Platelet count of 0.365% in a 4-year-old child is on the high side, the normal range is 0.1%~0.23%, which may be due to blood diseases or infectious diseases, as explained below. 1. Blood diseases: High platelet count can lead to high platelet count, such as chronic granulocytic leukemia, bleeding disorders and other blood diseases can lead to high platelet count, but these diseases are often accompanied by other indicators of abnormality, can not rely on this indicator to judge, need to go to the hospital in time to consult a specialist. 2. Infectious diseases: If the child suffers from chronic infectious diseases, most of the small blood vessels are broken, and the platelets will reactively increase to help local hemostasis, which will lead to high hematocrit, therefore, it is necessary to actively go to the hospital for consultation to clarify whether there are other chronic inflammatory diseases. If only one of the platelet counts is abnormal and the rest of the indicators are normal, then there is no need to worry too much, and you should consult a specialist after getting the report to avoid delaying your condition.