Effect of clinical variables and immunosuppression on serum cystatin C and beta-trace protein in kidney transplant recipients.

BACKGROUND: Cystatin C and beta-trace protein (BTP) are low-molecular-weight proteins that have generated interest as alternative endogenous markers of glomerular filtration rate (GFR). Studies examining the effect of demographic, biometric, clinical, and biochemical variables on cystatin C levels have yielded conflicting results, perhaps because of the reliance on inferior methods of GFR determination. The aim of this study is to examine the independent effect of various clinical parameters on serum concentrations of creatinine, cystatin C, and BTP in kidney transplant recipients.

STUDY DESIGN: Cross-sectional study.

SETTING & PARTICIPANTS: 207 kidney transplant recipients with stable kidney function.

PREDICTORS: GFR, age, race, sex, body mass index, albumin level, proteinuria, smoking status, prednisone, and calcineurin inhibitor and mycophenolate mofetil use.

OUTCOMES & MEASUREMENTS: Multiple linear regression analysis was used to examine the relationship between predictor variables and cystatin C, BTP, and creatinine levels. GFR was measured by using technetium 99m-radiolabeled diethylenetriaminepentaacetic acid clearance.

RESULTS: After adjusting for GFR, cystatin C and BTP levels were significantly lower in women compared with men. Greater albumin concentration was associated with significantly lower cystatin C and BTP concentrations. There was a statistically significant, but clinically small, association between body mass index and cystatin C level, but no association between the other demographic variables or medications analyzed.

LIMITATIONS: Predominantly white population; results may not be applicable to other racial groups.

CONCLUSION: Important nonrenal factors can influence BTP and cystatin C concentrations and need to be considered when interpreting BTP and cystatin C values in kidney transplant patients.