Platelet 9 usually refers to a platelet count of 9×10⁹/L, which indicates a low platelet count in the peripheral blood. The normal range of platelets is (100~300)×10⁹/L. Low platelet count may be caused by aplastic anemia, primary immune thrombocytopenia, leukemia and other diseases. 1. Aplastic anemia: aplastic anemia is mainly manifested by the decline of bone marrow hematopoietic function, when the disease attacks, it will affect the bone marrow hematopoietic function and cells of the whole body, triggering the body to appear anemia, bleeding and other phenomena. The number of platelets gradually decreases and the proportion of lymphocytes increases during routine blood tests. 2. Primary immune thrombocytopenia: it is a kind of hemorrhagic disease with unclear etiology, which is related to autoimmunity. When the disease attacks, it is mainly characterized by thrombocytopenia and normal or increased bone marrow megakaryocytes. Gum bleeding, skin ecchymosis and blood in stool will be shown. 3. Leukemia: generally there is no clear cause, it may be caused by genetic mutation of hematopoietic cells, and it is related to biological, physical and chemical factors, the most obvious symptoms are anemia, fever and infection, and proteinuria and hematuria, etc. Especially in the blood test, the disease is mainly characterized by thrombocytopenia, normal or increased bone marrow megakaryocytes, which is mainly characterized by gum bleeding, skin petechiae and blood in stool. The most obvious symptoms are anemia, fever, infection, proteinuria, hematuria, etc. Especially when doing routine blood tests, it is found that the platelet count in the blood is relatively low. When the platelet count is 9, it indicates that the platelets are seriously low, and it is necessary to go to the hospital for active treatment, such as platelet transfusion, etc., and actively improve the relevant examination and treatment for the cause of the disease, so as to avoid delaying the disease.