There are three reasons for low platelet density: decreased platelet production, increased destruction, and excessive consumption. Platelet density refers to the number of platelets in a unit volume, and population density is a concept. A high platelet density can be considered as a decrease in the number of platelets. The causes of platelet reduction are analyzed from the sources and destinations of platelets. The causes of decreased generation are mainly diseases with problems in bone marrow, such as aplastic anemia, leukemia, some tumors metastasizing to the bone marrow and so on. The main causes of increased destruction are idiopathic immune thrombocytopenia and destruction of platelets by drugs and toxins. The causes of excessive depletion include thrombotic thrombocytopenic violet epilepsy, DIC, etc., where platelets are depleted because of the formation of a large number of blood clots in the body. There are also diseases such as hypersplenism, massive blood loss, etc., which can also cause a decrease in platelets.