Test results showed Anti-D 4+ with Rh control 0. What is the most appropriate interpretation?

• A. The patient is Rh negative
• B. The test is inconclusive
• C. The patient has anti-D alloantibody
• D. The patient is Rh positive

Answer: (D)

Rh typing using anti-D reagent on the patient’s red cells is being described. A strong 4+ reaction indicates the D antigen is present on the patient’s red cells. The Rh control being 0 means there is no non-specific agglutination, so the observed agglutination is specifically due to the D antigen. Taken together, this shows the patient is Rh positive (D positive).

If the patient were Rh negative, anti-D would not cause agglutination of their own red cells. A test inconclusive result would typically show a problematic or mixed pattern, and finding an anti-D alloantibody would refer to antibodies present in the patient’s serum reacting with D-positive cells, which is a different testing context (antibody screen rather than forward typing).