and higher accuracy (100% vs. 89%) compared with MDRD.

CONCLUSION

The CKD-EPI equation showed a higher performance than the MDRD equation in the GFR estimation of healthy population. CKD-EPI is applicable instead of MDRD, to subjects or candidates for kidney donation to avoid wrong GFR underestimates, which may lead to an inappropriate exclusion of candidates.

Effect of cobicistat on glomerular filtration rate in subjects with normal and impaired renal function

OBJECTIVE

This study evaluated the effect of cobicistat (COBI) on glomerular filtration rate in subjects with normal renal function (RF) or with mild/moderate renal impairment, by comparing creatinine clearance [estimated glomerular filtration rate (eGFR)] with actual GFR (aGFR) using iohexol, a probe drug excreted by glomerular filtration. COBI is a potent CYP3A inhibitor (pharmacoenhancer) currently in phase 3 testing with elvitegravir, atazanavir, and darunavir.

METHODS

Normal RF subjects received COBI 150 mg QD, ritonavir (RTV) 100 mg QD, or placebo for 7 days; subjects with mild/moderate renal impairment received COBI 150 mg QD. The eGFR and aGFR were measured on days 0, 7, and 14 and within-subject changes calculated relative to day 0. COBI and RTV pharmacokinetics were analyzed on day 7.

RESULTS

All 36 subjects in cohort 1 and 17 of 18 subjects in cohort 2 completed all study treatments. Study treatments were well tolerated. Small increases in serum creatinine with corresponding mean decreases in eGFR (∼10 mL/min or mL/min per 1.73 m) were observed on day 7 relative to day 0 in subjects receiving COBI (P < 0.05). The decreases were reversible on COBI discontinuation; mean eGFR values returned to baseline on day 14 (P > 0.05). No statistically significant changes in aGFR on days 7 or 14 relative to day 0 were seen with COBI (P > 0.05). No statistically significant decreases in aGFR or eGFR were observed with RTV or placebo.

CONCLUSIONS

COBI affects eGFR but not the actual GFR. The time to onset, magnitude, and time to resolution of changes in eGFR are consistent with altered proximal tubular secretion of creatinine through inhibition of drug transporters.

Estimating GFR among participants in the Chronic Renal Insufficiency Cohort (CRIC) Study

BACKGROUND

Glomerular filtration rate (GFR) is considered the best measure of kidney function, but repeated assessment is not feasible in most research studies.

STUDY DESIGN

Cross-sectional study of 1,433 participants in the Chronic Renal Insufficiency Cohort (CRIC) Study (ie, the GFR subcohort) to derive an internal GFR estimating equation using a split-sample approach.

SETTING & PARTICIPANTS

Adults from 7 US metropolitan areas with mild to moderate chronic kidney disease; 48% had diabetes and 37% were black.

INDEX TEST

CRIC GFR estimating equation.

REFERENCE TEST OR OUTCOME

Urinary (125)I-iothalamate clearance testing (measured GFR [mGFR]).

OTHER MEASUREMENTS

Laboratory measures, including serum creatinine and cystatin C, and anthropometrics.

RESULTS

In the validation data set, the model that included serum creatinine level, serum cystatin C level, age, sex, and race was the most parsimonious and similarly predictive of mGFR compared with a model additionally including bioelectrical impedance analysis phase angle, CRIC clinical center, and 24-hour urinary creatinine excretion. Specifically, root mean square errors for the separate models were 0.207 versus 0.202, respectively. Performance of the CRIC GFR estimating equation was most accurate for the subgroups of younger participants, men, nonblacks, non-Hispanics, those without diabetes, those with body mass index <30 kg/m(2), those with higher 24-hour urine creatinine excretion, those with lower high-sensitivity C-reactive protein levels, and those with higher mGFRs.

LIMITATIONS

Urinary clearance of (125)I-iothalamate is an imperfect measure of true GFR; cystatin C level is not standardized to certified reference material; lack of external validation; small sample sizes limit analyses of subgroup-specific predictors.

CONCLUSIONS

The CRIC GFR estimating equation predicts mGFR accurately in the CRIC cohort using serum creatinine and cystatin C levels, age, sex, and race. Its performance was best in younger and healthier participants.

Associations of plasma 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D concentrations with death and progression to maintenance dialysis in patients with advanced kidney disease

BACKGROUND

Low vitamin D concentrations are prevalent in patients with chronic kidney disease (CKD). We investigated the relationship between plasma 25-hydroxyvitamin D (25[OH]D) or 1,25-dihydroxyvitamin D (1,25[OH](2)D) concentrations with death, cardiovascular events, and dialysis therapy initiation in patients with advanced CKD.

STUDY DESIGN

The HOST (Homocysteinemia in Kidney and End Stage Renal Disease) Study was a randomized double-blind trial evaluating the effects of high doses of folic acid on death and long-term dialysis therapy initiation in patients with advanced CKD (stages 4 and 5 not yet on dialysis therapy). 25(OH)D and 1,25(OH)(2)D were measured in stored plasma samples obtained 3 months after trial initiation and evaluated at clinically defined cutoffs (<10, 10-30, and >30 ng/mL) and tertiles (<15, 15-22, and >22 pg/mL), respectively. Cox proportional hazard models were used to examine the association between vitamin D concentrations and clinical outcomes.

