Impact of creatinine calibration on performance of GFR estimating equations in a pooled individual patient database. Am J Kidney Dis. 2007;50:21-35. [PMID: 17591522 DOI: 10.1053/j.ajkd.2007.04.004]

External validation of the Revised Cardiac Risk Index and update of its renal variable to predict 30-day risk of major cardiac complications after non-cardiac surgery: rationale and plan for analyses of the VISION study

INTRODUCTION

The Revised Cardiac Risk Index (RCRI) is a popular classification system to estimate patients' risk of postoperative cardiac complications based on preoperative risk factors. Renal impairment, defined as serum creatinine >2.0 mg/dL (177 µmol/L), is a component of the RCRI. The estimated glomerular filtration rate has become accepted as a more accurate indicator of renal function. We will externally validate the RCRI in a modern cohort of patients undergoing non-cardiac surgery and update its renal component.

METHODS AND ANALYSIS

The Vascular Events in Non-cardiac Surgery Patients Cohort Evaluation (VISION) study is an international prospective cohort study. In this prespecified secondary analysis of VISION, we will test the risk estimation performance of the RCRI in ∼34 000 participants who underwent elective non-cardiac surgery between 2007 and 2013 from 29 hospitals in 15 countries. Using data from the first 20 000 eligible participants (the derivation set), we will derive an optimal threshold for dichotomising preoperative renal function quantified using the Chronic Kidney Disease Epidemiology Collaboration (CKD-Epi) glomerular filtration rate estimating equation in a manner that preserves the original structure of the RCRI. We will also develop a continuous risk estimating equation integrating age and CKD-Epi with existing RCRI risk factors. In the remaining (approximately) 14 000 participants, we will compare the risk estimation for cardiac complications of the original RCRI to this modified version. Cardiac complications will include 30-day non-fatal myocardial infarction, non-fatal cardiac arrest and death due to cardiac causes. We have examined an early sample to estimate the number of events and the distribution of predictors and missing data, but have not seen the validation data at the time of writing.

ETHICS AND DISSEMINATION

The research ethics board at each site approved the VISION protocol prior to recruitment. We will publish our results and make our models available online at http://www.perioperativerisk.com.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT00512109.

Chronic kidney disease and 10-year risk of cardiovascular death

BACKGROUND

In recent clinical guidelines, individuals with chronic kidney disease are considered to have a similar 10-year absolute risk of cardiovascular death as individuals with diabetes or established cardiovascular disease. There is limited evidence to support this claim.

METHODS

We investigated the 10-year risk for cardiovascular death in individuals with moderate or severe chronic kidney disease (glomerular filtration rate of 30-60 or <30 mL/min/1.73 m(2), respectively) in a cohort of primary care health check-ups in Stockholm, Sweden (n = 295,191, 46% women, 4290 cardiovascular deaths during 10 years follow-up). We also assessed the risk associated with diabetes or cardiovascular disease. The inclusion criteria, exposure, study outcome and follow-up period adhered strictly to the definitions of the European Society of Cardiology guidelines.

RESULTS

The absolute 10-year risk of cardiovascular death was 3.9% and 14.0% in individuals with moderate and severe chronic kidney disease, respectively, but was substantially lower in women and in younger individuals. The risk in individuals with prevalent diabetes and cardiovascular disease was approximately two and three times higher compared to the risk estimate for moderate chronic kidney disease (hazard ratio (HR) 4.1, 95% confidence interval (CI) 3.8-4.5 and HR 6.2, 95% CI 5.7-6.7 vs. HR 2.3 95% CI 2.0-2.6, respectively) while the risk for individuals with severe chronic kidney disease appeared more congruent to that of diabetes and cardiovascular disease (HR 5.5, 95% CI 3.3-8.9).

CONCLUSIONS

Although moderate chronic kidney disease is an independent predictor for an increased 10-year risk of cardiovascular death, only those with severe chronic kidney disease had similar risk to those with diabetes or cardiovascular disease.

Renal function assessment in atrial fibrillation: Usefulness of chronic kidney disease epidemiology collaboration vs re-expressed 4 variable modification of diet in renal disease

AIM: To compare the performance of the re-expressed Modification of Diet in Renal Disease equation vs the new Chronic Kidney Disease Epidemiology Collaboration equation in patients with non-valvular atrial fibrillation.

METHODS: We studied 911 consecutive patients with non-valvular atrial fibrillation on vitamin-K antagonist. The performance of the re-expressed Modification of Diet in Renal Disease equation vs the new Chronic Kidney Disease Epidemiology Collaboration equation in patients with non-valvular atrial fibrillation with respect to either a composite endpoint of major bleeding, thromboembolic events and all-cause mortality or each individual component of the composite endpoint was assessed using continuous and categorical ≥ 60, 59-30, and < 30 mL/min per 1.73 m² estimated glomerular filtration rate.

RESULTS: During 10 ± 3 mo, the composite endpoint occurred in 98 (10.8%) patients: 30 patients developed major bleeding, 18 had thromboembolic events, and 60 died. The new equation provided lower prevalence of renal dysfunction < 60 mL/min per 1.73 m² (32.9%), compared with the re-expressed equation (34.1%). Estimated glomerular filtration rate from both equations was independent predictor of composite endpoint (HR = 0.98 and 0.97 for the re-expressed and the new equation, respectively; P < 0.0001) and all-cause mortality (HR = 0.98 for both equations, P < 0.01). Strong association with thromboembolic events was observed only when estimated glomerular filtration rate was < 30 mL/min per 1.73 m²: HR is 5.1 for the re-expressed equation, and HR = 5.0 for the new equation. No significant association with major bleeding was observed for both equations.

CONCLUSION: The new equation reduced the prevalence of renal dysfunction. Both equations performed similarly in predicting major adverse outcomes.

