Estimated creatinine clearance is not an accurate index of glomerular filtration rate in normoalbuminuric diabetic patients

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.

An Alternative Formula to the Cockcroft-Gault and the Modification of Diet in Renal Diseases Formulas in Predicting GFR in Individuals with Type 1 Diabetes

Chronic kidney disease is currently on the rise and not only leads to ESRD necessitating dialysis or transplantation but also increases cardiovascular disease risk. Measurement of the GFR, the gold standard for assessing kidney function, is expensive and cumbersome. Several prediction formulas that are based on serum creatinine are currently used to estimate the GFR, but none has been validated in a large cohort of individuals with diabetes. The performance of two commonly used formulas, the abbreviated Modification of Diet in Renal Disease (MDRD) study formula for the GFR and the Cockcroft-Gault estimate of creatinine clearance, were examined against GFR measured by the renal clearance of iothalamate in 1286 individuals with type 1 diabetes from the Diabetes Control and Complications Trial (DCCT). The performance of these formulas was assessed by computing bias, precision, and accuracy. The DCCT participants had normal serum creatinine, unlike the MDRD patients, and somewhat lower creatinine excretion than subjects in the original cohort Cockcroft Gault, which led to biased and highly variable estimates of GFR when these formulas were applied to the DCCT subjects. The MDRD substantially underestimated iothalamate GFR, whereas the Cockcroft Gault formula underestimated it when it was <120 ml/min per 1.73 m(2) and overestimated it when iothalamate GFR was >130 ml/min per 1.73 m(2). Overall, only one third of the formula's estimates were within +/-10% of iothalamate GFR. By underestimating GFR, these formulas were likely to flag early declines in kidney function. Refitting the MDRD formula to the DCCT data gave a more accurate and unbiased prediction of GFR from serum creatinine; percentage of estimate within 10% of measured GFR increased to 56%. A substantial variability in the estimates, however, remained.

Predictive performance of ten equations for estimating creatinine clearance in cardiac patients. Iohexol Cooperative Study Group

OBJECTIVE

The predictive performance of 10 equations used to estimate creatinine clearance (Clcr) was assessed retrospectively from data collected on 420 patients.

DESIGN

This study is a retrospective data analysis of information collected on hemodynamically stable patients awaiting coronary angiography during the Iohexol Cooperative Study.

SETTING

The Iohexol Cooperative Study was a multicenter study that compared nephrotoxicity of high- and low-osmolar contrast media in patients undergoing coronary angiography. Data used for this analysis were preangiography 24-hour urine collections that were primarily collected in hospitalized patients.

PATIENTS

Patients selected from the Iohexol Cooperative Study database for analysis were participants categorized into one or more of six subgroups: elderly (n = 222), hypoalbuminemic (n = 25), chronic renal insufficiency (n = 128), low serum creatinine (n = 115), obese (n = 208), and diabetic (n = 191) who had baseline urine collections of at least 24 hours.

OUTCOME MEASURES

Predictive performance was assessed using bias, precision, slopes, and y-intercepts.

RESULTS

The Salazar-Corcoran equation was unbiased in the entire group as well as in five of the subgroups. The Cockcroft-Gault equation was unbiased in three of the subgroups. All other equations were biased in predicting Clcr in the entire group as well as in at least four of the subgroups. Precision was generally poor. All slopes were significantly different than one and all y-intercepts were significantly different than zero (p < 0.01). Correlation coefficients were between 0.63 and 0.79 with the exceptions of the low serum creatinine subgroup (r values 0.35-0.64) and the Davis-Chandler equation (r values 0.35-0.71 across groups).

CONCLUSIONS

Of the equations studied, Salazar-Corcoran and Cockcroft-Gault appear to be the best for predicting Clcr.

Monitoring kidney function in diabetic nephropathy

Progression in diabetic nephropathy is usually determined by repeated measurements of glomerular filtration rate and expressed as rate of decline in glomerular filtration rate. Our aim was to evaluate the agreement between rate of decline in glomerular filtration rate estimated from the Cockroft-Gault formula: (140-age)*K*body weight*(1/S-creatinine) and measured by the plasma clearance of 51Cr-EDTA. All insulin-dependent diabetic patients with diabetic nephropathy followed-up for at least 5 years with at least 5 simultaneous measurements of glomerular filtration rate, s-creatinine, and weight were included in the study. Forty-three patients (32 male/11 female), age 31 (18-61) years were enrolled. Observation period: 6.6 (5.1-9.9) years and number of investigations per patient 6 (5-16) (median(range)). Baseline glomerular filtration rate (ml/min) was 97 (30) measured and 107 (37) estimated (mean(SD))(p < 0.001) and the 95% limits of agreement were -42.0 to 20.8 ml/min. Measured and estimated glomerular filtration rate correlated significantly (r = 0.91, p < 0.00001). Rate of decline in kidney function ml.min-1.year-1 was 4.7 (3.3) measured and 4.8 (3.5) estimated (mean(SD)) (NS), but the 95% limits of agreement showed a wide range -3.9 to 3.5 ml.min-1.year-1. A significant correlation between rate of decline in measured and estimated glomerular filtration rate was present (r = 0.84, p < 0.00001). In conclusion, glomerular filtration rate is overestimated by the Cockroft-Gault formula. The mean rates of decline in glomerular filtration rate are comparable, but the limits of agreement are wide, which make the Cockroft-Gault method unacceptable for clinical purposes, i.e. monitoring progression in kidney function in the individual patient.(ABSTRACT TRUNCATED AT 250 WORDS)