Autoimmune haemolytic anaemia (AIHA) results as a consequence to antibodies directed to the surface of red blood cells. Once the binding of antibody to the red blood cell occurs the erythrocyte is quickly removed from the circulation and destroyed (extravascular haemolysis). Alternatively, the red blood cells can be destroyed within the circulation by the activation of complement (intravascular haemolysis). Extravascular haemolysis occurs more commonly than intravascular haemolysis. Immune-mediated haemolysis is a feature of neonatal isoerythrolysis.
Primary AIHA are caused by direct autoantibodies directed towards healthy erythrocytes. Secondary AIHA results when the erythrocytes are bound to other antigens, making the erythrocytes appear foreign. There are a number of other disease processes that have been known to cause secondary AIHA. These include a range of bacterial infections (e.g., Streptococcus spp., Clostridium species), neoplasia ( most commonly lymphosarcoma), and secondary to a certain toxins and drugs. The drugs often implicated are penicillin and cephalosporins.
Signs of AIHA
The signs of AIHA are highly variable and dependent on the rate of the red blood destruction and the severity of the resulting anaemia. When rapid and severe the expected signs include increases in heart rate and respiratory rate, pale mucous membranes, cardiac murmur, weakness, tremor and collapse.
If the haemolysis is extravascular then the mucous membranes will be pale and icteric (jaundiced). If the haemolysis is intravascular the plasma and urine will be discoloured pink due to free pigment.
Any underlying disease process may result in other disease-specific clinical signs.
Diagnosis
There will be a broad decrease in red blood cell parameters and if severe spherocytes and erythrophagocytosis will be present. Some samples will autoagglutinate making analysis challenging.
A leucocytosis characterized by a mature neutrophilia is common. Acute phase proteins (fibrinogen and SAA) are typically increased.
A direct Coomb’s antiglobulin test is helpful but can be difficult to run in Australia at present. The patient’s washed red blood cells are incubated with antiserum directed towards IgG, IgM, and complement. A positive response (agglutination, cell clumping) will occur when the patient’s cells are bound to antibody.
The ideal method involves indirect immunofluorescence using flow cytometry to detect antibody-coated red blood cells.
Treatment
Discontinue any drugs that could be associated with AIHA.
Identify and treat any underlying condition that may be inducing secondary AIHA. Lymphoma/lymphosarcoma is a common cause.
Immunosuppressive doses of corticosteroids. These include dexamethasone or prednisolone.
Other immune suppressing drugs may be required. These include azathioprine and cyclophosphamide.
Blood transfusion may be required.
Dosing
Dosing information is intended for use by registered veterinarians or veterinary nurses. Equiimed assumes no responsibility for the information detailed below. Equiimed shall not be liable for any damages resulting from reliance on any information provided below, or by reason of any misstatement or typographical errors. Ultimately veterinarians should consult information provided by the manufacturer prior to use.
Tags: Haemolymphatic system