Serum Cystatin C Is a Better Marker for Renal Function Than Serum Creatinine in Children with Sickle Cell Disease.

High serum creatinine is a late manifestation for patients (pts) with sickle cell disease (SCD) who develop severe renal dysfunction, because creatinine is secreted by the renal tubules. Serum cystatin C is a cysteine proteinase inhibitor, that is produced by all nucleated cells in the body, does not undergo tubular secretion, and reflects glomerular filtration rate (GFR)accurately. Normal levels for serum cystatin C are 0.5–1.3 mg/L for children 1–17 years, and 0.5–1 mg/L for adults. The purpose of this study was to compare serum cystatin C and serum creatinine as markers of GFR in children with SCD with different levels of albuminuria. Twenty pts (mean age 16.4, range 9–21 years) had serum creatinine, serum cystatin, and 24-hour urine for creatinine clearance. Pts with normoalbuminuria (N=11) had mean serum creatinine of 0.55±0.14 mg/L, creatinine clearance of 168±36 ml/min/1.73m², normal serum cystatin C 0.78±0.16 mg/L, and normal estimated GFR derived from cystatin of 106±27 ml/min/1.73m². In contrast, pts with proteinuria (N=4) had higher or abnormal serum cystatin C (mean 1.25 ±0.34, range 0.9–1.7 mg/L) and reduced estimated GFR (mean 59±21, range 35–85) consistent with poor kidney function; nevertheless, the serum creatinine (0.7±0.2) and creatinine clearance remained normal (125±27). Pts with only microalbuminuria (N=5) maintained normal levels of cystatin C and estimated GFR by cystatin. We conclude that serum cystatin C discriminated better for kidney dysfunction than serum creatinine and creatinine clearance with significantly different values between patients with normoalbuminuria and macroalbuminuria (p=0.038). More studies are warranted in order to investigate further the value of serum cystatin C in the monitoring of patients with SCD and albuminuria.