Precise determination of HLA antibodies is essential for patients awaiting transplantation. HLA antigens that are recognized by a patient are listed in UNOS as unacceptable antigens (UA) and donors having those antigens are excluded from offering the patient an organ. The use of solid-phase assays (SPA) for detecting HLA antibody has been extremely important in identifying UA and improving organ allocation. However, in some cases, SPA can give false-positive results and detect antibody that is not reactive in the flow cytometry crossmatch (FCXM).

In our institution, the HLA antibody profile of a patient is determined by means of a single antigen bead (SAB) assay and confirmed with a PRA (phenotype) bead assay from one of the two companies that commercialize tests for this purpose (Vendor #1). These confirmed specificities (MFI≥2000) are uploaded in UNOS as UA. For this study, 4 patients were found to have high reactivity by the SAB assay but were negative by the PRA bead assay (Table 1). All these patients showed strong antibodies to all HLA-DRB1 antigens including self-antigens. In order to unquestionably define the presence or absence of HLA antibodies, 10 surrogate FCXM were performed on a particular patient (#4) with strong HLA class II DSA (MFI≥5000) to all the donors. All of the FCXM were negative despite the presence of high level DSA. The patient HLA antibody profile was then analyzed by Vendor #2's SAB assay. Results from this second assay were completely negative (Table 1).

This study shows that the use of SAB as the sole method for UA determination can lead to a huge disadvantage for patients with false-reactivity. The use of two different bead assays (PRA and SAB) and/or different commercial SAB platforms in the testing algorithm for HLA antibody determination would prevent patients from being inappropriately excluded from receiving an organ due to false-positive SPA results.

CITATION INFORMATION: Jaramillo A, Nelson L, Desmarteau Y, Labuda B, Barrios K, Lunz J, Heilman R, Pando M. Inconsistent HLA Antibody Reactivity Detected with Different Solid-Phase Assays. Am J Transplant. 2016;16 (suppl 3).

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