The relative density of platelets in a normal human is 1.030-1.060. Below 1.030 is a decrease in platelet relative density, and above 1.060 is an increase in platelet relative density. The decrease in platelet relative density is commonly caused by various reasons, such as immune thrombocytopenic purpura, aplastic anemia, myelodysplastic syndrome, multiple myeloma, various acute leukemias and so on, all of which will have a decrease in platelet relative density due to a decrease in the number of platelets. After the platelet count decreases, the body’s hemostatic function decreases, and bleeding occurs. Increased platelet relative density is commonly seen in various causes of increased platelet count, the most common clinically is primary thrombocytosis, where the platelet relative density can reach an abnormally high level.