[Cold agglutinin syndrome associated with infectious mononucleosis: A case report].

Background: Cold agglutinin syndrome (CAS) is a hemolytic anemia mediated by antibodies, mainly IgM, whose maximum activity occurs at 4 °C. It happens secondary to infectious, autoimmune or neoplastic diseases, due to the formation of antibodies that cross-react against erythrocyte antigens, particularly of the I system. Here, we describe a case of CAS associated to Epstein-Barr virus (EBV) reactivation in a patient with primary human immunodeficiency virus (HIV) infection. Clinical case: 22-year old man with no medical history, hospitalized due to mononucleosis and anemic syndrome. Hemoglobin of 3.7 g/dL and elevation of lactate dehydrogenase were documented. In the peripheral blood smear it was observed spherocytosis, polychromasia and nucleated erythrocytes. EBV infection was confirmed with serology and viral load, as well as seronegative HIV infection with positive viral load. The C3d monospecific direct antiglobulin test was positive and an irregular antibody screening revealed the presence of an anti-I antibody. The patient received transfusion support and conservative treatment, with remission of the symptoms 2 weeks after admission. Conclusions: Cold agglutinin syndrome is a rare, potentially fatal complication of infectious mononucleosis, which should be considered in the face of findings suggestive of hemolysis in order to initiate support measures in a timely manner.