A PLT blood test measures the number of platelets in the blood, states MedlinePlus. Platelets help blood clot. Normal values range from 150,000 - 400,000 platelets per microliter of blood, though these reference ranges vary slightly between laboratories.
A low platelet count is called thrombocytopenia, according to Johns Hopkins Heart and Vascular Institute. Easy bruising and bleeding are the primary symptoms. The most common causes of thrombocytopenia include certain cancers, such as leukemias and lymphomas, medication side effects, kidney infection or dysfunction, chemotherapy and some inherited disorders. Too much alcohol can also lower platelet count. Severe cases may be treated with medication, blood transfusions, platelet transfusions or spleen removal, according to the National Institutes of Health.
A high platelet count is called thrombocytosis, states Johns Hopkins Heart and Vascular Institute. Blood clots in the extremities are the only symptoms. This spontaneous clotting can lead to heart attack or stroke. The most common causes include infections, anemia, some cancers and inflammation. Sometimes the cause is unknown. Thrombocytosis often resolves when the underlying cause is treated. Platelet pheresis may be used to treat severe cases. In this procedure, blood is removed, the platelets are separated out and the blood is returned to the body, thereby lowering platelet count.