Combined Group I and III ABO Discrepancies in Multiple Myeloma with IgG-Lambda Type: A Case Report.

<bold>Objective: </bold>To report a case with unusual ABO discrepancies caused by coexistence of the loss of anti-B isoagglutinin and rouleau formation.<bold>Clinical Presentation and Intervention: </bold>A 79-year-old female diagnosed as having multiple myeloma (MM) with monoclonal IgG-λ type showed rouleau formation in peripheral blood smear. The ABO and Rh blood type before the diagnosis of MM was A+, but the following ABO grouping was interpreted as AB+. The ABO genotype revealed the subtypes A102 and O101, which confirmed her ABO phenotype as A+.<bold>Conclusion: </bold>This was a case of combined group I and III ABO discrepancies mimicking blood group AB. [ABSTRACT FROM AUTHOR]