An anaemic fetus shows hydrops despite maternal anti-D being the identified antibody. After delivery, the direct antiglobulin test on the baby is negative and repeat maternal antibody screening identifies a new antibody. Which red cell antigen is most often responsible for such severe haemolytic disease with weakly reactive or negative DAT?

• A Kell (K1) ✓
• B c antigen
• C E antigen
• D Duffy (Fya)

Explanation

Anti-Kell is the most common clinically significant non-D antibody causing severe haemolytic disease of the fetus and newborn. Unlike anti-D, Kell antibodies suppress erythroid precursors directly, so anaemia is out of proportion to haemolysis, reticulocytosis is minimal, and the direct antiglobulin test may be weakly positive or negative despite profound fetal anaemia. Anti-c and anti-E also cause HDFN but through classic extravascular haemolysis with strongly positive DAT. Duffy antibodies rarely cross into severe fetal disease because Fya expression on fetal cells is limited.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.