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A middle aged female with refractory autoimmune thrombocytopenia, post-splenectomy, was prescribed azathioprine as an immunosuppressive agent. She then developed anemia and macrocytosis. Her thrombocytopenia persisted. Her blood count showed: white cell count 8.1 x 109/l, hemoglobin concentration 95 g/l, mean cell volume 109 fl and platelet count 23 x 109/l.

Her blood film showed macrocytosis, oval macrocytes, elliptocytes and occasional erythroblasts and myelocytes. However, the most striking feature was the presence of numerous Howell-Jolly bodies (images). This is a feature of megaloblastic hemopoiesis in a hyposplenic patient. In this patient the megaloblastosis was the result of azathioprine therapy. Similar blood films can be seen when patients with celiac disease with splenic atrophy develop folic acid or vitamin B12 deficiency. In the past these morphological features were also sometimes observed when a total gastrectomy and splenectomy were performed in a patient with carcinoma of the stomach with no replacement vitamin B12 therapy being given. The formation of numerous Howell-Jolly bodies occurs as a dyserythropoietic feature observed in megaloblastic anemia. In the absence of a spleen, these red cell inclusions are not removed and they become very prominent in the blood film.