Does graft mass impact on pediatric kidney transplant outcomes?

The aim of this study is to assess the evolution of renal size and function in pediatric transplant patients according to the graft mass/recipient size ratio.

Fifty pediatric renal transplant recipients were followed over 2 years. Grafts were weighed, and three different graft mass/m(2) ratios were determined: (1) low graft mass (58 g/m(2), range 31-57 g/m(2)), (2) median (142 g/m(2), range 59-141 g/m(2)) and high (267 g/m(2), range 143-353 g/m(2)). Patients underwent repeated ultrasound Doppler scans and repeated measurements of estimated glomerular filtration rate (eGFR; 1 week and 1, 6, 12 and 24 months), urinary retinol-binding protein (RBP) and proteinuria (1 week and 6, 12 and 24 months).

The volume of renal tissue increased by 12 ± 5.6 cm(3) at 24 months (p = 0.035) in the low graft mass and decreased by -14 ± 7 cm(3) (p = 0.046) in the high graft mass. The eGFR increased when either low (30 ± 5 ml/min/1.73 m(2), p < 0.001) or median (19 ± 4 ml/min/1.73 m(2), p < 0.001) graft mass was transplanted but remained stable when high graft mass was transplanted. The resistive index (RI) presented a significant decrease throughout early follow-up in the transplants involving low and median graft mass, whereas a slight rise was observed in those involving high graft mass. A significant difference was apparent 6 months post-transplant. Transplants of low and median graft mass were associated with an initial higher urinary RBP. No significant differences in proteinuria were detected.

Small kidneys undergo increases in volume and function without escalation of either proteinuria or urinary RBP, characterizing an adequate adaptation to the recipient. Children receiving larger kidneys present a reduction in volume, stable GFR and higher RI at 6 months.