Hemolysis is the premature destruction of red blood cells. Normally they live about 120 days; in hemolysis they die sooner, and the bone marrow cannot always keep up with the loss — then hemolytic anemia develops.
When the cells break down, hemoglobin and its breakdown products are released into the blood, producing characteristic changes on lab tests.
What hemolysis is
Destruction can occur inside the vessels (red blood cells burst right in the bloodstream) or in the spleen and liver (cells are captured by macrophages). In both cases hemoglobin is released, part of which turns into unconjugated bilirubin — hence possible jaundice and darkening of the urine.
Causes
Hemolysis can be inherited (defects of the red blood cell membrane or hemoglobin — for example, sickle cell anemia and thalassemias, G6PD enzyme deficiency) or acquired: autoimmune reactions, infections, certain drugs and toxins, mechanical damage (artificial heart valves), an incompatible blood transfusion, and microthrombi in small vessels.
How to recognize it from lab tests
Hemolysis is indicated by a combination of signs: a drop in haptoglobin (it binds free hemoglobin and is used up quickly), a rise in LDH and unconjugated bilirubin, and an increase in reticulocytes — young red blood cells the bone marrow makes to compensate for the loss. The Coombs test clarifies the cause of autoimmune hemolysis.
Reference ranges
Typical laboratory signs of active hemolysis:
| Haptoglobin | reduced or undetectable |
| LDH | elevated |
| Unconjugated bilirubin | elevated |
| Reticulocytes | elevated |
Frequently asked questions
Are hemolysis in the test tube and hemolysis in the body the same thing?
No. The lab sometimes reports a 'hemolyzed sample' — this is the destruction of red blood cells during improper blood collection; it distorts results but is not a disease. This article is about hemolysis in the body.
Does hemolysis always lead to anemia?
Not always. If the bone marrow can ramp up red blood cell production, hemoglobin stays normal (compensated hemolysis). Anemia appears when destruction outpaces recovery.