Low blood cells generally refer to lowered red blood cells, white blood cells, and platelets, and are usually associated with physiologic or pathologic causes. 1. Decrease in red blood cells (1) Physiological causes: infants and children aged 6 months to 2 years may be related to rapid growth and development; the elderly may be related to decreased hematopoietic function; women in the middle and late stages of pregnancy are related to increased blood volume. (2) Pathological causes: aplastic anemia, lack of iron, vitamin B12 and other hematopoietic substances or impaired utilization can cause a decrease in erythropoiesis; hereditary erythrocytosis, transfusion of incompatible blood groups can cause excessive destruction of erythrocytes; loss of erythrocytes due to trauma can cause erythropoiesis. 2. Decrease of white blood cells: it may be related to typhoid fever, influenza virus and other infections; it may be related to aplastic anemia and other blood diseases; it may also be related to long-term exposure to ionizing radiation and other physical and chemical injuries. 3. Reduced platelets: may be associated with aplastic anemia and other blood diseases leading to impaired production; hypersplenism and other leading to excessive destruction; thrombotic thrombocytopenic purpura and other leading to excessive consumption; splenomegaly and other leading to abnormal distribution. It can also be associated with pathologic causes such as congenital disorders such as neonatal thrombocytopenia. When a patient has low blood cells, the cause of the disease should be clarified under the guidance of a doctor and actively treated.