The goal of this study was to replicate earlier findings that HLA matching and SES are the overriding factors responsible for the poor results of cadaver donor kidney transplantation among blacks and to investigate other factors influencing outcome.

Data used in these analyses included patients who underwent kidney transplants reported to the United Network for Organ Sharing Scientific Renal Transplant Registry in thirty centers in the United States from October 1987 through December 1991. Data from the UCLA International Transplant Registry were also used to compare U.S. and Canadian centers.

The one-year survival was 80.6% for whites and 76.3% for blacks; the three-year survival was 70.2% for whites and 56.8% for blacks. The one- and three-year survival rates for Hispanics (82.8% and 68.9%) were comparable to those for whites.

Age and sex stratification altered the findings slightly. Among men, there were statistically significant differences in one-year survival only in the 16-30 year age group; and, among women, there were no statistically significant age-adjusted race differences in one-year survival. Racial differences among men in three-year survival existed for patients in the three age groups between 16 and 60 years of ages. The largest difference was in the 16-30 year group because blacks in this group had a large drop in survival compared with the other groups. Among women, statistically significant differences in three-year survival were limited to the 31-45 year age group. “Strong immune responsiveness has also been suggested as a cause of poorer outcome among black patients. Consistent with this idea was our finding that young black recipients had lower 3-year graft survival than older recipients.”

Results of black-white comparisons using projected half-lives paralleled those for one- and three- year survival rates, and were often more striking.

Graft survival, even up to 3 years, was similar between blacks and white transplanted in Canada. In the US, the rate at which dialysis was required varied widely among centers; however, blacks consistently had poorer early graft function than whites.

More blacks had poor early graft function than whites – 34% of blacks required dialysis during the first week, compared with 22% of whites. “Factors such as compliance, SES, education, or type of insurance are unlikely to influence these early measures of graft function.” However, since blacks with no dialysis requirement in the first week still had more rapid graft loss after the first year than whites, the higher rate of early graft dysfunction did not account for poorer long-term outcome in blacks. Additionally, for blacks, quadruple therapy (CsA, AZA, predisone, and antilymphocite globulin or OKT3) resulted in better one-year survival (by 2%) and a greater half-live (5.6 years) than triple therapy (without antilymphocite globulin or OKT3), but rapid graft loss was still seen in patients with quadruple therapy and black-white differences still remained. (In whites, there was no statistically significant difference in one-year and 3-year graft survival rates for triple-drug versus quadruple-drug therapy.)

Difficulties in HLA typing might explain lower graft survival rates in black recipients who tend to have less well-defined HLA antigens. In this study, blacks received kidneys that were significantly more poorly matched for HLA-A, -B, -DR antigens than whites. The best graft survival rates were observed in white recipients who receive the most HLA-A, -B or HLA-DR-matched graft. However, even stratifying for HLA antigen mismatches, one-year survival rates of black recipients were lower by 2-9% than those of whites.

With regard to living related donor transplants, the projected half-lives were also less than half those for whites. Black patients who received HLA-identical sibling donor transplants had much higher half-lives (15.1 years) than other blacks by donor group (4.7 to 6.4 years), however this was still roughly half the half-live for whites receiving HLA-identical sibling donor transplants (28.7 years). The authors argue that, while the good results obtained with HLA-identical sibling transplant might support the contention (that difficulties in HLA type might explain lower survival rates in blacks), the more rapid rate of graft loss after the first year among black recipients of HLA-identical sibling grafts suggests the quality of tissue type does not account for the findings. The authors then suggest that there might be racial differences in the influence of HLA or non-HLA antigen incompatibilities on survival.

The authors conclude that “higher levels of histocompatibility matching can be expected to be useful,” and, “with improved HLA typing of black patients and an increase in black cadaveric donors, a half-life similar to HLA-identical siblings (15 years) can be expected from cadaver donors”.