Effect of decalcification on the immunohistochemical expression of ABH blood group isoantigens

Immunohistochemical stains for ABH blood group antigens were recently shown to be useful ancillary tools for sorting out specimen mix-ups in surgical pathology, irrespective of the fixatives used. However, the effects of decalcification on the expression of these antigens are not known. Therefore, to examine the validity of using ABH blood group immunohistochemistry in decalcified tissues, we studied the immunohistochemical expression of ABH blood group antigens in B5-fixed, decalcified, paraffin-embedded archival bone marrow specimens from 43 consecutive patients (13 blood group A, 6 group B, 20 group 0, and 4 group AB). Immunohistochemical staining for A, B, and H blood group antigens was performed with monoclonal antibodies and an avidin-biotin detection method with citrate antigen retrieval. The results of immunohistochemistry were correlated with patients' blood groups as determined by serology. Immunohistochemical expression of the A and B blood group antigens with good staining intensity was detected in erythrocytes and endothelial cells. The immunoreactivity for H blood group antigen was attenuated by the decalcification process and could not be enhanced with citrate antigen retrieval. However, in all 43 cases, the A and B antigen staining pattern was concordant with patients' blood groups as determined with serology. These results show that decalcification does not have adverse effects on immunohistochemical expression of the A and B blood group antigens in tissue sections but may nullify the expression of H isoantigen. However, based on A and B immunoreactivity patterns, immunostaining for ABH blood group antigens can be helpful in resolving problems of specimen mix-ups and tissue floaters in decalcified specimens.