Hemolytic anemia refers to anemia caused by the destruction of red blood cells. The presence of abnormal indicators is usually divided into the following causes: 1. Red blood cell destruction: including elevated total bilirubin in blood biochemistry, of which free bilirubin, i.e. indirect bilirubin, is predominant, and fragments of red blood cells remaining after the destruction of red blood cells can be seen in peripheral blood smears, and a decrease in hemoglobin can be observed in blood routine. In patients with intravascular hemolysis, elevated plasma free hemoglobin, iron-containing hemoglobinuria and hemoglobinuria are also observed. 2. compensatory hyperplasia of the red lineage: peripheral blood smears can be observed with increased counts of nucleated erythrocytes and reticulocytes, and active bone marrow proliferation. In addition, hemolytic anemia of different etiologies can show different findings, such as a positive direct anti-human globulin test in patients with autoimmune anemia, a positive cold agglutinin test in patients with cold antibody type autoimmune hemolysis, and a positive acid hemolysis test in patients with paroxysmal sleep hemoglobinuria, and a flow cytology test with CD55, CD59 negative cells The proportion of CD55 and CD59 negative cells increases.