A simplified Cockcroft-Gault formula to improve the prediction of the glomerular filtration rate in diabetic patients

Chronic kidney disease staging with cystatin C or creatinine-based formulas: flipping the coin

Background

Chronic kidney disease (CKD) affects 10-13% of the population worldwide. CKD classification stratifies patients in five stages of risk for progressive renal disease based on estimated glomerular filtration rate (eGFR) by formulas and albuminuria. However, the reliability of formulas to reflect real renal function is a matter of debate. The effect of the error of formulas in the CKD classification is unclear, particularly for cystatin C-based equations.

Methods

We evaluated the reliability of a large number of cystatin C and/or creatinine-based formulas in the definition of the stages of CKD in 882 subjects with different clinical situations over a wide range of glomerular filtration rates (GFRs) (4.2-173.7 mL/min).

Results

Misclassification was a constant for all 61 formulas evaluated and averaged 50% for creatinine-based and 35% for cystatin C-based equations. Most of the cases were misclassified as one stage higher or lower. However, in 10% of the subjects, one stage was skipped and patients were classified two stages above or below their real stage. No clinically relevant improvement was observed with cystatin C-based formulas compared with those based on creatinine.

Conclusions

The error in the classification of CKD stages by formulas was extremely common. Our study questions the reliability of both cystatin C and creatinine-based formulas to correctly classify CKD stages. Thus the correct classification of CKD stages based on estimated GFR is a matter of chance. This is a strong limitation in evaluating the severity of renal disease, the risk for progression and the evolution of renal dysfunction over time.

Estimated GFR: time for a critical appraisal

Since 1957, over 70 equations based on creatinine and/or cystatin C levels have been developed to estimate glomerular filtration rate (GFR). However, whether these equations accurately reflect renal function is debated. In this Perspectives article, we discuss >70 studies that compared estimated GFR (eGFR) with measured GFR (mGFR), involving ~40,000 renal transplant recipients and patients with chronic kidney disease (CKD), type 2 diabetes mellitus or polycystic kidney disease. Their results show that eGFR often differed from mGFR by ±30% or more, that eGFR values incorrectly staged CKD in 30-60% of patients, and that eGFR and mGFR gave different rates of GFR decline. Errors were unpredictable, and comparable for equations based on creatinine and/or cystatin C. We argue, therefore, that the persistence of these errors (despite intensive research) suggests that the problem lies with using creatinine and/or cystatin C as markers of renal function, rather than with the mathematical methods used for GFR estimation.

The Error of Estimated GFR in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus represents 30-50% of the cases of end stage renal disease worldwide. Thus, a correct evaluation of renal function in patients with diabetes is crucial to prevent or ameliorate diabetes-associated kidney disease. The reliability of formulas to estimate renal function is still unclear, in particular, those new equations based on cystatin-C or the combination of creatinine and cystatin-C. We aimed to assess the error of the available formulas to estimate glomerular filtration rate in diabetic patients. We evaluated the error of creatinine and/or cystatin-C based formulas in reflecting real renal function over a wide range of glomerular filtration rate (from advanced chronic kidney disease to hyperfiltration). The error of estimated glomerular filtration rate by any equation was common and wide averaging 30% of real renal function, and larger in patients with measured glomerular filtration rate below 60 mL/min. This led to chronic kidney disease stages misclassification in about 30% of the individuals and failed to detect 25% of the cases with hyperfiltration. Cystatin-C based formulas did not outperform creatinine based equations, and the reliability of more modern algorithms proved to be as poor as older equations. Formulas failed in reflecting renal function in type 2 diabetes mellitus. Caution is needed with the use of these formulas in patients with diabetes, a population at high risk for kidney disease. Whenever possible, the use of a gold standard method to measure renal function is recommended.

[Kidney function and liver transplantation]

INTRODUCTION

In liver cirrhosis renal function decreases as well. Hepatorenal syndrome is the most frequent cause of the decrease, but primary kidney failure, diabetes mellitus and some diseases underlying endstage liver failure (such as hepatitis C virus infection) can also play an important role. In liver transplantation several further factors (total cross-clamping of vena cava inferior, polytransfusion, immunosuppression) impair the renal function, too.

