A low platelet count of 66 x 10^9/L may be due to diseases such as idiopathic thrombocytopenic purpura, aplastic anemia, and myelodysplastic syndrome. It may also be caused by certain drugs such as sulfonamide, chloramphenicol, or when hypersplenism or splenomegaly is caused by various reasons, resulting in a decrease in the number of platelets in the blood. 1. Idiopathic Thrombocytopenic Purpura: This disease is due to the thrombocytopenia caused by unknown reasons, often with bleeding, skin purpura, bleeding gums, nosebleeds and other symptoms. 2. Aplastic dysplastic anemia: it is a bone marrow hematopoietic failure disorder, which is manifested by the decrease of whole blood cells, in which thrombocytopenia will lead to the symptoms of skin and mucous membrane bleeding. 3. Myelodysplastic syndrome: it is originated from hematopoietic stem cells, the cells are sickly hematopoietic, which leads to the reduction of the three lineages in the blood, and thrombocytopenia is one of the symptoms. Unexplained thrombocytopenia requires active medical treatment, bone marrow aspiration, exclusion of malignant diseases, clear diagnosis and targeted treatment.