β-Trace Protein, Cystatin C, β2-Microglobulin, and Creatinine Compared for Detecting Impaired Glomerular Filtration Rates in Children

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Abstract
Background: Because of the limitations of serum creatinine as a marker of glomerular filtration rate (GFR) in children, we assessed the diagnostic accuracy of the novel marker β-trace protein (BTP) in comparison with cystatin C (Cys-C), β2-microglobulin (β2-MG), and creatinine as conventional indicators of reduced GFR. Methods: We obtained serum samples from 225 children (age range, 0.2–18 years) with various renal pathologies who were referred for nuclear medicine clearance investigations (technetium-diethylenetriamine pentaacetic acid or chromium-EDTA). We measured Cys-C, BTP (nephelometric tests; Dade Behring), β2-MG (Tinaquant; Roche), and creatinine (enzymatic assay; Creatinine-PAP; Roche). Results: Seventy-five children had reduced GFR (90 mL · min−1 · 1.73 m−2 comprised the control group with gaussian distributions of BTP and Cys-C concentrations. The upper reference limits (97.5 percentile) were 1.01 mg/L for BTP and 1.20 mg/L for Cys-C. The correlations of nuclear medicine clearance with the reciprocals of BTP, Cys-C, and the Schwartz GFR estimate were significantly higher (r = 0.653, 0.765, and 0.706, respectively; P <0.05) than with the reciprocal of creatinine or β2-MG (r = 0.500 and 0.557, respectively). ROC analysis showed a significantly higher diagnostic accuracy of BTP, Cys-C, and the GFR estimate for the detection of impaired GFR than serum creatinine (P <0.05). Compared to creatinine, BTP increased the diagnostic sensitivity by ∼30%, but it was not more sensitive than Cys-C or the Schwartz GFR estimate. Conclusions: BTP is superior to serum creatinine and an alternative for Cys-C to detect mildly reduced GFR in children, but it is not better than the Schwartz GFR estimate.