Warm AIHA

Question 1

What is Warm AIHA and how does it arise?

Answer 1

• Autoimmune haemolytic anaemia at warm temperatures.
• Production of IgG or IgA antibodies which bind to RBCs at 37 degrees. IgG are most common.
• Idiopathic in 50% of cases and due to an underlying condition, such as cancer, in the remaining 50%.
• Once the IgG antibodies have bound to the RBCs, this may or may not be accompanied by complement binding. These cells are then taken up by the RES macrophages via their receptors, where they are destroyed.
• This is a form of extravascular haemolysis.

Question 2

What are the symptoms and their explanations?

Answer 2

• Anaemia, fatigue, breathlessness – haemolysis of RBCs.
• Splenomegaly – increased RES mediated haemolysis.
• Jaundice – increased production of bilirubin due to breakdown of RBCs.
• These symptoms are all seen spontaneously at room temperature and at warmer temperatures.

Question 3

What are the laboratory findings?

Answer 3

• Anaemia – low RBCs and Hb
• Increased reticulocytes
• Blood film – spherocytes and schistocytes (RBC fragments)

Question 4

What further tests should be carried out?

Answer 4

• Positive DAT at 37 degrees – this can then be carried out with antibody/complement mixtures or either antibody or complement alone to determine what is binding to RBCs. Can be falsely negative if there are few antibodies, low affinity binding, if there is a different Ig present other than IgG and IgA, or temperature where assay carried out is too low.
• Biochemistry tests: LDH (increased), unconjugated and conjugated bilirubin.

Question 5

How is warm AIHA treated?

Answer 5

• 1st line: corticosteroids
• 2nd line: splenectomy
• Monoclonal antibodies e.g., rituximab to remove self-reactive B lymphocytes
• Treat the underlying cause, e.g., CLL
• Immunosuppressants, folic acid and transfusions in severe cases