Beta-trace protein is not superior to cystatin C for the estimation of GFR in patients receiving corticosteroids

Objectives: Comparison of the effect of corticosteroid therapy on the diagnostic performance of cystatin C (Cys) and beta-trace protein (bTP), two endogenous markers of GFR. Design and methods: Out of a total of 193 pediatric inulin clearance studies, a random sample of 85 steroid-free studies served to establish GFR prediction equations (eGFR), which were used to compare the remaining 76 steroid-free and 32 steroid-positive studies (median prednisone dose 33.0 mg m(-2) day(-1)). Results: We found a positive relationship between prednisone dose and eGFR(beta TP) (b=0.414, p=0.0002) and a negative relationship with eGFR(cys) (b=-0.208, p=0.0091). Only Cys independently predicted GFR below 90 mL min(-1) 1.73 m(-2), both in steroid-positives (b=6.260, p=0.010) and steroid-negatives (b=6.845, p=0.012). Glucocorticoid therapy did not affect the accuracy in estimating GFR within 30% of measured GFR for Cys, while accuracy was lower with bTP (65.6% vs. 81.6%, p=0.08). Conclusion: Glucocorticoids have less impact on the diagnostic accuracy of Cys than bTP. (C)0 2007 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.