In the Duffy blood group system, what is the most common antibody detected?

• A. Anti-Fy^a
• B. Anti-Fy^b
• C. Anti-Jk^a
• D. Anti-I

Answer: (A)

In the Duffy system, antibodies form against specific Fy antigens when a person lacks that antigen and is exposed to it through transfusion or pregnancy. Fy^a and Fy^b are the two main Duffy antigens, and anti-Fy^a is the antibody most commonly detected because Fy^a is a prevalent antigen in many populations and many Fy(a−) individuals will develop anti-Fy^a after exposure. Anti-Fy^b does occur, but it is less common. Antibodies against Jk^a or I belong to other blood group systems, not the Duffy system, so they aren’t the correct focus here.