An MPV blood test measures the average size of platelets in the blood. Platelets are small blood cells that stick together to form blood clots that stop or slow bleeding when you have a cut or injury. The test is often done as part of a complete blood count (CBC), which measures many different parts of the blood, including platelets. The MPV test can help diagnose bleeding disorders and diseases of the bone marrow. A low MPV indicates that the average platelet size is small, which may mean that a condition is affecting the production of platelets in the bone marrow. A high MPV indicates a high number of younger, larger platelets in the blood, which may be due to the bone marrow producing and releasing platelets rapidly into circulation. However, having a high or low MPV doesn’t mean anything on its own and should be interpreted within the context of other CBC results, such as platelet count. Your healthcare provider may order an MPV blood test as part of a routine exam or if you have symptoms of a blood disorder that may involve having too many or too few platelets.