CYSTATIN-C MEASUREMENT AND ITS PRACTICAL USE IN PATIENTS WITH VARIOUSRENAL DISEASES

Objective: To evaluate the clinical usefulness in terms of estimation for glomerular filtration rate (GFR), we determined the cystatin C lev els in the serum and urine of 33 healthy volunteers as well as in the serum and urine of 35 patients with various renal diseases and compare d them with those of creatinine. In addition, we evaluated this substa nce as an indicator of removal rate of low molecular weight protein wi th high flux membranes in 6 hemodialysis (HD) patients. Methods: Serum and urinary cystatin C levels were measured by using an enzyme-linked immunosorbent assay (ELISA) method. 24-hour creatinine clearance was used as an indicator of GFR. Results: Reference intervals with 95% ran ges are 0.47-1.03 mg/l in the serum from healthy volunteers, There was a significant positive correlation between serum cystatin C and creat inine levels (r = 0.936, p <0.001) in the patients with various renal diseases, Serum cystatin C and creatinine inversely and logarithmicall y correlated to creatinine clearance as shown in the following equatio ns: log cystatin C = -0.564 x log creatinine clearance + 1.216 (r = -0 .850), log creatinine = -0.678 x log creatinine clearance + 1.449 (r = -0.904). In these equations l/day is the unit used for creatinine cle arance, mg/l is the unit used for serum cystatin C, The range for cyst atin C is 0.67-6.15 mg/l, 0.66-7.23 mg/dl for creatinine and 8.9-186.3 l/day (6.2-129.4 ml/min) for creatinine clearance. Serum cystatin C l evels started to increase over normal range when creatinine clearance fell below 135.9 l/day (94.4 ml/min), while serum creatinine remained within normal ranges. The daily urinary excretion of cystatin C was in creased significantly in the group in which creatinine clearance was b elow 30 l/day (20.8 ml/min) compared to that in which creatinine clear ance was higher than in 70 l/day (48.6 ml/min), Fractional clearance o f cystatin C increased proportionally and markedly to the decrease of creatinine clearance. In a regular HD condition with high flux membran e, the cystatin C removal rate was 38.7 +/- 1.7%. Conclusions: These d ata suggest that combined measurement of cystatin C in the serum and u rine is useful to estimate GFR, especially to detect the mild reductio n of GFR, Cystatin C measurement can also be used as an indicator of r emoval rate of low molecular weight protein with different types of hi gh flux membranes in hemodialysis.