Development of a beta-trace protein based formula for estimation of glomerular filtration rate

Beta-trace protein (BTP) is a novel marker of glomerular filtration rate (GFR). To date, no pediatric formula for calculating GFR based on BTP has been developed. We measured GFR, serum creatinine and BTP in 387 children who underwent 474 ^99mTc-diethylene triamine pentaacetic acid renal scans. A BTP-based formula for estimating GFR was derived using stepwise linear regression analysis. A separate control group of 116 measurements in 99 children was used to validate the novel formula. A formula was also developed for each gender. The novel formula is: \( {\text{GFR}} = {\text{1}}{0^\wedge }\left({\text{1}}.{\text{9}}0{\text{2}} + \left( {0.{\text{9515 x LOG}}\left( {{\text{1}}/{\text{BTP}}} \right)} \right) \right) \). The Spearman rank correlation coefficient between the BTP-derived GFR estimate and the measured GFR was 0.80 [95% confidence interval (CI) 0.76–0.83], which is substantially better than that derived with the Schwartz formula (r = 0.70, 95% CI 0.65–0.74). The Bland–Altman analysis revealed a mean bias of 1.21% [standard deviation (SD) 28%] in the formula development dataset, which was virtually identical to the 1.03% mean bias (29.5% SD) in the validation group and no different from the Schwartz formula bias. The percentage of values within 10% (33.0 vs. 28.3%) and 30% deviation (76.8 vs. 72.6%) were better for BTP-based formula than for the Schwartz formula. Separate formulas according to gender did not perform better than that for the pediatric population. This BTP-based formula was found to estimate GFR with reasonable precision and provided improved accuracy over the Schwartz GFR formula.