IgG-mediated haemolysis masquerading as cold agglutinin-induced anaemia complicating severe infection with mycoplasma pneumoniae.

Haemolytic anaemia complicating Mycoplasma infection has usually been attributed to IgM cold agglutinins. This report describes a patient with pneumonia due to Mycoplasma pneumoniae in whom severe haemolysis persisted despite declining thermal amplitude and titre of cold agglutinins as the infection resolved. Class-specific anti-globulin (Coombs) testing defined an IgG warm agglutinin coating the patient's erythrocytes that was distinct from the IgM cold agglutinin identified by Sephadex G-200 gel filtration and dithiothreitol inactivation. Monoclonal IgM(gamma) and IgK(k) circulating proteins were identified and immuno-electrophoresis of the cold agglutinin-containing cryoglobulin fraction identified the cold agglutinin as an IgM(gamma). In this patient initially presumed to have cold agglutinin induced haemolysis secondary to Mycoplasma infection, an IgG warm agglutinin was identified as the aetiology for the patient's haemolysis, underscoring the clinical relevance of careful evaluation of the mechanism of haemolysis accompanying Mycoplasma pneumonia.