Causes of a high platelet count include cancer, recent spleen removal and anemia caused by premature destruction of the red blood cells, notes MedlinePlus. A normal platelet count ranges from 150,000 to 400,000 platelets per microliter of blood.
Allergic reactions, physical trauma and major surgery can cause a temporary elevation in platelet count, explains MedlinePlus. Additional causes of a high platelet count include polycythemia vera, primary thrombocythemia, chronic myelogenous leukemia and certain medications. Vincristine, tretinoin and epinephrine are some of the medications that affect platelet levels, states Mayo Clinic.
Polycythemia vera develops when the bone marrow produces too many red blood cells, states the National Cancer Institute. Because polycythemia vera sometimes affects the platelets, people with the condition are at risk for developing bleeding problems.
Primary thrombocythemia develops when the bone marrow starts making too many platelets for no apparent reason, reports MedlinePlus. The condition tends to worsen over time, leaving people with primary thrombocythemia at risk for bleeding disorders.
Chronic myelogenous leukemia affects the bone marrow, explains the American Cancer Society. One of the complications of the accelerated phase of CML is a very high platelet count. The number of platelets in the blood is one of the factors used to determine the prognosis of a patient.