Estimated glomerular filtration rate in the nephrotic syndrome

Background. Plasma creatinine concentration and creatinine-based equations are most commonly used as markers of glomerular filtration rate (GFR). The abbreviated MDRD formula is considered the best available formula. Altered renal handling of creatinine, which may occur in the nephrotic syndrome, will invalidate creatinine-based formulas. We have evaluated the abbreviated MDRD formula in a large cohort of patients with proteinuria. Methods. Data on a cohort of patients with glomerular diseases were available from a large database. We have studied the relationship between estimated GFR (MDRD formula), and plasma cystatin C (CysC) and plasma beta-2- microglobulin (beta 2m) as markers of GFR. Results. The final analysis included 142 patients (93 M/49 F), median age 48 years (+/- 15), plasma creatinine 101 mu mol/L (42-368), plasma albumin 28.0 g/L (10.0-47.0), proteinuria 6.4 g/day (0.03-37.9), eGFR-MDRD4 64 mL/min/1.73 m(2) (15-165), beta 2m 3.43 mg/L (0.7-13.8) and CysC 1.14 mg/mL (0.56-4.00). As expected, we observed a hyperbolic relationship between eGFR and both beta 2m and CysC. In multivariable analysis, plasma albumin concentration proved to be the most important predictor of the relationship between eGFR and both CysC and beta 2m. In the presence of hypoalbuminaemia, eGFR was similar to 30-40% higher at equal levels of plasma CysC or beta 2m. Conclusions were similar when using the recently developed CKD-EPI formula. Plasma albumin concentration did not effect the relationship between eGFR estimated by the six-variable original MDRD formula and beta 2m. Conclusions. Our data point to discrepancies between eGFR using the six-variable MDRD formula and eGFR using the abbreviated MDRD formula as well as the CKD-EPI formula in patients with hypoalbuminaemia. One should be aware of possible limitations of creatinine-based eGFR formulas in patients with a nephrotic syndrome.