Autoimmune haemolysis in the dog: relationship between anaemia and the levels of red blood cell bound immunoglobulins and complement measured by an enzyme-linked antiglobulin test.

A direct enzyme-linked antiglobulin test (DELAT) was used to measure the levels of red blood cell (RBC) bound IgG, IgM, IgA and C3 in dogs with autoimmune haemolytic anaemia (AIHA). At presentation, one or more DELAT parameters was raised in each AIHA case, and the RBC were typically coated with immunoglobulin of more than one class, together with C3. There was no relationship between the levels of RBC-bound IgG, IgM or IgA and the severity of the anaemia, although a significant negative correlation (rs = -0.66, P < 0.02) was found between bound C3 and blood haemoglobin concentration. These results indicate that the level of sensitisation of erythrocytes with IgG alone is not a reliable predictor of the severity of haemolysis in different cases, and that the pathogenesis of AIHA can be complex, involving multiple immunoglobulin classes and complement in the destruction of RBC. A significant relationship (rs = 0.63, P < 0.02) was found between serum IgG concentration and haemoglobin levels, and it is suggested that this may be due to free IgG inhibiting the interaction of IgG-sensitised RBC with macrophages. Serial measurements from individual AIHA cases during treatment revealed that the levels of RBC-bound immunoglobulins fell simultaneously with improvements in anaemia. In one dog, a relapse was associated with increases in bound IgG and IgM. Transient relative reticulocytopenia at presentation was common, but was not related to the severity of the anaemia. However, in other cases there was a persistent failure to increase RBC production, which was associated with slower recovery.