Evaluating the diagnostic value of rescaled β-trace protein in combination with serum creatinine and serum cystatin C in older adults

Background: Beta trace protein (BTP) is a novel renal biomarker that has emerged as potential alternative or addition to serum creatinine (Scr) and serum cystatin C (ScysC). We analyzed BTP's diagnostic ability to detect impaired kidney function by rescaling it and we tested whether rescaling BTP allowed us to expand the Full-Age-Spectrum (FAS)-equation to BTP.

Methods: 566 participants aged ≥70 years with measured glomerular filtration rate (mGFR), Scr, ScysC and BTP from the population-based Berlin Initiative Study (BIS) were considered. We developed a single and combined FAS-equation using rescaled BTP (BTP/0.60) and calculated its sensitivity (S) and specificity (Sp) to identify kidney disease using a fixed (60 mL/min/1.73 m²) and age-dependent threshold for mGFR.

Results: Rescaled BTP shared the same reference interval with rescaled Scr and ScysC and showed acceptable diagnostic performance (S = 73.1%, Sp = 86.5%), comparable to Scr (S = 71.0%, Sp = 90.5%) and ScysC (S = 80.7%, Sp = 92.9%). Rescaled BTP can be used in the FAS-equation with comparable performance as Scr and ScysC, but the Scr/ScysC/BTP-combined FAS-eq. (P10 = 57.8%, P30 = 96.6%) did not outperform the Scr/ScysC-combined FAS-eq. (P10 = 57.1%, P30 = 96.3%).

Conclusions: Rescaled BTP is a valid alternative to Scr or ScysC to diagnose kidney function. The FAS-concept can be applied to BTP or the combination of BTP, Scr and ScysC.