SETTING & PARTICIPANTS

1,099 patients with advanced CKD from 36 Veteran Affairs Medical Centers.

PREDICTORS

25(OH)D and 1,25(OH)(2)D concentrations.

OUTCOMES

Death, cardiovascular events, and time to initiation of long-term dialysis therapy.

RESULTS

After a median follow-up of 2.9 years, 41% (n = 453) died, whereas 56% (n = 615) initiated dialysis therapy. Mean 25(OH)D and 1,25(OH)(2)D concentrations were 21 ± 10 ng/mL and 20 ± 11 pg/mL, respectively. After adjustment for potential confounders, the lowest tertile of 1,25(OH)(2)D was associated with death (HR, 1.33; 95% CI, 1.01-1.74) and initiation of long-term dialysis therapy (HR, 1.78; 95% CI, 1.40-2.26) compared with the highest tertile. The association with death and initiation of dialysis therapy was moderately attenuated after adjustment for plasma fibroblast growth factor 23 (FGF-23) concentrations (HRs of lower tertiles of 1.20 [95% CI, 0.91-1.58] and 1.56 [95% CI, 1.23-1.99], respectively, compared with highest tertile). There was no association between 25(OH)D concentrations and outcomes.

LIMITATIONS

Participants were mostly men.

CONCLUSIONS

Low plasma 1,25(OH)(2)D concentrations are associated with death and initiation of long-term dialysis therapy in patients with advanced CKD. FGF-23 level may attentuate this relationship.

Association of complete recovery from acute kidney injury with incident CKD stage 3 and all-cause mortality

BACKGROUND

There is a gap of knowledge in the long-term outcomes of patients who have complete recovery of kidney function after an episode of acute kidney injury (AKI). We sought to determine whether complete recovery of kidney function after an episode of AKI is associated with the development of incident stage 3 chronic kidney disease (CKD) and mortality in patients with normal baseline kidney function.

DESIGN

Retrospective cohort study.

SETTING & PARTICIPANTS

3,809 patients from an integrated health care delivery system who had a hospitalization between January 1, 1999, and December 31, 2009, with follow-up through March 31, 2010.

PREDICTOR

AKI defined by International Classification of Diseases, Ninth Revision (ICD-9) codes and using the AKI Network (AKIN) definition, with complete recovery defined as a decrease in serum creatinine level to less than 1.10 times the baseline value.

OUTCOMES AND MEASUREMENTS

Incident stage 3 CKD persistent for 3 months and all-cause mortality.

RESULTS

After a median follow-up of 2.5 years, incident stage 3 CKD occurred in 15% and 3% of those with and without AKI, respectively, with an unadjusted HR of 5.93 (95% CI, 4.49-7.84) and HR of 3.82 (95% CI, 2.81-5.19) in propensity score-stratified analyses. Deaths occurred in 35% and 24% of those with and without AKI, respectively, with an unadjusted HR of 1.46 (95% CI, 1.27-1.68). In propensity score-stratified analyses, HR decreased to 1.08 (95% CI, 0.93-1.27).

LIMITATIONS

Measurements of albuminuria were not available.

CONCLUSIONS

Complete recovery of kidney function after an episode of AKI in patients with normal baseline kidney function is associated with increased risk of the development of incident stage 3 CKD, but not all-cause mortality.

The Influence of Body Size Descriptors on the Estimation of Kidney Function in Normal Weight, Overweight, Obese, and Morbidly Obese Adults

Background:

Dosing adjustments for patients with impaired kidney function are often based on estimated creatinine clearance (eCrCI) because measuring kidney (unction is not always possible for dose adjustment. However, there is no consensus on the body size descriptor that should be used in the estimation equations.

Objective:

To compare the use of alternative body size descriptors (ABSDs) on the performance of kidney function estimation equations compared with measured CrCI (mCrCI).

Methods:

We combined 2 data sources with mCrCI: a Food and Drug Administration clinical trial database that includes subjects with body mass index (BMI) less than 40 kg/m2 and published data from those 40 kg/m2 or more. The 3 parent equations (Cockcroft-Gault [CG], Modification of Diet in Renal Disease [MDRD], Chronic Kidney Disease-Epidemiology Collaboration [CKDEPI]), and 14 ABSD-modilied equations were compared with mCrCI for accuracy, bias, agreement, goodness of (it (R2). and prediction error. These equations were also compared across mCrCI and BMI strata.

Results:

Subjects (n = 590) were aged 19–80 years; 33.9% were female and BMI ranged from 17.2 to 95.6 kg/m2. Compared with mCrCI, the use of total weight in the CG equation yielded low accuracy (12.5%) and significant bias (–107 mL/min) in the morbidly obese group. In contrast, the use of lean body weights (BMI ≥40 kg/m2) and total ± adjusted weights (BMI <40 kg/m2) with the CG equation yielded higher accuracy, greater than or equal to 60.7% across all BMI strata, and was unbiased. Transforming the MDRD or CKDEPI equations with body surface area improved accuracy only at mCrCI of 30–80 mL/min and increased the overall prediction error.

