24th May 2023

Haemolytic Screen

Investigating haemolysis

Red blood cells have a lifespan of 120 days in the circulating bloodstream and are normally removed by macrophages in the spleen and liver. Premature destruction of red blood cells is termed haemolysis and leads to anaemia. There are several causes of haemolysis which can be classified based on the mechanism of red blood cell destruction.

A haemolytic screen is conducted when haemolysis is the suspected cause of anaemia and can help determine the underlying cause of haemolysis.

• Full blood count (including reticulocyte count)
  • Raised reticulocyte counts are seen in haemolysis as the body attempts to produce more red blood cells
• Peripheral blood film – to examine red blood cell morphology
• Liver function tests (including conjugated and unconjugated bilirubin i.e. “split bilirubin level”)
  • Hepatocytes are saturated in haemolysis and struggle to conjugate bilirubin, causing accumulation of unconjugated bilirubin in serum plasma
• Haptoglobin – a liver-produced protein that binds to free haemoglobin
  • Low levels in haemolysis
• Lactate dehydrogenase
  • Raised in haemolysis
• Direct antiglobulin test (DAT)

Direct Antiglobulin Test (Coomb’s Test)

This immunology laboratory test is used to determine if the cause of haemolysis is immune-mediated. Generally, immune haemolysis is due to antibody-mediated destruction of red blood cells. Antibodies that are directly attached to red blood cells result in a positive DAT. These antibodies can be auto-antibodies, as seen in autoimmune haemolytic anaemias, or, alloantibodies, seen in haemolytic transfusion reactions.