Which statement about weak D antigens is true?

Which statement about weak D antigens is true?

• A. It is a variant of the D antigen
• B. It is an independent antigen
• C. It is not expressed
• D. It is stronger than D

Answer: (A)

Weak D antigens are a variant form of the D blood group antigen. They occur when some individuals have reduced expression of D epitopes on red cells due to genetic variation in the RHD gene. Because they are still part of the D antigen system, they are not an independent antigen, and the D antigen is simply present at a lower density, which is why reactions with anti-D reagents can be weak. They are not not expressed (they are expressed, just weakly), and they are not stronger than D. This is why describing weak D as a variant of the D antigen is the best way to capture what it really represents.

Weak D antigens are a variant form of the D blood group antigen. They occur when some individuals have reduced expression of D epitopes on red cells due to genetic variation in the RHD gene. Because they are still part of the D antigen system, they are not an independent antigen, and the D antigen is simply present at a lower density, which is why reactions with anti-D reagents can be weak. They are not not expressed (they are expressed, just weakly), and they are not stronger than D. This is why describing weak D as a variant of the D antigen is the best way to capture what it really represents.