http://onlinelibrary.wiley.com/doi/10.1111/ajt.13015/fullSelecting Appropriate Controls for Kidney Donors—Reply
P. P. Reese1,2,*, R. D. Bloom1, H. I. Feldman1,2, A. X. Garg3, A. Mussell2, J. Shults2 andJ. H. Silber4,5
DOI: 10.1111/ajt.13015
American Journal of Transplantation
Volume 15, Issue 1, pages 287–288, January 2015
*Corresponding author: Peter P. Reese, peter.reese@uphs.upenn.edu
To the Editor:
It is not possible to randomize an individual to become a living kidney donor. Therefore, we agree with Mjøen and Holdaas that it is necessary to examine the comparability of the baseline characteristics of the donor and nondonor groups in any study of living donor outcomes [1]. We stand by the conclusion of our manuscript, which reads: “In the context of careful medical evaluation and selection, older donors should expect similar medium-term survival and risk of CVD compared to healthy members of the general population” [2], p. 1859.
Mjøen and Holdaas [1] note that our methods included restriction of the comparison group to nondonors who, in serial interviews with the Health and Retirement Study (HRS), denied a range of relevant health conditions such as diabetes and cardiovascular disease. The HRS participants in the comparison group also needed to rate their overall health as “good,” “very good,” or “excellent.” These were the strategies used to create a nondonor group with a low prevalence of serious medical problems that would serve as a useful benchmark when interpreting outcomes among older live kidney donors. However, we did not have serological values, medical records or abdominal imaging to further characterize the health of the nondonors. Mjøen and Holdaas recapitulated this limitation that we acknowledged in the manuscript, namely the potential for residual confounding by unrecognized medical problems in the nondonor group [2].
Mjøen and Holdaas [1] also draw attention to the separation of the donor and nondonor survival curves in our Figure 2. Yet, that separation was not significant (p = 0.21) in the primary analysis (donors ≥55 years). A substantive conclusion about this study's validity should not be based on this small and statistically insignificant difference in survival, which may only reflect sampling noise.
In Table 1, we present a summary of donor comparison groups from recent studies that reported mortality. The table includes an important study by Mjøen et al that also relied in part on data from interviews to generate a healthy comparison group of nondonors [3]. The table examines whether individuals were excluded from the nondonor groups because of medical abnormalities for which live donors are screened [4]. In each case, the approach taken to assemble the nondonor group has limitations. We hope that future studies will generate new knowledge about long-term donor outcomes using comparison groups that, while likely still imperfect, represent improvements over existing work.
Table 1. Nondonor groups used as comparators in recent studies of outcomes after live kidney donation
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