Ten days after uncomplicated elective surgery requiring transfusion of two units of packed red cells, a 45-year-old man develops fever, jaundice, dark urine and a haemoglobin fall from 10.5 to 7.2 g/dL. Direct antiglobulin test is positive. The antibody specificity most classically responsible for this delayed pattern, through a brisk anamnestic response after previous sensitisation, is:
- A ABO isoagglutinins
- B Kidd (JK) system antibodies ✓
- C Lewis system antibodies
- D Anti-D
Explanation
Kidd antibodies are notorious for falling below detectable levels between exposures, then mounting a rapid anamnestic response 5 to 10 days after rechallenge, causing extravascular delayed haemolysis with falling haemoglobin, jaundice and positive direct antiglobulin test. ABO antibodies are naturally occurring IgM and cause immediate intravascular haemolysis within minutes. Lewis antibodies are cold-reacting, usually IgM and rarely cause clinical haemolysis, while anti-D typically arises in D-negative individuals after explicit Rh-incompatible exposure such as pregnancy.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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