If platelets are high, it means that there are more than 450,000 platelets per microliter of blood, a condition known as thrombocytosis. Most high platelet counts are caused by a reactive process such as infection or inflammation, and once the underlying cause resolves or is managed, the platelet count returns to normal. However, if the platelet count remains elevated, it may signal an underlying condition that requires treatment.

If the platelet count is too high, blood clots can form in the blood vessels, which can block blood flow through the body and put the person at risk of life-threatening blood clots. Symptoms of high platelet levels often dont occur, but when they do, theyre often related to blood clots, such as headache, chest pain, shortness of breath, and weakness.

If a person has thrombocytosis, their healthcare provider will likely order a follow-up blood test a few weeks later to see if the levels remain high. If the levels remain elevated, the healthcare provider may prescribe medications and perform necessary procedures to prevent harmful blood clots. In emergencies, platelets can be filtered from the blood with a machine in a procedure called plateletpheresis.