Age, exclusion criteria, and generalizability of randomized trials enrolling kidney transplant recipients

The proportion of elderly (≥65 years) kidney transplant recipients (KTRs) doubled in the United States from 1999 to 2008. Given higher mortality, more medication side effects, and less rejection among elderly KTRs, optimal care of these patients may require tailored decisions about transplant therapeutics. It is unknown whether participants in transplant clinical trials-which generate the best evidence for patient care-are representative of the aging population of KTRs.

Using PubMed, we identified randomized trials involving KTRs from 1999 to 2008 and determined age-exclusion criteria and the mean age of participants. The mean age of these trial participants was compared with the mean age of the overall population of incident KTRs in the United States.

The 87,222 participants in 573 trials were significantly younger than the US KTR population (P<0.05). This age discrepancy worsened over the study period (during the years 2006 to 2008, the mean age was 45 years for trial participants versus 50 years for US KTRs, P<0.05). Thirty percent of trials had an exclusion criterion based on older age, and 16% excluded recipients aged 65 years or older. In multivariable regression, immunosuppression trials (P<0.01) and trials in higher impact journals (P=0.03) were more likely to exclude the elderly, but there was no significant difference in exclusion of elderly patients based on a trial's geographic location.

Trial participants are younger than KTRs in the United States and many trials exclude older patients. Transplant investigators should make strong efforts to recruit patients across the total age spectrum.