Epidemiology of CKD Regression in Patients under Nephrology Care

Chronic Kidney Disease (CKD) regression is considered as an infrequent renal outcome, limited to early stages, and associated with higher mortality. However, prevalence, prognosis and the clinical correlates of CKD regression remain undefined in the setting of nephrology care. This is a multicenter prospective study in 1418 patients with established CKD (eGFR: 60–15 ml/min/1.73m²) under nephrology care in 47 outpatient clinics in Italy from a least one year. We defined CKD regressors as a ΔGFR ≥0 ml/min/1.73 m²/year. ΔGFR was estimated as the absolute difference between eGFR measured at baseline and at follow up visit after 18–24 months, respectively. Outcomes were End Stage Renal Disease (ESRD) and overall-causes Mortality.391 patients (27.6%) were identified as regressors as they showed an eGFR increase between the baseline visit in the renal clinic and the follow up visit. In multivariate regression analyses the regressor status was not associated with CKD stage. Low proteinuria was the main factor associated with CKD regression, accounting per se for 48% of the likelihood of this outcome. Lower systolic blood pressure, higher BMI and absence of autosomal polycystic disease (PKD) were additional predictors of CKD regression. In regressors, ESRD risk was 72% lower (HR: 0.28; 95% CI 0.14–0.57; p<0.0001) while mortality risk did not differ from that in non-regressors (HR: 1.16; 95% CI 0.73–1.83; p = 0.540). Spline models showed that the reduction of ESRD risk associated with positive ΔGFR was attenuated in advanced CKD stage. CKD regression occurs in about one-fourth patients receiving renal care in nephrology units and correlates with low proteinuria, BP and the absence of PKD. This condition portends better renal prognosis, mostly in earlier CKD stages, with no excess risk for mortality.

Population pharmacokinetic approach to evaluate the effect of CYP2D6, CYP3A, ABCB1, POR and NR1I2 genotypes on donepezil clearance

AIMS

A large interindividual variability in plasma concentrations has been reported in patients treated with donepezil, the most frequently prescribed antidementia drug. We aimed to evaluate clinical and genetic factors influencing donepezil disposition in a patient population recruited from a naturalistic setting.

METHODS

A population pharmacokinetic study was performed including data from 129 older patients treated with donepezil. The patients were genotyped for common polymorphisms in the metabolic enzymes CYP2D6 and CYP3A, in the electron transferring protein POR and the nuclear factor NR1I2 involved in CYP activity and expression, and in the drug transporter ABCB1.

RESULTS

The average donepezil clearance was 7.3 l h(-1) with a 30% interindividual variability. Gender markedly influenced donepezil clearance (P < 0.01). Functional alleles of CYP2D6 were identified as unique significant genetic covariate for donepezil clearance (P < 0.01), with poor metabolizers and ultrarapid metabolizers demonstrating, respectively, a 32% slower and a 67% faster donepezil elimination compared with extensive metabolizers.

CONCLUSION

The pharmacokinetic parameters of donepezil were well described by the developed population model. Functional alleles of CYP2D6 significantly contributed to the variability in donepezil disposition in the patient population and should be further investigated in the context of individual dose optimization to improve clinical outcome and tolerability of the treatment.

Choice of Estimated Glomerular Filtration Rate Equation Impacts Drug-Dosing Recommendations and Risk Stratification in Patients With Chronic Kidney Disease Undergoing Percutaneous Coronary Interventions

BACKGROUND

Multiple equations exist to estimate glomerular filtration rate (GFR); however, there is no consensus on which is superior for risk classification in patients with chronic kidney disease (CKD) undergoing percutaneous coronary intervention (PCI).

OBJECTIVES

The goals of this study were to identify which equation to estimate GFR is superior for predicting adverse outcomes after PCI and to examine how equation selection would impact drug-dosing recommendations.

METHODS

Estimated GFR (eGFR) was calculated with the Cockcroft-Gault, Modification of Diet in Renal Disease Study (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations for 128,805 patients undergoing PCI in the state of Michigan. Agreement between patient pre-PCI eGFR estimates and resultant CKD stage classifications, their ability to discriminate post-procedural in-hospital clinical outcomes, and the impact of equation choice on dosing recommendations for commonly used antiplatelet and antithrombotic medications were investigated.

RESULTS

CKD-EPI best discriminated post-PCI mortality by receiver operator characteristic analysis. There was wide variability in eGFR, which persisted after grouping by CKD stages. Reclassification by CKD-EPI resulted in net reclassification index improvement for acute kidney injury and new requirement for dialysis. Equation choice affected drug-dosing recommendations, with the formulas agreeing for only 50.3%, 40.0%, and 34.3% of potentially impacted patients for eGFR cutoffs of <60, <50, and <30 ml/min/1.73 m(2), respectively.

CONCLUSIONS

Different eGFR equations result in CKD stage reclassification that has major clinical implications for predicting adverse outcomes after PCI and drug-dosing recommendations. Our results support the use of CKD-EPI for risk stratification among patients undergoing PCI.

Early chronic kidney disease: diagnosis, management and models of care

Chronic kidney disease (CKD) is prevalent in many countries, and the costs associated with the care of patients with end-stage renal disease (ESRD) are estimated to exceed US$1 trillion globally. The clinical and economic rationale for the design of timely and appropriate health system responses to limit the progression of CKD to ESRD is clear. Clinical care might improve if early-stage CKD with risk of progression to ESRD is differentiated from early-stage CKD that is unlikely to advance. The diagnostic tests that are currently used for CKD exhibit key limitations; therefore, additional research is required to increase awareness of the risk factors for CKD progression. Systems modelling can be used to evaluate the impact of different care models on CKD outcomes and costs. The US Indian Health Service has demonstrated that an integrated, system-wide approach can produce notable benefits on cardiovascular and renal health outcomes. Economic and clinical improvements might, therefore, be possible if CKD is reconceptualized as a part of primary care. This Review discusses which early CKD interventions are appropriate, the optimum time to provide clinical care, and the most suitable model of care to adopt.

