Given a scenario where a patient's serum agglutinates with group A antigens but not with group B, what blood type does the patient have?

The situation described indicates that the patient's serum reacts with group A antigens but does not react with group B antigens. This reaction pattern suggests that the patient has antibodies against type B antigens, which leads to the conclusion that they cannot have blood type B or AB, as those types would have B antigens present.

Since the serum agglutinates with A antigens, this means the patient has A antigens on their red blood cells. Therefore, the patient's blood type must be A, as they would produce anti-B antibodies in response to the presence of B antigens, which explains the lack of agglutination with those antigens. Thus, the accurate determination of this patient's blood type is A.