Summary. Bartonella henselae is a hitherto unidentified cause of autoimmune haemolytic anaemia. Here we report a case of Coombs-negative autoimmune haemolytic anaemia. The episode was preceded by exposure to a cat and a non-specific infectious syndrome. Concomitant serum titres of B. henselae antibodies were indicative of a recent infection. The case report suggests that B. henselae infection can trigger secondary autoimmune haemolytic anaemia.Keywords: autoimmune haemolytic anaemia, Bartonella henselae.A 60-year-old-man with a history of smoking, recurring gastric ulcers and arteriosclerotic disease, was referred from another hospital because of severe Coombs-negative haemolytic anaemia. He experienced pleuritic right-sided chest pain for 2 weeks, and night sweats for several weeks. A computerized tomography (CT) scan performed at the referring hospital had revealed a limited pleural effusion at the base of the right lung. In the referring hospital he had been administered amoxicillin/clavulanic acid and doxycyclin for 5 d, but otherwise no new drugs had been added to his prescriptions in the preceding weeks.On arrival the patient was pale and tachypneic, with an otherwise unremarkable physical examination. A blood smear revealed spherocytosis and polychromatophilia, but no schistocytes. Absolute and relative reticulocyte count were strongly elevated, with undetectable serum haptoglobin, unconjugated hyperbilirubinaemia, increased serum lactate dehydrogenase (LDH) ( Table I) and free plasma haemoglobin [390 mg/l on d 3 (normal value 0±100 mg/ l)]. Direct and indirect antiglobulin tests were negative, as were cold agglutinins and Donath±Landsteiner antibodies. Examination of a bone marrow aspirate showed a hyperplastic erythropoiesis, without erythrocyte inclusions or haemophagocytosis.Based on a negative medical and negative family history and on exclusion of other known mechanisms that can produce infection-related anaemia or haemolysis, a diagnosis of Coombs-negative autoimmune haemolytic anaemia was made. Antibiotics were discontinued upon admission (d 1), and methylprednisolone was given at 1 g/d for 3d, followed by oral methylprednisolone in tapering doses. Two units of erythrocyte concentrates were given on d 5. In the following weeks control of haemolytic anaemia was rapidly achieved (Table I).Because of recent exposure to a cat at his daughter's home, serology for B. henselae was requested. On d 8 an IgM titre of 1/64 and an Ig G titre of . 1/512 were found. Follow-up on d 68 gave a negative IgM titre and an IgG titre of . 1/512. Serological tests were otherwise negative for Chlamydia, Mycoplasma pneumoniae, cytomegalovirus, Epstein-Barr virus, parvo virus B19, human immunodeficiency virus (HIV), and hepatitis B and C virus. A CT scan during hospital admission failed to show enlarged lymph nodes or hepatosplenomegaly. DISCUSSIONGiven the patient's recent exposure to a cat, the high antibody titres (both IgG and IgM) specific for B. henselae at the time of the haemolytic episode with negative IgM titres ...