Cystatin C - plasma or serum

5 mL blood in lithium heparin or plain tube.

1-18 years: 0.5-1.3 mg/L
Adults: 0.5-1.0 mg/L.

Cystatin C can be used for the diagnosis of impaired renal function. The reciprocal of the serum cystatin C concentration has been shown in several studies to have a better correlation to GFR than serum creatinine. In addition, significant increase in serum creatinine is not detected until after the GFR has fallen by 50 percent.

Cystatin C provides a good means of evaluating renal function in pediatric patients because it declines from neonatal levels to near adult values by one year of age.