High platelet counts (thrombocytosis) can happen for two main reasons:
- Primary thrombocytosis (essential thrombocythemia) where the bone marrow itself makes too many platelets due to a genetic mutation or problem in the marrow cells. This is a relatively rare blood disorder and sometimes considered a form of cancer.
- Secondary (or reactive) thrombocytosis, which is more common and occurs as a response to another condition or factor outside the bone marrow telling it to produce more platelets. Common causes include:
- Inflammation or infection
- Iron-deficiency anemia
- Cancer
- Blood loss or trauma
- Removal of the spleen
- Certain medications
- Chronic inflammatory diseases such as rheumatoid arthritis or inflammatory bowel disease
Most people with high platelets may not feel symptoms, and the count is often found by routine blood tests. Treatment depends on the cause, and many cases of secondary thrombocytosis resolve once the underlying issue is managed. In essence, your platelet count can be high either because your bone marrow is overproducing platelets on its own or because your body is reacting to another condition that stimulates platelet production.
