Beta‐Trace Protein‐Based Equations for Calculation of GFR in Renal Transplant Recipients

Recently, we showed that serum beta‐trace protein (BTP) is an alternative marker of glomerular filtration rate (GFR) in renal transplant recipients (RTR). We have now developed three BTP‐based GFR formulae derived by multiple regression analyses from the patients who had participated in that study. Currently, we validated the diagnostic performance of these BTP‐formulae in 102 consecutive RTR who underwent a technetium diethylenetriamine pentaacetic acid (DTPA) clearance for GFR measurement in comparison to the re‐expressed Modification of Diet in Renal Disease (MDRD) equation and a recently proposed BTP‐based equation (referred to as ‘White equation’). The best‐performing BTP formula was found to be: GFR = 89.85 × BTP−0.5541× urea−0.3018. This equation estimated true GFR virtually without bias (+0.43 mL/min/1.73 m 2 , not significant [NS]), while a small, but significant, overestimation was seen for the MDRD formula (+3.43 mL/min/1.73 m 2 , p = 0.003). Precision and accuracies within 50% of true GFR (93.1% and 88.2%, respectively) tended to be higher for the BTP formula, but the differences did not reach significance. The White equation overestimated the true GFR by 9.43 mL/min/1.73 m 2 (p = 0.001), and was inferior with respect to precision and 50% accuracy (79.4%). BTP‐based GFR calculations are reliable, and may serve as an alternative to the re‐expressed MDRD equation. A serum beta‐trace protein‐based formula for glomerular filtration rate is described that estimates true GFR virtually without bias, and may serve as an alternative to calculations such as the MDRD equation.