Rouleaux mimicking anti-H in molecularly confirmed para-Bombay siblings: a diagnostic pitfall.
Bodanapu Vinay, Arun Rajendran, U B Davood et al.
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Case in brief
Two siblings from India were found to have a para-Bombay phenotype during evaluation of blood-group serology. In the index case, red cells did not react with anti-H lectin, while weak reactivity with pooled group O red cells during reverse grouping and thermal amplitude testing raised concern for clinically significant anti-H. Microscopy, saline replacement, adsorption-elution studies, and saliva inhibition testing instead supported rouleaux-induced pseudoagglutination. Molecular testing identified homozygous FUT1 c.328G>A and FUT2 c.357C>T mutations in both siblings, consistent with para-Bombay secretor phenotype and enabling appropriate transfusion planning.
What made this case unusual
Rouleaux-induced pseudoagglutination mimicked anti-H reactivity, creating a serologic diagnostic pitfall in molecularly confirmed para-Bombay siblings.
Diagnostic / clinical pearl
When weak reactivity suggests anti-H in a suspected para-Bombay phenotype, distinguish true antibody-mediated agglutination from rouleaux using detailed serologic evaluation and, where available, molecular characterization.
Why it matters
Correctly identifying pseudoagglutination can support appropriate transfusion planning and avoid unnecessary restrictions on compatible blood components.