Marked elevation of serum ferritin associated with Anaplasma phagocytophilum infection

Human granulocytic anaplasmosis (HGA) is a tick-borne disease caused by the intracellular bacterial pathogen Anaplasma phagocytophilum. Patients typically present with non-specific symptoms, including high fever, headache, malaise, and myalgias. Laboratory investigations often reveal leukopenia, thrombocytopenia, and an elevation in serum hepatic aminotransferases. A marked elevation in ferritin with or without other features of hemophagocytic/macrophage activation syndrome has been occasionally reported in patients with A. phagocytophilum infection. A case of HGA is described in which the patient had an elevated ferritin of 1964 μg/L. For patients presenting with features of hemophagocytic syndrome including a markedly elevated ferritin, infection with A. phagocytophilum should be considered in the differential diagnosis in the appropriate clinical context (i.e., at-risk geographic location, season, tick exposure) as this distinction has management implications.