LC-MS/MS Method for Serum Creatinine: Comparison with Enzymatic Method and Jaffe Method

Accurate quantification of creatinine (Cre) is important to estimate glomerular filtration rate (GFR). Differences among various methods of Cre quantification were previously noted. This study aims to develop a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for serum Cre and compare this method with clinical routine methods. LC-MS/MS analysis was performed on API 4000 triple quadrupole mass spectrometer coupled with an Agilent 1200 liquid chromatography system. After adding isotope-labeled Cre-d3 as internal standard, serum samples were prepared via a one-step protein precipitation with methanol. The LC-MS/MS method was compared with frequently used enzymatic method and Jaffe method. This developed method, with a total run time of 3 min, had a lower limit of quantification of 4.4 μmol/L, a total imprecision of 1.15%–3.84%, and an average bias of 1.06%. No significant matrix effect, carryover, and interference were observed for the LC-MS/MS method. The reference intervals of serum Cre measured by LC-MS/MS assay were 41–79 μmol/L for adult women, and 46–101 μmol/L for adult men. Using LC-MS/MS as a reference, the enzymatic method showed an average bias of -2.1% and the Jaffe method showed a substantial average bias of 11.7%. Compared with the LC-MS/MS method, significant negative bias was observed for the enzymatic and Jaffe methods in hemolytic and lipimic samples. We developed a simple, specific, and accurate LC-MS/MS method to analyze serum Cre. Discordance existed among different methods.

Estimated glomerular filtration rates cannot replace measured GFR in type 1 diabetes patients with hyperfiltration

AIM

This study of children and young adults with type 1 diabetes with normal to high glomerular filtration rates (GFR) compared estimated GFR (eGFR) with measured GFR (mGFR).

METHODS

GFR was measured by inulin clearance, and we carried out simultaneous analyses of standardised creatinine and cystatin C. eGFR was calculated using different formulas.

RESULTS

We enrolled 106 patients, including 56 males, aged 21.9 (standard deviation 9.2) years with 13.7 (9.1) years' duration of diabetes and a mean haemoglobin A1c (HbA1c ) of 7.7% (61 mmol/mol). The median mGFR was 128 (111-143) mL/min/1.73 m(2) . Most of the eGFR estimations failed to detect a significant proportion of hyperfiltration based on inulin clearance. The best accuracy (P30) between eGFR and mGFR was seen with eGFRCKD - EPI (92%), eGFRcys C Berg (86%), eGFRcys C CAPA (78%) and eGFRcys C Inker (84%) where eGFRCKD - EPI and eGFR cys C Berg showed the lowest bias. Most eGFRcys C measurements showed greater accuracy when combined with eGFRcr (P30 92-94%).

CONCLUSION

The best accuracy (P30) and lowest bias were found with eGFRCKD - EPI and eGFR Berg. in this cohort. However, eGFR cannot accurately replace mGFR to detect hyperfiltration and follow GFR over time in young patients with type 1 diabetes.

Recalibration of blood analytes over 25 years in the atherosclerosis risk in communities study: impact of recalibration on chronic kidney disease prevalence and incidence

BACKGROUND

Equivalence of laboratory tests over time is important for longitudinal studies. Even a small systematic difference (bias) can result in substantial misclassification.

METHODS

We selected 200 Atherosclerosis Risk in Communities Study participants attending all 5 study visits over 25 years. Eight analytes were remeasured in 2011-2013 from stored blood samples from multiple visits: creatinine, uric acid, glucose, total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, and high-sensitivity C-reactive protein. Original values were recalibrated to remeasured values with Deming regression. Differences >10% were considered to reflect substantial bias, and correction equations were applied to affected analytes in the total study population. We examined trends in chronic kidney disease (CKD) pre- and postrecalibration.

RESULTS

Repeat measures were highly correlated with original values [Pearson r > 0.85 after removing outliers (median 4.5% of paired measurements)], but 2 of 8 analytes (creatinine and uric acid) had differences >10%. Original values of creatinine and uric acid were recalibrated to current values with correction equations. CKD prevalence differed substantially after recalibration of creatinine (visits 1, 2, 4, and 5 prerecalibration: 21.7%, 36.1%, 3.5%, and 29.4%, respectively; postrecalibration: 1.3%, 2.2%, 6.4%, and 29.4%). For HDL cholesterol, the current direct enzymatic method differed substantially from magnesium dextran precipitation used during visits 1-4.

CONCLUSIONS

Analytes remeasured in samples stored for approximately 25 years were highly correlated with original values, but 2 of the 8 analytes showed substantial bias at multiple visits. Laboratory recalibration improved reproducibility of test results across visits and resulted in substantial differences in CKD prevalence. We demonstrate the importance of consistent recalibration of laboratory assays in a cohort study.

Renal dosing in high-risk populations

In patients with diminished kidney function, the pharmacokinetics of many medications are altered. Alterations in absorption, distribution, and metabolism are observed in addition to altered elimination through the kidney. Classes of intravenous medications in which dose modifications are frequently required for patients with diminished kidney function include antibiotics, some anticoagulants, and chemotherapy agents. Failure to follow renal dose adjustment recommendations can lead to an increased risk of toxicity. Equations frequently used to estimate kidney function for the purpose of making renal dose adjustments include the Cockcroft-Gault, Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.

Risk of ESRD and death in patients with CKD not referred to a nephrologist: a 7-year prospective study

BACKGROUND AND OBJECTIVES

Rising prevalence of CKD requires active involvement of general practitioners to limit ESRD and mortality risk. However, the outcomes of patients with CKD exclusively managed by general practitioners are ill defined.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We prospectively evaluated 30,326 adult patients with nondialysis CKD stages 1-5 who had never received consultation in tertiary nephrology care recruited from 700 general practitioner offices in Italy during 2002 and 2003. CKD stages were classified as stages 1 and 2 (GFR ≥ 60 ml/min per 1.73 m(2) and either albuminuria or an International Classification of Diseases, Ninth Revision, Clinical Modification code for kidney disease), stage 3a (GFR=59-45), stage 3b (GFR=44-30), stage 4 (GFR=29-15), and stage 5 (GFR<15). Primary outcome was the risk of ESRD (dialysis or transplantation) or all-cause death.

