Temporal changes in the composition of a large multicenter kidney exchange clearinghouse: Do the hard‐to‐match accumulate?

One criticism of kidney paired donation (KPD) is that easy‐to‐match candidates leave the registry quickly, thus concentrating the pool with hard‐to‐match sensitized and blood type O candidates. We studied candidate/donor pairs who registered with the National Kidney Registry (NKR), the largest US KPD clearinghouse, from January 2012‐June 2016. There were no changes in age, gender, BMI, race, ABO blood type, or panel‐reactive antibody (PRA) of newly registering candidates over time, with consistent registration of hard‐to‐match candidates (59% type O and 38% PRA ≥97%). However, there was no accumulation of type O candidates over time, presumably due to increasing numbers of nondirected type O donors. Although there was an initial accumulation of candidates with PRA ≥97% (from 33% of the pool in 2012% to 43% in 2014, P = .03), the proportion decreased to 17% by June 2016 (P