7 Common Causes of High Platelets (Thrombocytosis)

Platelets, or thrombocytes, are a type of cell present in the blood that help it to clot. These important cells clump together to stop bleeding and seal leakages in broken blood vessels. The platelet count of a healthy person is between 150, 000 to 450,000 [1] per microliter of blood. Significant fluctuations beyond either side of this range may be cause for concern.

A high platelet count is medically known as thrombocytosis or thrombocythemia. A high platelet count may be classified as primary thrombocythemia or secondary thrombocytosis. Primary or essential thrombocythemia is considered a condition by itself and the cause is unknown. Secondary or reactive thrombocytosis generally occurs as a symptom of other underlying medical conditions.

A high platelet count is often not a serious problem. Most people will experience no symptoms except the count is extremely high. In such cases, it can result in a lot of unpleasant symptoms. The blood may clot too often and unnecessarily, increasing the risk of bleeding, or of developing a stroke or heart attack.

Thrombocytosis is usually found in older people. Most diagnosis of thrombocytosis happens in people over the age of 60. Below are some of the causes:


Anemia is the medical term used to describe a shortage of red blood cells in the blood. Red blood cells carry oxygen and nutrients throughout the body. Hemoglobin is the oxygen-carrying protein present in these blood cells. It’s a common blood disorder that affects over three million people [2] in the United States. While mild in most cases, it can be a sign of more serious health conditions.

A high count of platelets, especially in relation to other blood cells, can be due to anemia. Sometimes this elevation platelets due to anemia is false. If you have hemolytic anemia, you may produce very small red blood cells. These cells may be wrongly counted as platelets during a full blood count.