AIM

The aim of this study was to analyse the changes in kidney function during the first postoperative year after liver transplantation.

METHOD

Retrospective data analysis was performed after primary liver transplantations (n = 319).

RESULTS

impaired preoperative renal function increased the devepolment of postoperative complications and the first year cumulative patient survival was significantly worse (91,7% vs 69,9%; p<0,001) in this group. If renal function of the patients increased above 60 ml/min/1,73 m2 after the first year, patient survival was better. Independently of the preoperative kidney function, 76% of the patients had impaired kidney function at the first postoperative year. In this group, de novo diabetes mellitus was more frequently diagnosed (22,5% vs 9,5%; p = 0,023).

CONCLUSIONS

Selection of personalized immunosuppressive medication has a positive effect on renal function.

Comparative performance of four equations estimating glomerular filtration rate in adult Chinese diabetics

BACKGROUND

The Cockcroft-Gault equation, abbreviated Modification of Diet in Renal Disease (MDRD) equation, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and improved abbreviated MDRD equation were used to evaluate renal function in diabetic patients. However, little is known regarding their applicability and precision in Chinese diabetic patients.

AIM

To compare the accuracy of four methods evaluating Chinese diabetic patients' renal function.

MATERIALS AND METHODS

This study included 329 Chinese diabetic patients. Standard GFR (sGFR) was measured via ⁹⁹mTc-DTPA dynamic renal imaging. Estimated GFR (eGFR) was calculated by four equations separately. Applicability of these four equations in Chinese diabetic patients was determined by correlation studies, agreement test, and receiver operating characteristic (ROC) curves.

RESULTS

For Chinese diabetic patients, four methods assessing eGFR correlated well with sGFR. Overall, eGFR calculated via improved abbreviated MDRD had less bias and greater accuracy than the other algorithms estimating GFR (p ≤ 0.01). For patients with sGFR ≥ 60 ml/min/1.73 m², all four equations significantly underestimated actual GFR, with the improved abbreviated MDRD equation best approximating actual GFR (p ≤ 0.01). Conversely, in patients with sGFR<60 ml/min/1.73 m², all four equations overestimated actual GFR; GFR(improved MDRD) was relatively the most accurate (p ≤ 0.01).

CONCLUSIONS

While all four equations were inaccurate, the improved abbreviated MDRD equation best diagnosed and stratified renal failure in Chinese diabetic patients.

Simple cystatin C formula for estimation of glomerular filtration rate in overweight patients with diabetes mellitus type 2 and chronic kidney disease

In clinical practice the glomerular filtration rate (GFR) is estimated from serum creatinine-based equations like the Cockcroft-Gault formula (C&G) and Modification of Diet in Renal Disease formula (MDRD). Recently, serum cystatin C-based equations, the newer creatinine formula (The Chronic Kidney Disease Epidemiology Collaboration formula (CKD-EPI)), and equation that use both serum creatinine and cystatin C (CKD-EPI creatinine & cystatin formula) were proposed as new GFR markers. Present study compares serum creatinine-based equations, combined (including both serum creatinine and cystatin C) equation, and serum simple cystatin C formula (100/serum cystatin C) against 51CrEDTA clearance in 113 adult overweight Caucasians with diabetes mellitus type 2 (DM2) and chronic kidney disease (CKD). The results of present study demonstrated that the simple cystatin C formula could be a useful tool for the evaluation of renal function in overweight patients with DM2 and impaired kidney function in daily clinical practice in hospital and especially in outpatients. Despite the advantages of the simple cystatin C formula, cystatin C-based equations cannot completely replace the "gold standard" for estimation of the GFR in a population of DM2 patients with CKD, but may contribute to a more accurate selection of patients requiring such invasive and costly procedures.

