If a patient's red cells forward as group O but serum agglutinates B cells (4+), what should be your next step?

When a patient's red blood cells forward as group O but their serum agglutinates B cells with a strong reaction (4+), it suggests that the patient has anti-B antibodies in their serum despite being typed as group O. The next step involves confirming the presence of A antigens, particularly A1 antigens, since individuals who are group O can occasionally carry anti-A or anti-B antibodies, potentially due to subgroups or weak expression of these antigens.

Incubating washed red cells with anti-A1 and anti-A,B is a logical next step because this will help determine whether the patient expresses any A antigen at all, specifically the A1 antigen, which is important for further classification. If the patient has anti-A1, this could explain why their serum agglutinates B cells, as they might be producing antibodies to B cells that express A antigens similar to their A1 antigen. Testing with Dolichos biflorus would specifically identify the presence of A1 phenotype cells, as this lectin agglutinates only A1 type red cells, confirming the specificity of the patient's serum components.

This approach allows for a more nuanced understanding of the patient's blood type and confirming their antibody profile before making any additional decisions regarding blood