The calculated Panel Reactive Antibody (cPRA) is an estimate for the probability of positive virtual CrossMatch, considering HLA typing of a given group of potential donors, based on the HLA antigens from which a transplant candidate is sensitized [1 ,2].

For this cPRA estimator we used HLA (allelic and haplotype) frequencies of 37,993 bone marrow voluntary donors, published previously [3]. cPRA values calculation was done as described by Kransdorf et al in 2017 [4]. Briefly, from the selected antigens, cPRA is calculated considering those pre-defined allelic and haplotypic frequencies, being:

for allelic frequencies (AF): S1 = AF(HLA-A*) + AF(HLA-B*) + AF(HLAC*) + AF(HLA-DRB1*);

for haplotypic frequencies (HF): S2 = HF(HLA-A*-B*) + HF(HLA-A*-C*) + HF(HLA-A*-DRB1*) + HF(HLA-B*-C*) + HF(HLA-B*-DRB1*) + HF(HLA-C*-DRB1*);

S3 = HF(HLA-A*-B*-C*) + HF(HLA-A*-B*-DRB1*) + HF(HLA-A*-C*-DRB1*) + HF(HLA-B*-C*-DRB1*);

S4 = HF(HLA-A*-B*-C*-DRB1*).

According to the Hardy-Weinberg equilibrium: cPRA = 1 - (1 - S1 + S2 - S3 + S4)^2.

Transplantability percentages (T%), given herein, return the percentages of possible donors that are AB0 identical or AB0 compatible and have HLA antigens acceptable to the potential candidate. For T% calculation we used blood groups' allelic frequencies previously described for Portuguese blood donors [5]. The respective AB0 groups genotype frequencies were estimated applying Hardy-Weinberg principles.

In comparison to cPRA value, T% has the advantage of considering both the HLA and AB0 systems to estimate the possibility of finding a compatible donor for a particular transplant candidate.

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[1] - Bruno A Lima, Helena Alves. Seleção do Par Dador-Recetor em Transplante Renal:Resultados Comparativos de uma Simulação. Acta Med Port 30(12), 2017: 854-860

[2] - Bruno A. Lima, Miguel Mendes, Helena Alves. Hypersensitized candidates to kidney transplantation in Portugal. Port J Nephrol Hypert. 27(2), 2013: 77-81

[3] - Bruno A. Lima, Helena Alves. HLA-A, -C, -B, and -DRB1 allelic and haplotypic diversity in bone marrow volunteer donors from Northern Portugal. Organs, Tissues & Cells. Volume 16(1), 2013, March: 19-26

[4] - Kransdorf E, Pando M, Gragert L, Kaplan B. HLA Population Genetics in Solid Organ Transplantation. Transplantation 101(9), 2017: 1971-1976

[5] - Duran J, Chabert T, Rodrigues F, Pestana D. Distribuição dos grupos sanguíneos na população portuguesa. AB0 29, 2007: 5-17.