Direct antiglobulin test negative, non spherocytic autoimmune haemolytic anaemia

We report a case of direct antiglobulin test (DAT) negative warm autoimmune haemolytic anaemia (AIHA). At initial presentation our patient had compensated haemolysis and was DAT positive for complement only. Severe haemolytic anaemia developed some years later with a negative DAT. Spherocytes were not a feature of the blood film and osmotic fragility studies were negative. Immune mediated haemolysis was confirmed by fluorescent activated cell sorter (FACS) analysis using antihuman IgG immunoglobulin. Response to immunosuppression was transient but a good response was achieved following splenectomy. Repeat FACS analysis post splenectomy demonstrated a marked rise in IgG coated red cells. Techniques used in establishing the diagnosis and possible mechanisms for this presentation are discussed.