Glomerular filtration rate in children following renal transplantation

Most studies evaluating renal function post-renal transplantation in children have used serum creatinine (S_Cr) or estimates of its clearance (C_SCH). When renal function is impaired both S_Cr and the C_SCH overestimate glomerular filtration rate (GFR), especially during cyclosporine therapy. This study measured GFR in 64 children (age range: 4-19 years) with stable renal function who received renal allografts at the Childrens Medical Center of Dallas, 31 from live related donors (LRD) and 33 from cadaveric donors (CAD). ¹²⁵I- iothalamate clearance (C_IO) was used as the reference standard for measuring GFR. Data from 100 C_IO studies, were analyzed and results reported as mean ± S.E.M. C_IO performed during the first year after renal transplantation in 23 children who received allografts from LRD was 72.4±5.5 ml/min per 1.73 m² compared to 50.4±7.4 ml/min per 1.73m² in 18 children who received allografts from CAD (p<0.05). Beyond the first year post-renal transplantation there was no difference in C_IO between LRD and CAD allografts. When S_Cr was compared to C_IO, the relationship was nonlinear. C_IO was also compared to the simultaneous estimation of creatinine clearance by C_SCH. The overestimation of GFR by C_SCH was inversely proportional to the level of renal function. When renal function was normal or mildly reduced (C_IO>50 ml/min per 1.73 m²), C_SCH closely approximated C_IO. When renal function was moderately to severely curtailed (C_IO < 50 ml/min per 1.73 m²), C_SCH overestimated C_IO by 43.6±5.6%. The study concludes that in children with renal transplant: 1) C_IO is higher in allografts from LRD compared to CAD kidneys only in the first 12 months following renal transplantation; 2) S_Cr is a poor predictor of C_IO; and 3) C_SCH consistently overestimates GFR children following renal transplantation unless renal function is normal or only mildly decreased.