Which of the following is a Kidd blood group antigen commonly tested in serology?

• A. Jk^a
• B. Jk^b
• C. In(Jk)
• D. Fy^a

Answer: (A)

Kidd blood group testing centers on two main antigens, Jk^a and Jk^b. Jk^a is the form most commonly encountered and typed in routine serology because it is highly relevant clinically; antibodies against Jk^a are frequently encountered and can cause transfusion complications, so labs often screen for or type this antigen to prevent reactions. The Kidd system also includes Jk^b, but it is not as widely emphasized in standard serology panels as Jk^a. For contrast, In(Jk) is not part of the Kidd system, and Fy^a is a Duffy antigen, not Kidd. Thus, Jk^a is the Kidd antigen most commonly tested in serology.