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A three and a half-year-old girl of Indian ethnic origin presented with a 2-day history of fever and sore throat. She had also been passing red urine for the previous 24 hours. Her blood count showed: white cell count 27.5 x 109/l, red cell count 2.76 x 1012/l, hemoglobin concentration 81 g/l, hematocrit 0.22 l/l, mean cell volume 80 fl, mean cell hemoglobin 29.6 pg, mean cell hemoglobin concentration (MCHC) 370 g/l. The increased MCHC suggested the presence of spherocytes, irregularly contracted cells or some other hyper-dense cells. A blood film confirmed the presence of numerous spherocytes and in addition was leucoerythroblastic and showed red cell agglutination and erythrophagocytosis by neutrophils (Figures). Other neutrophils had large vacuoles, similar in size to an erythrocyte, containing amorphous debris. There were also atypical lymphocytes, which appeared reactive. Lactate dehydrogenase and bilirubin were increased. The reticulocyte count was initially normal (46 x 109/l) but subsequently rose. The combination of marked spherocytosis, red cell agglutinates and erythrophagocytosis was considered strongly suggestive of paroxysmal cold haemoglobinuria (PCH) and confirmatory tests were performed. A direct antiglobulin test was positive for complement (+++) and negative for immunoglobulin (Ig) G. A Donath –Landsteiner test was positive. Red cell transfusion was required and full recovery had occurred by 3 weeks.

Although the Donath-Landsteiner antibody is an IgG antibody it is usual for the direct antiglobulin test in PCH to show complement only since the antibody that binds to the cell and fixes complement in the cold detaches from the red cell membrane on warming. Confirmation of the diagnosis is by demonstration of the presence of an anti-P antibody and biphasic haemolysis. However the blood film appearances are highly characteristic and permit a rapid presumptive diagnosis.