Hemolysis (alternative spelling haemolysis) is the excessive breakdown of red blood cells. When this happens, it causes a form of anemia.

Hemolysis is also an important factor in medical tests, as a blood sample may become hemolysed with prolonged storage, or during venipuncture. This may cause interference with the test results for a patient.

Hemolytic anemia

Normally, a red blood cell survives 90 to 120 days in circulation: about 1% of human red blood cells break down each day, which matches the production rate. The spleen (via the reticulo-endothelial system) is the primary organ by which red blood cells are cleared out of the circulation.

When the rate of breakdown increases, the body compensates by producing more red blood cells. If compensation is adequate there are few clinical problems.

If breakdown occurs at such a rate that it exceeds the body's ability to keep up, anemia develops.

Symptoms

Signs of anemia are generally present (fatigue, later heart failure). Hemolysis can be distinguished from other forms of anemia in several ways:

• certain aspects of the medical history can suggest a cause for hemolysis (drugs, fava bean or other sensitivity, prosthetic heart valve, or other serious medical illness)
• when peripheral blood smear is examined microscopically:
  • fragments of the red blood cells ("schistocytes") can be present
  • some red blood cells may appear smaller and rounder than usual (spherocytes)
  • reticulocytes are present in elevated numbers. This may be overlooked if a special stain is not used.
• The level of (unconjugated) bilirubin in the blood is elevated
• The level of lactate dehydrogenase (LDH) in the blood is elevated
• Haptoglobin levels are decreased
• Serologic antibody testing, specifically the direct Coombs test, can be abnormal. The Coombs test (Direct antiglobulin test/DAT) is positive when a patient's serum causes hemolysis in other samples, i.e. when the hemolysis is caused by auto-antibodies.

Causes of hemolysis

• Autoimmune disease (antibodies)
• Abnormal red cells, e.g., hereditary spherocytosis
  • Note that spherocytosis can be caused by both antibodies and a hereditary deficiency in a membrane-associated protein such as spectrin; in that case correct diagnosis requires the Coombs test.
• Drug + antibody (i.e., some drugs lead to haemolysis mediated by an antibody)
• G6PD deficiency and other enzyme deficiencies
• Mechanical (heart valves, extensive vascular surgery, microvascular disease)
• Toxins (e.g., snake venom)
• Blood transfusions from a non-compatible blood type

Differential diagnosis

• Ineffective hematopoiesis is sometimes misdiagnosed as hemolysis.
  • Clinically these conditions may share may features of hemolysis
  • Red cell breakdown occurs before a fully developed red cell is released into the circulation.
  • Examples: thalassemia, myelodysplastic syndrome
• Megaloblastic anemia due to deficiency in vitamin B12 or folic acid.

Therapy

Symptomatic treatment can be given by blood transfusion. Definitive therapy depends on the cause. In severe immune-related hemolytic anemia, steroid therapy is sometimes necessary.