RESULTS

Overall 64% of patients were in stage 3a, and 4.5% of patients were in stages 3b-5. Patients with stages 1 and 2 were younger, were predominantly men, more frequently had diabetes, and had lower prevalence of previous cardiovascular disease than patients with stages 3a-5. Hypertension was frequent in all CKD stages (80%-94%), whereas there was a lower prevalence of dyslipidemia, albuminuria, and obesity associated with more advanced CKD. During the follow-up (median=7.2 years; interquartile range=4.7-7.7), 6592 patients died and 295 started ESRD. Compared with stages 1 and 2 (reference), mortality risk (hazard ratio, 95% confidence interval) was higher in stages 3b-5 (1.66, 1.49-1.86, 2.75, 2.41-3.13 and 2.54, 2.01-3.22, respectively) but not stage 3a (1.11, 0.99-1.23). Similarly, ESRD risk (hazard ratio, 95% confidence interval) was not higher at stage 3a (1.44, 0.79-2.64) but was greater in stages 3b-5 (11.0, 6.3-19.5, 91.2, 53.2-156.2 and, 122.8, 67.9-222.0, respectively). Among modifiable risk factors, anemia and albuminuria significantly predicted either outcome, whereas hypertension only predicted mortality.

CONCLUSIONS

In patients with CKD not referred to nephrology, risks of ESRD and mortality were higher in those with CKD stages 3b-5.

Relative performance of three formulas to assess renal function at predicting in-hospital hemorrhagic complications in an acute coronary syndrome population. What does the new CKD-EPI formula provide?

AIMS

Assessment of renal function is important for bleeding risk stratification in acute coronary syndrome (ACS). There are three formulas routinely used to assess renal function: the Cockroft-Gault (C-G) formula, the MDRD-4 formula and the new Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Our aim was to compare the ability of these formulas to predict the risk of in-hospital bleeding in patients with ACS.

METHODS

The study included 3270 patients with ACS. The performance of each formula with respect to in-hospital TIMI (Thrombolysis In Myocardial Infarction) major or TIMI minor bleeding were assessed using continuous data and by dividing patients into four subgroups according to the estimated glomerular filtration rate (eGFR): ≥90, 89-60, 30-59 and <30 ml/min/1.73 m(2).

RESULTS

Bleeding predictive ability was significantly higher for the C-G formula than for MDRD-4 and CKD-EPI formulas, as evaluated by the area under the curve (AUC); continuous eGFR AUCs: 0.73, 0.69 and 0.71, respectively; categorical eGFR AUCs: 0.71, 0.66 and 0.68, respectively. Net reclassification improvement based on the eGFR categories was significantly positively favored C-G: 9.5% (95% confidence interval (CI) 1.8-17.2%) and 19.1% (95% CI 11.3-26.9%) compared with CKD-EPI and MDRD-4, respectively. After multivariable adjustment, the C-G formula predicted in-hospital bleeding better than MDRD-4 formula (severe renal dysfunction vs. normal renal function: odds ratio 7.98, 95% CI 2.61-24.38 with C-G; odds ratio 3.76, 95% CI 1.63-8.69 with MDRD-4; and odds ratio 5.77, 95% CI 2.18-15.24 with CKD-EPI.

CONCLUSIONS

Our findings suggest that the C-G eGFR may improve risk prediction of in-hospital bleeding more than the MDRD-4 equation and the new CKD-EPI equation in patients with ACS.

Calibration and precision of serum creatinine and plasma cystatin C measurement: impact on the estimation of glomerular filtration rate

Serum creatinine (SCr) is the main variable for estimating glomerular filtration rate (GFR). Due to inter-assay differences, the prevalence of chronic kidney disease (CKD) varies according to the assay used, and calibration standardization is necessary. For SCr, isotope dilution mass spectrometry (IDMS) is the gold standard. Systematic differences are observed between Jaffe and enzymatic methods. Manufacturers subtract 0.30 mg/dl from Jaffe results to match enzymatic results ('compensated Jaffe method'). The analytical performance of enzymatic methods is superior to that of Jaffe methods. In the original Modification of Diet in Renal Disease (MDRD) equation, SCr was measured by a Jaffe Beckman assay, which was later recalibrated. A limitation of this equation was an underestimation of GFR in the high range. The Chronic Kidney Disease Epidemiology (CKD-EPI) consortium proposed an equation using calibrated and IDMS traceable SCr. The gain in performance was due to improving the bias whereas the precision was comparable. The CKD-EPI equation performs better at high GFR levels (GFR >60 ml/min/1.73 m(2)). Analytical limitations have led to the recommendation to give a grade (>60 ml/min/1.73 m(2)) rather than an absolute value with the MDRD equation. By using both enzymatic and calibrated methods, this cutoff-grade could be increased to 90 ml/min/1.73 m(2) (with MDRD) and 120 ml/min/1.73 m(2) (with CKD-EPI). The superiority of the CKD-EPI equation over MDRD is analytical, but the precision gain is limited. IDMS traceable enzymatic methods have been used in the development of the Lund-Malmö (in CKD populations) and Berlin Initiative Study equations (in the elderly). The analytical errors for cystatin C are grossly comparable to issues found with SCr. Standardization is available since 2011. A reference method for cystatin C is still lacking. Equations based on standardized cystatin C or cystatin C and creatinine have been proposed. The better performance of these equations (especially the combined CKD-EPI equation) has been demonstrated.

Comparison of chronic kidney disease prevalence examined by the chronic kidney disease epidemiology collaboration equation with that by the modification of diet in renal disease equation in Korean adult population

BACKGROUND

The new estimated glomerular filtration (eGFR) equation, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, was recently introduced. We compared the prevalence of CKD examined by the CKD-EPI equation with that by the Modification of Diet in Renal Disease (MDRD) equation.

