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 β-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 eGFRβTP (b = 0.414, p = 0.0002) and a negative relationship with eGFRcys (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.