Warm autoantibodies mimicking alloantibodies: Three cases of autoantibodies with unusual antigenic specificity

Objectives We describe 3 cases of red blood cell (RBC) autoantibodies with unusual apparent antigenic specificity and discuss the testing methodology and implications of these findings. Methods All immunohematologic testing, including ABO and RhD typing, antibody detection and identification, RBC antigen phenotyping and genotyping, direct antiglobulin tests, and elution studies were performed using standardized and validated methods and reagents. Results Three patients were found to have autoantibodies, which were originally presumed to be alloantibodies. Case 1 was a 60-year-old man with autoanti-Jk(a) following babesiosis; case 2 was a 79-year-old woman with an autoanti-f; and case 3 was a 28-year-old pregnant woman with an autoanti-S. Cases 1 and 2 required RBC transfusions, which were performed with Jk(a)-negative and f-positive RBC units, respectively. No transfusion reactions were reported, and the hemoglobin responded appropriately in both cases. Conclusions These 3 cases complement the minimal literature regarding warm autoantibodies with unusual antigenic specificity and their potential to mediate clinically significant hemolysis. There are only rare reports of warm autoantibodies with specificity for non-Rh antigens, and prior authors have suggested that autoantibodies with mimicking specificity are usually detected only serologically; in contrast, 2 of the 3 patients herein experienced autoimmune hemolytic anemia.

Automated summary

In this study, 3 cases of red blood cell (RBC) autoantibodies with unusual apparent antigenic specificity were described, and the testing methodology and implications of these findings were discussed. All immunohematologic testing was performed using standardized and validated methods and reagents. These 3 cases complement the minimal literature regarding warm autoantibodies with unusual antigenic specificity and their potential to mediate clinically significant hemolysis.