Background: The critical nephron mass needed to meet the metabolic demands of an individual depends on the body-weight. This study evaluated the effect of the kidney transplant ultrasonographic size to recipient body-weight ratio (Tx/W) on the outcome of kidney transplantation.
Methods: A consecutive series of 104 cadaveric renal transplants was studied. Transplant cross-sectional area (TXSA) was measured ultrasonographically in the first week after transplantation as an index of renal size. A 'nephron dose' index (Tx/W) was calculated by dividing TXSA by recipient weight and was used to define three groups of patients, with high (more than 0.45), medium (0.3-0.45) or low (less than 0.3) Tx/W ratios. Isotope glomerular filtration rate (GFR) measurements were made at 1, 6 and 12 months after transplantation.
Results: The serum creatinine level was significantly lower in the first 5 years after transplantation in patients with a high Tx/W ratio than in those with a medium or low ratio. GFR measurements were marginally higher in the groups with a high and medium Tx/W ratio compared with the low Tx/W group. A statistically significant association between Tx/W ratio and graft survival was not found.
Conclusion: The renal transplant size to recipient weight ratio was an important determinant of long-term renal allograft function in this study. Extreme mismatching between allograft and recipient size should be avoided where possible, but the findings presented require confirmation in larger studies before clear recommendations can be made about size matching and kidney allocation.