METHODS

We analyzed the data from a total of 14,605 Korean adults (age ≥20 years), who were enrolled in the Korean National Health and Nutrition Examination Survey in 2007, 2009, and 2010. CKD stages 1 and 2 were defined as eGFR ≥60 mL/min/1.73 m(2) with proteinuria measured by dipstick. CKD stages 3-5 were defined as eGFR <60 mL/min/1.73 m(2) .

RESULTS

The eGFRs calculated by the CKD-EPI equation were higher than those calculated by the MDRD equation (P < 0.001), especially in women and young people. The prevalence of CKD stages 3-5 calculated by the MDRD equation was 6.8%, 3.0%, and 3.0% in 2007, 2009, and 2010, respectively. The prevalence of CKD stages 3-5 calculated by CKD-EPI equation was 7.7%, 2.7%, and 2.6% in 2007, 2009, and 2010, respectively. When defining the CKD using the CKD-EPI equation, 55 (32.7%) of 350 cases were reclassified into more advanced stages and 295 cases (67.3%) were reclassified into less-advanced stages.

CONCLUSION

The CKD-EPI equation caused an overall low prevalence of CKD compared to the MDRD. Therefore, CKD-EPI equation might be helpful to prevent an overestimation of CKD.

The glomerular filtration rate estimated by new and old equations as a predictor of important outcomes in elderly patients

BACKGROUND

The prevalence of chronic kidney disease (CKD) increases with age, and new glomerular filtration rate-estimating equations have recently been validated. The epidemiology of CKD in older individuals and the relationship between a low estimated glomerular filtration rate as calculated by these equations and adverse outcomes remains unknown.

METHODS

Data from the BELFRAIL study, a prospective, population-based cohort study of 539 individuals aged 80 years and older, were used. For every participant, five equations were used to calculate estimated glomerular filtration rate based on serum creatinine and/or cystatin C values: MDRD, CKD-EPIcreat, CKD-EPIcyst, CKD-EPIcreatcyst, and BIS equations. The outcomes analyzed included mortality combined with the necessity of new renal replacement therapy, severe cardiovascular events, and hospitalization.

RESULTS

During the follow-up period, which was an average of 2.9 years, 124 participants died, 7 required renal replacement therapy, 271 were hospitalized, and 73 had a severe cardiovascular event. The prevalence of estimated glomerular filtration rate values <60 mL/min/1.73 m2 differed depending on the equation used as follows: 44% (MDRD), 45% (CKD-EPIcreat), 75% (CKD-EPIcyst), 65% (CKD-EPIcreatcyst), and 80% (BIS). All of the glomerular filtration rate-estimating equations revealed that higher cardiovascular mortality was associated with lower estimated glomerular filtration rates and that higher probabilities of hospitalization were associated with estimated glomerular filtration rates <30 mL/min/1.73 m2. A lower estimated glomerular filtration rate did not predict a higher probability of severe cardiovascular events, except when using the CKD-EPIcyst equation. By calculating the net reclassification improvement, CKD-EPIcyst and CKD-EPIcreatcyst were shown to predict mortality (+25% and +18%) and severe cardiovascular events (+7% and +9%) with the highest accuracy. The BIS equation was less accurate in predicting mortality (-12%).

CONCLUSION

Higher prevalence of CKD were found using the CKD-EPIcyst, CKD-EPIcreatcyst, and BIS equations compared with the MDRD and CKD-EPIcreat equations. The new CKD-EPIcreatcyst and CKD-EPIcyst equations appear to be better predictors of mortality and severe cardiovascular events.

MDRD versus CKD-EPI equation to estimate glomerular filtration rate in kidney transplant recipients

BACKGROUND

The new Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine-based equation was developed to address the systematic underestimation of the glomerular filtration rate (GFR) by the Modification of Diet in Renal Disease (MDRD) Study equation in patients with a relatively well-preserved kidney function. The performance of the new equation for kidney transplant recipients is discussed.

METHODS

We analyzed the performances of the CKD-EPI equation in comparison with the MDRD Study equation in 825 stable kidney transplant recipients. Bias, precision, and accuracy within 30% of true GFR were determined. GFR was measured by urinary clearance of inulin (n=488) and plasma clearance of Cr-EDTA (n=337).

RESULTS

Mean measured GFR (mGFR) was 50±19 mL/min/1.73 m. On the whole cohort, bias was significantly lower for MDRD Study equation compared with CKD-EPI creatinine. This superiority translates into a better accuracy (80% and 74% for the MDRD and CKD-EPI creatinine, respectively). The best performance of the MDRD Study equation is confirmed both in the subgroups of patients with mGFR <60 mL/min/1.73 m and between 60 and 90 mL/min/1.73 m. For mGFR >90 mL/min/1.73 m, there were no significant differences between the two equations in terms of performance.

CONCLUSIONS

The CKD-EPI creatinine equation does not offer a better GFR prediction in renal transplant patients compared with the MDRD Study equation, even in the earlier CKD stages.

Normoalbuminuric diabetic kidney disease in the U.S. population

BACKGROUND

This study sought to compare the prevalence and modifying factors of normoalbuminuric (NA) versus albuminuric (ALB) CKD in the U.S. diabetic and nondiabetic populations.

METHODS

NHANES 2001-2008 included 2798 diabetic and 15,743 nondiabetic participants. Age-specific prevalence of NA-CKD and ALB-CKD was calculated within each diabetes stratum and then stratified again according to gender, ethnicity, mean arterial pressure ≥105 mmHg and HbA1c≥7%. Multivariate regression analyses were performed to determine odds ratios and 95% CI for NA-CKD.

RESULTS

Prevalence of NA-CKD rose with age, with an overall mean of 9.7% in diabetic and 4.3% in nondiabetic participants. NA-CKD was less prevalent in diabetic men, OR=0.58 (95% CI: 0.39, 0.87). In comparison with whites, blacks and 'other' ethnic groups had an OR for NA-CKD of 0.44 (95% CI 0.29, 0.68) and 0.57 (95% CI: 0.34, 0.96), respectively. Poorly controlled blood pressure and glycemia resulted in a decreased OR for NA-CKD (OR = 0.25, 95% CI: 0.13, 0.50) and (0.48, 95% CI: 0.31, 0.74), respectively. Similar results were obtained for nondiabetic participants.

