Cystatin C, Serum
Collect SST/1 mL serum. After 30 minutes of clotting, promptly centrifuge and send refrigerated.
Room temp: Unacceptable, Refrigerated: 7 days, Frozen: 3 months
1-3 days Performed Sunday-Thursday
Since it is formed at a constant rate and freely filtered by the healthy kidney, cystatin C is a good marker of renal function.