(hē-mol′ĭ-sĭs )

[hemo- + -lysis]
The destruction of red blood cells (RBCs) because of RBC diseases, e.g., spherocytosis or sickle cell disease, or because of their exposure to drugs, toxins, artificial heart valves, antibodies, some infections, or snake venoms. Red cell membranes are destroyed directly or through antibody-mediated lysis. Donor antibodies in blood products cause hemolysis associated with transfusion reactions. Autoantibodies develop as the result of disease (esp. hematological cancers), in response to certain drugs (such as alpha-methyldopa), or in Rh-negative mothers carrying an Rh-positive fetus. Viral and bacterial infections are frequent causes of hemolysis in children, whose RBC membranes are very fragile. Organisms causing hemolysis include certain streptococci, staphylococci, and the tetanus bacillus. Hemolysis also occurs in smallpox and diphtheria and after severe burns.
When RBCs are destroyed, hemoglobin is released into plasma and filtered through the kidneys, turning the urine red (hemoglobinuria).

When hemolysis is gradual, patients may have mild breathlessness, intolerance of exercise, or fatigue. Laboratory tests show decreased RBC count, hemoglobin, haptoglobin, and hematocrit, and elevated levels of lactate dehydrogenase and unconjugated bilirubin. Fragments of RBCs may sometimes be seen in microscopically in blood smears.
SEE: autoantibody; SEE: fragility of red blood cells; SEE: hemolytic anemia