What is the harm of high mean platelet volume needs to be combined with other test results of the patient, such as platelet count (PLT) index. If only the performance of the average platelet volume (MPV) is a little high, generally does not have any harm, if accompanied by PLT is not normal, it may be suffering from disease. 1. If the patient only has a slightly high mean platelet volume (MPV), it may be a temporary blood concentration caused by heavy exercise and low water intake, and can be observed for a few days and then reviewed. If the results of MPV and PLT are normal at the time of review, there is no need to deal with it, and there is no harm to the body in general. 2. If the high mean platelet volume is accompanied by abnormal PLT, it may be seen in the following three situations. (1) High MPV and low PLT: Commonly seen in cardiogenic hypertrophic osteoarthropathy, acute myocarditis, pre-eclampsia, immune thrombocytopenic purpura, and diabetes mellitus. (2) High MPV and normal PLT: common in myelofibrosis, splenectomy, chronic myelogenous leukemia, and some α- and β-thalassemia. (3) High MPV and elevated PLT: Commonly found in splenectomy, chronic granulocytic leukemia, and reactive thrombocytosis and iron deficiency. Therefore, when high mean platelet volume is detected, a doctor should be consulted for further diagnosis.