594 A New Glomerular Filtration Rate Estimation Formula Derived from a Pediatric Heart Transplant Population

Abstract

Purpose: The classic estimation of glomerular filtration rate (GFR) in children overestimates GFR in the transplant population, yet is still used by many centers to determine renal function and design therapeutic interventions. We present a new formula for estimating GFR derived from a population of pediatric heart transplant recipients. Methods and Materials: Isotopic (99Tc DTPA) GFR (iGRF) measurements are performed as part of our routine annual evaluation. We analyzed 1051 iGFR measurements from 244 pts, from 1991 thru 2011 that were done when the pt was at least 2 yo (to eliminate renal maturation effects) and where there was a concomitant creatinine (Cr), height and weight measured. Results: Best fit analysis was performed using height (ht in cm), weight (wt in kg) and Cr (mg/dL) data. The equation which best fit the data (R2 = 0.41) was: (Equation presented) The equation was more accurate in the clinically relevant GFR range of < 100 mL/min/1.73m2. Analysis of goodness of fit for measured GFR's versus standard Schwartz formula yielded R2 = 0.29. Comparison between our estimated GFR (eGFR) from measured GFR, with GFR<100, is illustrated in figure 1. Comparison of the new eGFR estimate from current Schwartz formula eGFR is illustrated in figure 2. (Graph Presented ) Conclusions: Determining renal function is an important aspect of longterm follow-up. Historically, programs have relied on an imprecise estimate of GFR or an expensive, time-intensive measurement of isotopic GFR. We present a new estimate of GFR using actual data from pediatric heart transplant recipients. It more accurately estimates GFR than the Schwartz formula, but with an R2 of 0.41, it may still not be accurate enough to forego formal measurement of iGFR.