The present paper reports a case of α-methyldopa (Aldomet) induced Coombs positive hemolytic anemia in Japanese and discusses some clinical and etiological points.
A 57-year-old woman had been administered “Aldomet” 500 mg/day for two years developed anemia and laboratory examinations revealed Hb 9.6g/100 ml, RBC 2.59×106, Ht 24.5%, reticulocyte 9.5%, serum bilirubin 1.7mg/100 ml, and S-LDH 453u. Both direct and indirect Coombs tests (D.C.T. and I.C.T.) were positive, showing positive with anti-IgG and anti-κ, but negative with anti-λ. Spherocytosis was observed and red cell osmotic fragility increased. The red cell ATP level was low, and Na+, K+ATPase activity higher normal. Glucose-6-phosphate dehydrogenase activity was increased. A bone marrow examination showed erythroid hyperplasia (M:E=1:1). “Aldomet” was discontinued and anemia and reticulocytosis improved gradually. Although both D.C.T. and I.C.T. remain positive (six months later), the titers decreased significantly.
We found another Coombs positive case among fourteen hypertensive Japanese on “Aldomet”.
The red cell membrane enzyme, Na+, K+ATPase, was measured and the kinetics showed Km for K+ (potassium) of 2.7 mM (normal 2.6-3.5 mM). But Na+, K+ATPase and total ATPase, which were plotted as a function to ATP concentration, showed a peak at 0.3 mM ATP concentration and hence Lineweaver-Burks plot was not linear. This peak disappeared after the antibody elution technique.
This finding suggests that some population of red cell ATPase, especially Na+, K+ATPase, has gotten an altered affinity to ATP by way of antibody attachment to the cell membrane.