CONCLUSIONS

NA-CKD is more common in people with diabetes, women, non-Hispanic whites, and in the setting of well controlled blood pressure and glycemia.

Biochemical markers of aging for longitudinal studies in humans

Much progress has been made in the past decades in unraveling the mechanisms that are responsible for aging. The discovery that particular gene mutations in experimental species such as yeast, flies, and nematodes are associated with longevity has led to many important insights into pathways that regulate aging processes. However, extrapolating laboratory findings in experimental species to knowledge that is valid for the complexity of human physiology remains a major challenge. Apart from the restricted experimental possibilities, studying aging in humans is further complicated by the development of various age-related diseases. The availability of a set of biomarkers that really reflect underlying aging processes would be of much value in disentangling age-associated pathology from specific aging mechanisms. In this review, we survey the literature to identify promising biochemical markers of aging, with a particular focus on using them in longitudinal studies of aging in humans that entail repeated measurements on easily obtainable material, such as blood samples. Our search strategy was a 2-pronged approach, one focused on general mechanisms of aging and one including studies on clinical biomarkers of age-related diseases.

GFR estimation using standardized cystatin C in kidney transplant recipients

BACKGROUND

The utility of serum cystatin C (SCysC) as a filtration marker in kidney transplantation is uncertain. We took advantage of the recent validation of a reference calibrator for SCysC and of newly developed CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equations (2012) expressed for use with standardized SCysC level to reassess the performance of SCysC as a filtration marker in kidney transplant recipients.

STUDY DESIGN

Study of diagnostic test accuracy.

SETTING & PARTICIPANTS

670 kidney transplant recipients from 3 centers undergoing glomerular filtration rate (GFR) measurements from December 2006 to November 2012.

INDEX TEST

Estimated GFR (eGFR) using the 2012 SCysC-based and serum creatinine (SCr)/SCysC-based CKD-EPI equations (eGFR(cys) and eGFR(cr-cys), respectively) and the 2009 SCr-based CKD-EPI equation (eGFR(cr)), with SCysC and SCr measured at a single laboratory between April 2011 and June 2011.

REFERENCE TEST

Measured GFR (mGFR) using urinary clearance of inulin.

RESULTS

Bias (the difference between mGFR and eGFR) was significantly smaller for eGFR(cys) and eGFR(cr-cys) versus eGFR(cr) (-2.82 and -0.54 vs +4.4 mL/min/1.73 m(2), respectively; P < 0.001). Precision (standard deviation of the mean bias) also was better for eGFR(cys) and eGFR(cr-cys) versus eGFR(cr) (12 and 11 vs 13 mL/min/1.73 m(2) [P < 0.001 for both comparisons]). Accuracy (percentage of GFR estimates within 30% of mGFR) was greater for eGFR(cys) and eGFR(cr-cys) versus eGFR(cr) (81% and 86% vs 75%, respectively [P = 0.004 and P < 0.001]). Net reclassification index with respect to mGFR of 30 mL/min/1.73 m(2) for eGFR(cr-cys) and eGFR(cys) versus eGFR(cr) was 18.8% [95% CI, 8.6%-28.9%] and 22.5% [95% CI, 10.2%-34.9%].

LIMITATIONS

Patients were exclusively of European descent; association with transplant outcome was not evaluated.

CONCLUSIONS

Our data validate the use of both the newly developed SCysC-based and SCr/SCysC-based CKD-EPI equations (2012) in kidney transplant recipients. Both equations perform better than the SCr-based CKD-EPI equation (2009).

Clinical evaluation of analytical variations in serum creatinine measurements: why laboratories should abandon Jaffe techniques

BACKGROUND

Non-equivalence in serum creatinine (SCr) measurements across Dutch laboratories and the consequences hereof on chronic kidney disease (CKD) staging were examined.

METHODS

National data from the Dutch annual external quality organization of 2009 were used. 144 participating laboratories examined 11 pairs of commutable, value-assigned SCr specimens in the range 52-262 μmol/L, using Jaffe or enzymatic techniques. Regression equations were created for each participating laboratory (by regressing values as measured by participating laboratories on the target values of the samples sent by the external quality organization); area under the curves were examined and used to rank laboratories. The 10th and 90th percentile regression equation were selected for each technique separately. To evaluate the impact of the variability in SCr measurements and its eventual clinical consequences in a real patient population, we used a cohort of 82424 patients aged 19-106 years. The SCr measurements of these 82424 patients were introduced in the 10th and 90th percentile regression equations. The newly calculated SCr values were used to calculate an estimated glomerular filtration rate (eGFR) using the 4-variable Isotope Dilution Mass Spectrometry traceable Modification of Diet in Renal Disease formula. Differences in CKD staging were examined, comparing the stratification outcomes for Jaffe and enzymatic SCr techniques.

RESULTS

Jaffe techniques overestimated SCr: 21%, 12%, 10% for SCr target values 52, 73 and 94 μmol/L, respectively. For enzymatic assay these values were 0%, -1%, -2%, respectively. eGFR using the MDRD formula and SCr measured by Jaffe techniques, staged patients in a lower CKD category. Downgrading to a lower CKD stage occurred in 1-42%, 2-37% and 12-78.9% of patients for the 10th and 90th percentile laboratories respectively in CKD categories 45-60, 60-90 and >90 ml/min/1.73 m2. Using enzymatic techniques, downgrading occurred only in 2-4% of patients.

CONCLUSIONS

Enzymatic techniques lead to less variability in SCr measurements than Jaffe techniques, and therefore result in more accurate staging of CKD. Therefore the specific enzymatic techniques are preferably used in clinical practice in order to generate more reliable GFR estimates.

