RESUMEN
Nephrotic syndrome [NS] is the most common chronic renal disease of childhood. The rapid and accurate evaluation of renal function is important to detect the extent and progress of renal affection. Glomerular filtration rate [GFR] is the best marker for renal function. Serum cystatin C; a cysteine proteinase inhibitor; has been proposed as a sensitive marker for GFR. Our study was conducted on 50 patients with NS [23 with minimal change disease 'MCD', 12 with focal segmental glomerulosclerosis 'FSGS' and 15 with mesangioproliferative glomerulonephritis 'MP'], as well as 20 age and sex matched normal controls. In addition to routine assessment, creatinine clearance and serum cystatin C were measured in a trial to evaluate the importance of serum cystatin C versus serum creatinine in the detection of early impairment of renal function. Our results showed a significant 'positive' correlation between the creatinine clearance and the 'reciprocals' of both serum cystatin C and serum creatinine in all the 70 studied cases [P<0.0005]. The correlation was significantly better for serum cystatin C [r = 0.879] than the serum creatinine [r = 0.776]. Also serum cystatin C was significantly higher in nephrotic patients than in controls [P < 0.0005] while the serum creatinine was less significantly elevated [P < 0.05]. Mean while, serum cystatin C showed higher negative and positive predictive values [95% and 92% respectively] as compared to serum creatinine [88% and 76% respectively] in the detection of impairment of GFR, denoting the ability of serum cystatin C to detect the early changes in renal function. The reference interval of serum cystatin C as measured in our controls was independent on age or sex, and ranged between 0.6-1.32 mg/L. The highest diagnostic accuracy [95.7%] was obtained when the upper limit of 1.43 mg/L was used. So we could conclude that serum cystatin C is more sensitive and specific than serum creatinine in the detection of early impairment of GFR