The poor accuracy of indirect measurements of cadaveric donor kidney weights.

Reports that examined the issue of whether transplantation of inadequate nephron mass may be a risk factor for long-term allograft failure yielded conflicting results. One of the more accurate methods of estimating glomerular mass is kidney weight. Most of the clinical studies used body surface area (BSA) or kidney length as estimates of kidney weight. To test the hypothesis that indirect measures of kidney weight are accurate estimates of kidney weight, we compared the kidney weight of 41 consecutive cadaveric kidneys to donor BSA, dimensions measured with calipers at the time of transplantation, and dimensions supplied by the Organ Procurement Agency (OPA). Linear regression analysis was used with kidney weight as the dependent variable and BSA, kidney length, or kidney volume as the independent variable. Kidney length measured with calipers was also compared to kidney length supplied by the OPA. Kidney weight had the best correlation with kidney volume and kidney length determined by caliper measurements (r = 0.640 and 0.646, respectively). The regression analysis showed that the correlation of kidney weight with BSA was 0.487. The correlation of OPA-provided kidney length with kidney weights was poor (r = 0.410). The linear regression of caliper-measured kidney length versus OPA length yielded a slope of 0.360, instead of an ideal slope of 1. The assumption has been made that kidney weight or a surrogate of kidney weight has an excellent correlation with nephron mass. Some of the variability in studies that attempted to examine the effect of transplanted nephron mass on allograft outcome may be due to inaccurate estimates used for kidney weight. Our data suggest that surrogate measurements of kidney weight may not be accurate. We recommend that measured kidney weight should be used in studies examining the effect of donor renal mass on allograft outcomes.