A pregnant woman at 20 weeks gestation with chronic hypertension is maintained on methyldopa. She remains asymptomatic, but routine labs show a positive direct Coombs test without significant anemia. This finding reflects:
- A Autoimmune hemolytic anemia requiring immediate transfusion
- B Feto-maternal hemorrhage
- C Drug-induced autoantibody formation against red cell antigens, often serological alone ✓
- D Hereditary spherocytosis unmasked by pregnancy
Correct answer: C. Drug-induced autoantibody formation against red cell antigens, often serological alone
Explanation
Methyldopa induces IgG autoantibodies directed against red cell rhesus antigens in up to 25 percent of patients on long-term therapy. Most develop only a positive direct Coombs test without hemolysis; overt hemolytic anemia occurs rarely and usually reverses on stopping the drug. It remains a first-line antihypertensive in pregnancy because of decades of fetal safety data. A positive Coombs test alone does not mandate transfusion or indicate hereditary spherocytosis.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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