Adult reference ranges for serum cystatin C, creatinine and predicted creatinine clearance

Serum cystatin C measurement has been previously shown by ourselves and others to be a better indicator of changes in glomerular filtration rate (GFR) than serum creatinine. However, the available literature on reference values for cystatin C concentration remains surprisingly sparse; we thus set out to determine an adult reference range. Blood was taken from 309 healthy blood donors and creatinine and cystatin C concentrations were measured using commercially available automated methodologies. In addition, predicted creatinine clearances were calculated using the Cockcroft and Gault formula. The 95% reference intervals for creatinine, predicted creatinine clearance and cystatin C for all blood donors, regardless of gender, were 68-118 µmol/L, 58-120 ml/min/1·73 m 2 and 0·51-0·98 mg/L, respectively. For women, the intervals were 68-98 µmol/L, 60-119 ml/min/1·73 m 2 and 0·49-0·94 mg/ L; for men, they were 78-123 µmol/L, 57-122 ml/min/1·73 m 2 and 0·56-0·98 mg/L. The mean 95% reference interval for cystatin C in all donors under 50 years of age was 0·53-0·92 mg/L; for those over 50 years of age it was 0·58-1·02 mg/L. The small difference between male and female ranges meant that a single reference range for cystatin C could be established for all adults under 50 years of age without adjustment for body surface area. Serum cystatin C measurement offers a simpler and more sensitive screening test than serum creatinine for early changes in GFR.