Comparative evaluation of the Cockcroft-Gault Equation and the Modification of Diet in Renal Disease (MDRD) study equation for drug dosing: an opinion of the Nephrology Practice and Research Network of the American College of Clinical Pharmacy

Accurate assessment of kidney function is an important component of determining appropriate drug dosing regimens. Nearly all manufacturer-recommended dosage adjustments are based on creatinine clearance ranges derived from clinical pharmacokinetic studies performed during the drug development process. The Cockcroft-Gault (CG) equation provides an estimate of creatinine clearance and is the equation most commonly used to determine drug dosages in patients with impaired kidney function. The Modification of Diet in Renal Disease (MDRD) study equation has also been proposed for this purpose. Published studies report that drug dosages determined by the two equations do not agree in 10-40% of cases. However, interpretation and comparison of these studies are complicated by the variable creatinine methods used for calculating CG and MDRD estimates, the patient populations studied, and a lack of outcomes data demonstrating the clinical significance of dosing discrepancies. Moreover, the impact of reporting standardized serum creatinine values on the accuracy of the CG equation and corresponding drug dosing regimens have been questioned. Currently, no prospective pharmacokinetic studies have been conducted with use of the MDRD equation to generate dosing recommendations, and limited data are available to support its use in some patient populations representing demographic extremes. Collectively, these issues have resulted in considerable confusion among clinicians and have fueled a healthy debate on whether or not to use the MDRD equation to determine drug dosages. Each of these issues is reviewed, and a proposed algorithm for using creatinine-based kidney function assessments in drug dosing is provided. Knowledge of the advantages, limitations, and clinical role of each equation will facilitate their safe and effective use in drug dosing.

Predictive performance of 12 equations for estimating glomerular filtration rate in severely obese patients

ABSTRACT Objective: Considering that the Cockcroft-Gault formula and the equation of diet modification in renal disease are amply used in clinical practice to estimate the glomerular filtration rate, although they seem to have low accuracy in obese patients, the present study intends to evaluate the predictive performance of 12 equations used to estimate the glomerular filtration rate in obese patients. Methods: This is a cross-sectional retrospective study, conducted between 2007 and 2008 and carried out at a university, of 140 patients with severe obesity (mean body mass index 44 ± 4.4 kg/m2). The glomerular filtration rate was determined by means of 24-hour urine samples. Patients were classified into one or more of the four subgroups: impaired glucose tolerance (n = 43), diabetic (n = 24), metabolic syndrome (n = 76), and/or hypertension (n = 66). We used bias, precision, and accuracy to assess the predictive performance of each equation in the entire group and in the subgroups. Results: In renal disease, Cockcroft-Gault's formula and the diet modification equation are not precise in severely obese patients (precision: 40.9 and 33.4, respectively). Sobh's equation showed no bias in the general group or in two subgroups. Salazar-Corcoran's and Sobh's equations showed no bias for the entire group (Bias: −5.2, 95% confidence interval (CI) = −11.4, 1.0, and 6. 2; 95%CI = −0.3, 12.7, respectively). All the other equations were imprecise for the entire group. Conclusion: Of the equations studied, those of Sobh and Salazar-Corcoran seem to be the best for estimating the glomerular filtration rate in severely obese patients analyzed in our study.

Estimation of renal function in patients with diabetes

Diabetes is the leading cause of chronic kidney disease (CKD), which makes estimation of renal function crucial. Serum creatinine is not an ideal marker of glomerular filtration rate (GFR), which also depends on digestive absorption, and the production of creatinine in muscle and its tubular secretion. Formulas have been devised to estimate GFR from serum creatinine but, given the wide range of GFR, proteinuria, body mass index and specific influence of glycaemia on GFR, the uncertainty of these estimations is a particular concern for patients with diabetes. The most popular recommended formulas are the simple Cockcroft-Gault equation, which is inaccurate and biased, as it calculates clearance of creatinine in proportion to body weight, and the MDRD equation, which is more accurate, but systematically underestimates normal and high GFR, being established by a statistical analysis of results from renal-insufficient patients. This underestimation explains why the MDRD equation is repeatedly found to give a poor estimation of GFR in patients with recently diagnosed diabetes and is a poor tool for reflecting GFR decline when started from normal, as well as the source of unexpected results when applied to epidemiological studies with a 60mL/min/1.73m(2) threshold as the definition of CKD. The more recent creatinine-based formula, the Mayo Clinic Quadratic (MCQ) equation, and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) improve such underestimation, as both were derived from populations that included subjects with normal renal function. Determination of cystatin C is also promising, but needs standardisation.

