Serum cystatin C and beta2-microglobulin as markers of glomerular filtration rate.

Continuous efforts have been made to find out precise and simple method for determination of glomerular filtration rate (GFR). Cystatin C (cysteine proteinase inhibitor = CyC) is a low molecular weight (LMW) protein which is produced constantly by all nucleated cells independently of different pathological conditions and eliminated from the blood exclusively by glomeruli. So, CyC closely reflects the GFR. In the present study 75 patients aged between 18 and 74 (44.3 +/- 12.2) years were analyzed, with the aim to compare the reciprocal values of serum level of LMW proteins CyC and beta2-microglobulin (beta2-MG) with creatinine clearance (Ccr) as a measure of GFR. Patients were divided into groups according to sex, age (<60; >60 years) and renal diseases: patients with glomerulonephritis (GN) with and without nephrotic proteinuria, pyelonephritis (PyN), and renal transplant (Tx). High correlation between Ccr and 1/CyC (r = 0.81; p < 0.01) and Ccr and 1/beta2-MG (r = 0.80; p < 0.01) in all examined patients was found. There was significant correlation between Ccr and 1/CyC (0.82 vs. 0.79) and Ccr and 1/beta2-MG (0.85 vs. 0.76) in men as well in women, and also in two groups of patients formed according to the age (0.82 vs. 0.77; p < 0.01; 0.80 vs. 0.81; p < 0.01), without any statistical significant difference between the groups. In studied groups with different renal diseases, there were no differences in correlation coefficients between Ccr and 1/CyC and Ccr and 1/beta2-MG (p1 = 0.29; p2 = 0.21; p3 = 0.79; p4 = 0.43), without statistical differences between the groups, except significant difference in correlation coefficients for Ccr and 1/beta2-MG between patients with GN with and without nephrotic proteinuria (p < 0.032). LMW proteins, serum CyC and beta2-MG, are as good markers of GFR as Ccr, regardless sex and age. Both of these LMW proteins are good markers of GFR in patients with GN without nephrotic proteinuria, PyN and Tx patients. In patients with GN and nephrotic proteinuria serum CyC is a better marker of GFR than beta2-MG.