Accuracy of a GFR estimating equation over time in people with a wide range of kidney function

BACKGROUND

Change in glomerular filtration rate (GFR) is important for clinical decision making. GFR estimates from serum creatinine level provide an unbiased but imprecise estimate of GFR at single time points. However, the accuracy of estimated GFR over time is not well known.

STUDY DESIGN

Longitudinal study of diagnostic test accuracy.

SETTINGS & PARTICIPANTS

4 clinical trials with longitudinal measurements of GFR and serum creatinine on the same day, including individuals with and without kidney disease with a wide range of kidney function, diverse racial backgrounds, and varied clinical characteristics.

INDEX TEST

GFR estimated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.

REFERENCE TEST

GFR measured using urinary clearance of (125)I-iothalamate.

RESULTS

Data included 19,735 GFR measurements in 3,531 participants during a mean follow-up of 2.6 years. Mean values at baseline for measured and estimated GFR and error (measured GFR - estimated GFR) were 73.1 (95% CI, 71.6 to 74.5), 72.7 (95% CI, 71.5 to 74.0), and 0.14 (95% CI, -0.35 to 0.63) mL/min/1.73 m(2), respectively. Mean rates of change in measured and estimated GFR and error were -2.3 (95% CI, -2.4 to -2.1), -2.2 (95% CI, -2.4 to -2.1), and -0.09 (95% CI, -0.24 to 0.05) mL/min/1.73 m(2) per year (P < 0.001, P < 0.001, and P = 0.2, respectively). Variability (ie, standard deviation) among participants in rate of change in measured GFR, estimated GFR, and error was 4.3, 3.4, and 3.3 mL/min/1.73 m(2) per year, respectively. Only 15% of participants had a rate of change in error >3 mL/min/1.73 m(2) per year, and only 2% had a rate of change in error >5% per year.

LIMITATIONS

Participants' characteristics were not available over time.

CONCLUSION

The accuracy of GFR estimates did not change over time. Clinicians should interpret changes in estimated GFR over time as reflecting changes in measured GFR rather than changes in errors in the GFR estimates in most individuals.

[Pharmacotherapy in patients suffering from chronic kidney disease]

The number of patients suffering from chronic kidney disease (CKD) is increasing worldwide and exceeds 15% of the entire population in industrialized countries. Half of the patients aged 70 + years suffer from CKD. The most prevalent underlying diseases leading to CKD are diabetes and hypertension. CKD per se increases the risk of cardiovascular events, cancer, and infections; hence, adequate and intensified pharmacotherapy is of utmost importance in this patient population. About 60% of all regularly used drugs are excreted by the kidney. For those, dose adjustment is of utter importance to avoid untoward effects and serious complications. The first important step for dose adjustment is the accurate estimation of renal function, i.e., glomerular filtration rate (GFR). Renal function cannot be assessed by serum creatinine alone as it only rises after a substantial (> 50%) loss of glomerular function and depends on many factors, e.g., age, gender, weight, and race. GFR can easily be estimated using formulas, e.g., the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula.

External validation of aminoglycoside models used in web calculators and clinical decision support systems after laboratory conversion to serum creatinine isotope dilution mass spectrometry assay

BACKGROUND

Models to predict gentamicin t(½) from serum creatinine (SCr) estimated creatinine clearance (CrCl) are currently being incorporated into smart-device applications and clinical decision support modules without external validation.

OBJECTIVE

The aim of this study was to determine whether such models remain viable after conversion to isotope dilution mass spectrometry (IDMS) SCr assay.

METHODS

This study analyzed data from retrospective reviews of the medical records of nonobese adults receiving the aminoglycoside gentamicin and having ≥2 evaluable serum gentamicin concentrations after laboratory IDMS SCr conversion, from January 2008 to August 2009, at a tertiary care hospital in Florida. A literature search found a number of cited aminoglycoside models. This group of models was classified as group 1. The World Wide Web was also searched for the term aminoglycoside dosing calculators, with 6 models found and referred to as group 2. Predictive performance measures were used to compare the model results with the t(½) calculated from gentamicin concentrations using the Nelder-Mead algorithm.

RESULTS

The records of 39 patients met the inclusion criteria (23 men, 16 women; age range, 18-86 years; range of estimated CrCl, 55-115 mL/min) and provided the "gold standard" aminoglycoside t(½). A gentamicin t(½) was predicted from several published models (group 1) and from other models used in online smart-device applications (group 2) and clinical decision modules. The median (interquartile range) root mean square errors were 0.48 (0.44 to 0.65) and 0.48 (0.45 to 0.70) hours from group-1 and -2 models, respectively. The median mean relative prediction errors were 9% (-14% to +13%) and 11% (+1% to +21%) from groups 1 and 2. The median mean absolute prediction errors were 21% (19% to 28%) and 21% (20% to 30%) from groups 1 and 2. Adjusting SCr by +20% improved the predictive ability in 3 of 12 cited models and in 5 of 6 models used in applications.

CONCLUSIONS

Models to predict gentamicin t(½) should be externally validated at one's institution before use. The findings from the present study provide a framework for conducting external validation.

Glomerular filtration rate estimation in patients with type 2 diabetes: creatinine- or cystatin C-based equations?

AIMS/HYPOTHESIS

It is argued that GFR estimation (eGFR) using cystatin C-based equations (eGFRcys) is superior to that using creatinine-based equations (eGFRcre). We investigated whether eGFRcys are superior to eGFRcre in patients with type 2 diabetes.

METHODS

GFR was measured in 448 type 2 diabetic patients using (51)Cr-EDTA-measured GFR (mGFR) as the reference standard. Bias, precision and accuracy of eGFRcys and eGFRcre were compared.

