Technician Mayo Clinic-Rochester Dodge Center, Minnesota
Body: Virtual crossmatch is widely accepted by CLIA, FDA, and other regulatory authorities as a method to assess immune compatibility for transplantation. Its success relies heavily on the accurate identification of HLA antibodies, which is primarily achieved through solid-phase single antigen bead (SAB) assays. However, these assays can be affected by false-positive reactivity patterns, particularly with HLA-C and HLA-DR antigens, as previously reported. Here, we describe a unique case of false-positive pan-HLA-A reactivity.
The patient is a 57-year-old male who underwent a combined liver-kidney transplant one year ago, due to hepatorenal syndrome. Patient presented with a calculated panel reactive antibody (CPRA) of 0% at the time of transplant. He received standard immunosuppression with basiliximab, mycophenolate, methylprednisolone and Tacrolimus. Post-transplant SAB testing at one, and four months continued to show 0% CPRA. The patient remained clinically stable, with normal liver and kidney function tests. However, at one-year post-transplant, SAB testing revealed widespread reactivity against HLA-A antigens, with mean fluorescence intensity (MFI) values ranging from 1,000 to 20,000. Notably, antibodies were detected against both self and donor-specific HLA-A antigens (see figure), despite continued normal allograft function and biopsy results. Further HLA testing was conducted to establish the reality of these antibodies.
Further investigation included: Acid treatment of beads, which eliminated reactivity, suggesting the absence of antibodies targeting denatured antigen forms.
Testing with an alternate vendor’s SAB assay, which yielded negative results.
Use of screening beads, which were also negative.
Surrogate flow cytometric crossmatches with two different cell sources, both of which were negative.
Conclusion: This case represents a rare instance of false-positive pan-HLA-A reactivity in LabScreen SAB assay. Despite high MFI values, no clinical or functional evidence of allograft injury was observed. These findings underscore the need for further studies to evaluate the clinical significance of such patterns and to support the development of improved assays with reduced false-positive rates.