Assessment of glomerular filtration rate by serum cystatin C in patients undergoing coronary artery bypass grafting

BACKGROUND

Assessment of renal function in patients undergoing coronary artery bypass grafting (CABG) is important. Cystatin C has been proposed as an improved indicator of renal function. The aim of this study was to assess cystatin C as an early marker of changes in glomerular filtration rate (GFR) after CABG.

METHODS

Blood samples were collected from 61 CABG patients at different time points. Using (51)Cr-ethylenediaminetetraacetic acid ((51)Cr-EDTA) clearance as a 'gold standard', we compared the correlations and non-parametric receiver operator characteristic curves of serum cystatin C, serum creatinine and 24 h creatinine clearance (Ccr).

RESULTS

The inverse of cystatin C correlated better with (51)Cr-EDTA than those of serum creatinine and Ccr (r = 0.8578, 0.6771 and 0.6929, respectively). Cystatin C exhibited significantly superior diagnostic accuracy for detecting GFR <80 mL/min/1.73 m(2) compared with serum creatinine (P = 0.013) and Ccr (P = 0.025); for detecting GFR <60 mL/min/1.73 m(2), cystatin C had similar diagnostic accuracy to Ccr (P = 0.812) but was superior to creatinine (P = 0.033). At the best cut-off value, cystatin C had sensitivity 89% and specificity 93% for detecting GFR <80 mL/min/1.73 m(2), sensitivity 86% and specificity 96% for detecting GFR <60 mL/min/1.73 m(2).

CONCLUSIONS

Cystatin C is a better marker for detecting small temporary changes of GFR in CABG patients. This may allow better identification of patients with renal impairment.

Cystatin C improves the diagnosis and stratification of chronic kidney disease, and the estimation of glomerular filtration rate in diabetes

AIMS

Estimation of glomerular filtration rate (GFR) is recommended to diagnose and stratify chronic kidney disease (CKD). Can cystatin-C (cysC) assay improve the results in diabetic patients?

METHODS

In 124 diabetic patients with a wide range of GFR, as determined by 51Cr-EDTA clearance (i-GFR), we estimated 'e-GFR' by: the recommended Cockcroft-Gault (CG) formula and Modification of Diet in Renal Disease (MDRD) study equation; the new Mayo Clinic quadratic (MCQ) equation; the recently proposed composite estimation including both serum creatinine and cysC; and a simplified approach dividing the MDRD by cysC if less than 1.10mg/L.

RESULTS

The highest diagnostic accuracy (receiver operating characteristic [ROC] curves) and the highest proportions of well-stratified patients were obtained by cysC and the MDRD which, however, underestimated i-GFR for patients without CKD (-17%, P<0.001). The CG overestimated GFR in KDOQI stages 1 and 2, ignored stage 5 and was the least accurate. The MCQ equation overrepresented stage 2, overestimating GFR at this stage (+23%, P<0.005). The composite estimation (54.7+/-27.0mL per minute 1.73m(2)) correlated best with i-GFR (56.1+/-35.3; r=0.90, P<0.001), and did not significantly differ from it across the entire population and within each Kidney Disease Outcome Quality Initiative (KDOQI) stage but was also biased (Bland-Altman procedure). Simply dividing the MDRD by cysC ifless than1.10mg/L produced a comparable performance and eliminated the bias.

CONCLUSION

The recommended creatinine-based estimations of GFR need to be improved. CysC assay helps in the diagnosis and stratification of CKD and leads to better estimates of GFR in diabetic patients without any substantial increase in complexity.