Does the OPTN cPRA Calculator Accurately Predict HLA Antigen Frequencies in Pediatric Donors?

Abstract

The calculated panel reactive antibody (cPRA) is an estimate of the likelihood of receiving an HLA-incompatible organ based on an historical sample of solid organ donors of all ages, but has not been validated specifically for pediatric donors. We hypothesized that differences in the ethnic makeup of pediatric and infant vs. adult thoracic organ donors would correspond to differences in HLA antigen frequencies not accurately predicted by the current cPRA calculator. All US thoracic donors for the calendar years 2012-2013 were analyzed for the frequencies of A/B/C and DQ antigen frequencies in pediatric (< 18 years) and infant (< 1year) donors as compared to the overall donor pool and to that predicted by the cPRA calculator. A comparison of the ethnic frequencies for each donor group was also conducted. 10,290 thoracic donors were analyzed, including 1119 < 18 years old and 386 < 1 year old. Caucasians made up 73% of the total cohort, 66% of the pediatric cohort, but only 53% of the infant cohort. (P=0.001) African-Americans and Latinos represented larger percentages of the pediatric and infant donor pools when compared to the total donor pool (p=0.001). Although the cPRA calculator accurately predicted the actual antigen frequency in the total cohort within 4 percentage points, it inaccurately predicted the antigen frequency by as much as 9% for 7/70 (10%) and 9/70 (13%) antigens in the pediatric and infant cohorts, respectively (P = 0.02 and 0.05). Differences were most common for antigens commonly found in African-Americans and Latinos (e.g. A36, B53). The national cPRA calculator underestimates the frequency of certain HLA antigens in the pediatric and infant donor pools and may inaccurately estimate the likelihood of receiving an HLA-incompatible organ in these populations. Differences in antigen frequency are likely the result of minority overrepresentation in the pediatric and infant donor pools.