The correlation of renal allograft weight to metabolic index ratios and glomerular filtration rate among living-unrelated kidney transplant patients: a cross-sectional study.

OBJECTIVE: This study sought to determine whether there was a relationship between the ratios of renal allograft weight (RAW) and metabolic indices: specifically, recipient body weight (RBW), recipient body mass index (RBMI), and recipient body surface area (RBSA), and posttransplant renal function as measured by glomerular filtration rate (GFR). It also sought to determine which of the 3 ratios, and the minimum ratio, that was predictive of a good GFR as well as to ascertain which computational formula (Cockroft-Gault [C&G] vs abbreviated Modification of Diet in Renal Disease [aMDRD]) better predicts renal function.

METHODS: This cross-sectional study was performed among living unrelated kidney transplant patients who did not manifest rejection, ischemic injury, or postoperative morbidity and mortality from January to December 2006. Donor/recipient matching was based on conventional immunologic parameters. The harvested kidney was weighed after a cold bath and then transplanted by a single surgical team. The 3 ratios, RAW/RBW, RAW/RBMI, and RAW/RBMI were correlated with GFR, which was computed using C&G and aMDRD formulae based on serum creatinine at discharge and at 6 months follow-up. Statistical analysis used STATA 7 and the Pearson correlation using linear regression analysis.

RESULTS: The 53 kidney transplant patients has a mean age of 39.8 years +/- 19 SD (range, 6-74), and slight male predominance (58% vs 42%). RAW/RBW was most positively correlated with GFR estimated by aMDRD (r = .89; P < .001) but negatively correlated with GFR estimated by the C&G formula both at discharge and at 6 months follow-up. A similar trend was observed with RAW/RBMI (r = .79; P < .001), whereas RAW/BSA was related to neither GFR formula. Of the 3 ratios, RAW/RBW best predicted GFR using the aMDRD formula. The minimum RAW/RBW ratio that predicted good GFR (>90 mL/min) at 6 month follow-up was 8.2 (accuracy 88.6%; P = .004).

CONCLUSION: The RAW/RBW and RAW/RBMI correlated with GFR measures by the aMDRD method. Of the 3 ratios, only RAW/RBW was useful to predict GFR, best estimated by the aMDRD formula. A minimum RAW/RBW ratio of 8.2 predicted a good GFR at 6 months posttransplant. The findings suggested that transplanting a small kidney into a heavy patient may be a risk factor for allograft failure and that having a high initial ratio (> or =8.2) of renal allograft weight to initial recipient body weight was an advantage.