ABO blood typing with tissue samples: adsorption-elution on finely sliced fingernail fragments, and the efficacy of blocking nonspecific reactions with skim milk in saline.

Serologic blood typing can be a challenge in patients who have been emergently transfused with type O red blood cells, have ABO forward-reverse mismatches, or display chimerism. Typing by adsorption-elution using fingernail specimens is an alternative, but nonspecific binding of monoclonal anti-A/anti-B antibodies can occur. To block nonspecific binding, we used a saline solution with 10% skim milk on finely sliced fingernail fragments that had been degreased with anhydrous ethanol. Three commercially available anti-A/anti-B reagent kits worked well with this method. Substituting anhydrous ethanol for previously reported ether-ethanol mixtures allowed all steps to be performed safely in an open laboratory. Thus, a patient's true blood type can be identified despite ABO subtype discrepancies or after type O RBCs are administered without pre-transfusion testing.