Renal response to a protein load persists during long-term follow-up of children after renal transplantation.

Abstract

Kidney donors and transplant recipients may be at risk of complications from glomerular hyperfiltration of the single kidney. It has been assumed that tests of the existence of renal functional reserve [delta glomerular filtration rate (deltaGFR), delta effective renal plasma flow (deltaERPF)] can be used to demonstrate hyperfiltration. It would therefore be of interest to evaluate the response of the kidney graft to a protein load. i.e., testing the renal reserve and to find out whether a reduction in baseline GFR is preceded by a loss of deltaGFR. We repeatedly studied the change in GFR and renal plasma flow (ERPF) after an oral protein load in 30 children after renal transplantation (Tx). Follow-up time was 1.0-8.0 years. Renal function was evaluated with the clearances of inulin and para-aminohippuric acid (PAH). Seven recipient/donor pairs were examined twice (median 0.3 and 4 years, after Tx). The baseline GFR and ERPF remained stable throughout the follow-up and the increase after stimulation (deltaGFR and deltaERPF) did not change in the whole group of Tx children over the years. However, a reduction in the baseline GFR from the first to the last investigation occurred in 23 of 30 children. In the 23 patients whose baseline GFR decreased, deltaGFR was still preserved. In the recipient/donor pairs, the baseline GFR and ERPF were the same, but on the second investigation, donors showed higher deltaGFR. Despite fairly low baseline GFR and ERPF values in the Tx children, no change occurs in the capacity to increase GFR and ERPF after a protein load during follow-up, which suggests that they are not maximally hyperfiltrating.