Cystatin C as a marker of renal function immediately after liver transplantation

To verify whether cystatin C may be of some use as a renal function marker immediately after orthotopic liver transplantation (OLT), we compared serum cystatin C (S(Cyst)), serum creatinine (S(cr)), and creatinine clearance (C(cr)) levels with the glomerular filtration rate (GFR). On postoperative days 1, 3, 5, and 7, S(Cyst) and S(cr) was measured in simultaneously drawn blood samples, whereas C(cr) was calculated using a complete 24-hour urine collection. The GFR was determined on the same days by means of iohexol plasma clearance (I-GFR). The correlation between 1/S(Cyst) and I-GFR was stronger than that of 1/S(cr) or C(cr) (P< 0.01). In the case of moderate reductions in I-GFR (80-60 mL/minute/1.73 m), S(cr) remained within the normal range, whereas the increase in S(cyst) was beyond its upper limit; for I-GFR reductions to lower levels (59-40 mL/minute/1.73 m), S(cr) increased slightly, whereas S(cyst) was twice its upper normal limit. When we isolated all of the I-GFR values on days 3, 5, and 7 that were > or = 30% lower than that recorded on the first postoperative day, S(Cyst)(P< 0.0001) and S(cr) (P< 0.01) levels were increased, whereas C(cr) remained unchanged (P = 0.09). Receiver operating characteristic (ROC) area-under-the-curve analysis showed that the diagnostic accuracy of S(cyst) was better than that of S(cr) and C(cr). S(cyst) levels of 1.4, 1.7, and 2.2 mg/L respectively predicted I-GFR levels of 80, 60, and 40 mL/minute/1.73 m. In conclusion, cystatin C is a reliable marker of renal function during the immediate post-OLT period, especially when the goal is to identify moderate changes in GFR.