RESULTS

The most accurate eGFRcre equation (Chronic Kidney Disease Epidemiology Collaboration [CKD-EPI]), which produced the highest proportion of estimates that were within 30% and 10% of the reference standard (80.7% and 38.0% of samples, respectively) had a bias of 7.1 and precision of 12.0 ml min(-1) 1.73 m(-2). The calibrated eGFRcys with the highest accuracy (Tan-C), which produced the highest proportion of estimates that were within 30% (78.8%) and within 10% (39.0%) of the reference standard had a bias of -3.5 and precision of 18.0 ml min(-1) 1.73 m(-2). Moreover, the areas under the receiver operating curve were higher with eGFRcre (CKD-EPI and Modification of Diet in Renal Disease [MDRD]) than with eGFRcys for the diagnosis of mild (mGFR <90 ml min(-1) 1.73 m(-2)) and moderate (mGFR <60 ml min(-1) 1.73 m(-2)) chronic kidney disease. In patients with mGFR ≥90 ml min(-1) 1.73 m(-2), CKD-EPI was the least biased, the most precise and the most accurate equation.

CONCLUSIONS/INTERPRETATION

In patients with type 2 diabetes, eGFRcys do not currently provide better eGFR than eGFRcre. At present, compared with eGFRcys, eGFRcre are better at predicting the stage of chronic kidney disease. In addition, CKD-EPI seems to be the best equation for eGFR in patients with normal renal function.

Glomerular filtration rate estimation in patients with type 2 diabetes: creatinine- or cystatin C-based equations?

AIMS/HYPOTHESIS

It is argued that GFR estimation (eGFR) using cystatin C-based equations (eGFRcys) is superior to that using creatinine-based equations (eGFRcre). We investigated whether eGFRcys are superior to eGFRcre in patients with type 2 diabetes.

METHODS

GFR was measured in 448 type 2 diabetic patients using (51)Cr-EDTA-measured GFR (mGFR) as the reference standard. Bias, precision and accuracy of eGFRcys and eGFRcre were compared.

RESULTS

The most accurate eGFRcre equation (Chronic Kidney Disease Epidemiology Collaboration [CKD-EPI]), which produced the highest proportion of estimates that were within 30% and 10% of the reference standard (80.7% and 38.0% of samples, respectively) had a bias of 7.1 and precision of 12.0 ml min(-1) 1.73 m(-2). The calibrated eGFRcys with the highest accuracy (Tan-C), which produced the highest proportion of estimates that were within 30% (78.8%) and within 10% (39.0%) of the reference standard had a bias of -3.5 and precision of 18.0 ml min(-1) 1.73 m(-2). Moreover, the areas under the receiver operating curve were higher with eGFRcre (CKD-EPI and Modification of Diet in Renal Disease [MDRD]) than with eGFRcys for the diagnosis of mild (mGFR <90 ml min(-1) 1.73 m(-2)) and moderate (mGFR <60 ml min(-1) 1.73 m(-2)) chronic kidney disease. In patients with mGFR ≥90 ml min(-1) 1.73 m(-2), CKD-EPI was the least biased, the most precise and the most accurate equation.

CONCLUSIONS/INTERPRETATION

In patients with type 2 diabetes, eGFRcys do not currently provide better eGFR than eGFRcre. At present, compared with eGFRcys, eGFRcre are better at predicting the stage of chronic kidney disease. In addition, CKD-EPI seems to be the best equation for eGFR in patients with normal renal function.

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.

The impact of interlaboratory differences in cystatin C assay measurement on glomerular filtration rate estimation

BACKGROUND AND OBJECTIVES

Cystatin C (CysC) is a promising marker of GFR. Several equations have been derived to estimate GFR from its serum concentration. Heterogeneity in the performance of these equations exists in validation studies even when the same CysC assay from the same manufacturer is utilized. This study was designed to examine the differences in CysC and GFR estimation (eGFR) using Siemens' nephelometric immunoassay and the Mayo Clinic equation. The ability of the eGFRs to predict measured GFR was also examined.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Ninety-seven split samples were sent to laboratories at Children's Hospital of Eastern Ontario (CHEO) in Ottawa, Canada, and at the Mayo Clinic in Rochester, Minnesota.

RESULTS

The mean CHEO CysC was 0.17 mg/L (10%) lower than the mean Mayo Clinic CysC. Using the Mayo Clinic equation, the mean eGFR difference was 7.2 ml/min per 1.73 m(2) (15%). Approximately 36% of the results agreed within 10%, while 13% were discordant by greater than 30%. Larger absolute differences in mean eGFR between the two laboratories were found in the subgroup with CysC less than 1.41 mg/L as compared with the subgroup greater than 1.41 mg/L (9.5 versus 5.0 ml/min per 1.73 m(2)). Correction of CHEO values to the Mayo Clinic did not improve GFR estimation.

CONCLUSIONS

Significant differences in CysC measurement exist between laboratories using the same assay by the same manufacturer and these lead to clinically relevant differences in GFR estimation. This interlaboratory variability needs to be recognized when interpreting and comparing CysC and eGFR results.

A multicentric evaluation of IDMS-traceable creatinine enzymatic assays

Chronic kidney disease definition is based on glomerular filtration rate (GFR) estimations which are derived from creatinine-based equations. The accuracy of GFR estimation is thus largely dependent of those of serum creatinine assays. International recommendations highlight the need for traceable creatinine assays. The French Society of Clinical Biochemistry conducted a study for measuring accuracy of creatinine enzymatic methods. This evaluation involved 25 clinical laboratories. Creatinine was measured in serum pools ranging from 35.9±0.9 μmol/L to 174.5±3.1 μmol/L (IDMS determination) using 12 creatinine enzymatic methods. For all creatinine values greater than 74.4±1.4 μmol/L, the bias and imprecision did not exceed 5% and 5.9%, respectively. For the lowest value (35.9±0.9 μmol/L), the bias ranged from -1.8 to 9.9% (with one exception). At this level, the imprecision ranged from 1.9 to 7.8%. The true performances of the assays (couples of bias and relative standard deviation), were evaluated using Monte-Carlo simulations. Most of the assays fall within the maximum Total Error of 12% at all concentrations. This study demonstrates substantial improvements in the calibration, traceability and precision of the enzymatic methods, reaching the NKDEP recommendations. Moreover, most of these assays allowed accurate creatinine measurements for creatinine levels lower than 40 μmol/L.