Conclusions:

No kidney function equation was consistently accurate and unbiased across weight, mCrCI. and estimate ranges. The accuracy and over-estimation bias of the CG equation in obese subjects was improved through the selective use of total, adjusted, and lean body weight by BMI strata.

Racial differences in markers of mineral metabolism in advanced chronic kidney disease

BACKGROUND AND OBJECTIVES

This study examined differences in the concentration of markers of mineral metabolism across race in patients with advanced CKD not requiring dialysis and ESRD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Concentrations of 25-hydroxyvitamin D (25(OH)D), 1,25-dihydroxyvitamin D (1,25(OH)(2)D), intact parathyroid hormone (iPTH), and fibroblast growth factor 23 (FGF-23) were measured in stored plasma samples of 1497 patients with advanced CKD not yet on dialysis and ESRD who participated in the Homocysteine in Kidney and End Stage Renal Disease study. Linear regression models were used to examine the relationship between race and 25(OH)D, 1,25(OH)(2)D, iPTH, and FGF-23 concentrations.

RESULTS

Non-Hispanic white patients comprised 58% of the cohort, whereas non-Hispanic blacks comprised 42%. Median (interquartile range) FGF-23 concentrations were lower in blacks compared with whites with CKD (323 [181-655] versus 431 [232-1026] RU/ml; P<0.001) but not in ESRD. In adjusted linear regression models, blacks with CKD not requiring dialysis had significantly lower plasma FGF-23 concentrations (difference, -159; 95% confidence interval, -205 to -106; P<0.001) compared with whites, independent of plasma 25(OH)D, 1,25(OH)(2)D, and iPTH concentrations. This difference was not observed in the ESRD group. The magnitude of correlation for the relationships between 1,25(OH)(2)D with iPTH, FGF-23 with 1,25(OH)(2)D, and FGF-23 with iPTH were stronger among blacks than whites with CKD not requiring dialysis.

CONCLUSIONS

In advanced CKD not requiring dialysis, blacks have lower FGF-23 concentrations than whites. Blacks with CKD and ESRD have lower 25(OH)D and higher iPTH compared with whites, independent of FGF-23 concentrations.

Drug dosing consideration in patients with acute and chronic kidney disease-a clinical update from Kidney Disease: Improving Global Outcomes (KDIGO)

Drug dosage adjustment for patients with acute or chronic kidney disease is an accepted standard of practice. The challenge is how to accurately estimate a patient's kidney function in both acute and chronic kidney disease and determine the influence of renal replacement therapies on drug disposition. Kidney Disease: Improving Global Outcomes (KDIGO) held a conference to investigate these issues and propose recommendations for practitioners, researchers, and those involved in the drug development and regulatory arenas. The conference attendees discussed the major challenges facing drug dosage adjustment for patients with kidney disease. In particular, although glomerular filtration rate is the metric used to guide dose adjustment, kidney disease does affect nonrenal clearances, and this is not adequately considered in most pharmacokinetic studies. There are also inadequate studies in patients receiving all forms of renal replacement therapy and in the pediatric population. The conference generated 37 recommendations for clinical practice, 32 recommendations for future research directions, and 24 recommendations for regulatory agencies (US Food and Drug Administration and European Medicines Agency) to enhance the quality of pharmacokinetic and pharmacodynamic information available to clinicians. The KDIGO Conference highlighted the gaps and focused on crafting paths to the future that will stimulate research and improve the global outcomes of patients with acute and chronic kidney disease.

FGF-23 associates with death, cardiovascular events, and initiation of chronic dialysis

Concentrations of the phosphate-regulating hormone fibroblast growth factor-23 (FGF-23) are elevated in patients with chronic kidney disease (CKD), but whether higher plasma FGF-23 concentrations associate with all-cause mortality, cardiovascular events, or initiation of chronic dialysis is not completely understood. Here, we measured FGF-23 concentration in stored plasma samples from 1099 patients with advanced CKD who participated in The Homocysteine in Kidney and End Stage Renal Disease study. Mean serum phosphorus concentration was 4.3 mg/dl, median FGF-23 concentration was 392 RU/ml, and mean GFR was 18 ml/min/1.73 m(2). During a median follow-up of 2.9 yr, 453 (41%) patients died from any cause, 215 (20%) had a cardiovascular event, and 615 (56%) initiated chronic dialysis. Compared with the lowest quartile of FGF-23, each subsequent quartile associated with a progressively higher risk for death, adjusted for confounders (HR [95% CI] of 1.24 [0.91 to 1.69], 1.76 [1.28 to 2.44], and 2.17 [1.56 to 3.08] for the second through fourth quartiles, respectively). In addition, compared with the lowest quartile, the two highest quartiles of FGF-23 also associated with a significantly elevated risk for cardiovascular events and initiation of chronic dialysis. In conclusion, in advanced CKD, FGF-23 strongly and independently associates with all-cause mortality, cardiovascular events, and initiation of chronic dialysis.