The Impact of Age and Body Composition on the Agreement between Estimated and Measured GFR in Heart Transplant Recipients.

Background: Estimated GFR (eGFR) has shown poor agreement with measured GFR (mGFR) in several populations. We investigated the impact of age and body composition on the accuracy and precision of eGFR in heart transplant (HTx) recipients.

Methods: In a longitudinal, observational, retrospective study design, patients receiving first-time HTx with at least one registered mGFR value within 15 months after HTx and a corresponding plasma creatinine were included. GFR was measured by 51Cr-EDTA and eGFR calculated by creatinine-based CKD-EPI formula.

Results: A total of 150 patients with a total of 723 mGFR measurements were included. During the first year after HTx, mean weight increased by 4.2 kg (CI: 3.2 to 5.1) followed by an annual decrease of 0.35 kg/year (Cl: -0.05 to 0.74). mGFR increased by 7.5 mL/min (Cl: 3.2 to 11.8) the first year but was stable hereafter (0.0 mL/min/year; CI: -1.0 to 1.0). The initial weigh gain and increase in mGFR were most pronounced in patients <45 years. Neither eGFR adjusted nor unadjusted for BSA detected the initial increase in mGFR. At 1 year after HTx, limits of agreement on the Bland-Altman plot were -37.2 to 33.1 mL/min with a bias of -2.1 mL/min (Cl: -5.0 to 0.9). In patients <45 years, eGFR significantly overestimated mGFR by 7.1 mL/min (Cl: 1.0 to 13.2) and showed a significant lower precision than patients >45 years. There was no effect of BMI class, weight, BSA, or change in BMI class on the difference between eGFR and mGFR.

Conclusion: eGFR is, on average, accurate but imprecise in HTx patients. The agreement is affected by age but not body composition.