What causes thrombocytosis (elevated platelet count)?

From the Guidelines

Thrombocytosis is primarily caused by secondary reactions to conditions such as inflammation, infection, and chronic inflammatory diseases, rather than primary bone marrow disorders. When considering the etiology of thrombocytosis, it's essential to differentiate between primary and secondary causes. Primary thrombocytosis, such as essential thrombocythemia, involves genetic mutations in blood-forming cells, leading to excessive platelet production 1. However, secondary thrombocytosis is more common and occurs as a response to other conditions, including inflammation, infection, iron deficiency anemia, and cancer 1.

Some key factors that contribute to secondary thrombocytosis include:

• Inflammation and infection, which can lead to increased platelet production as part of the body's healing process
• Chronic inflammatory conditions, such as rheumatoid arthritis, inflammatory bowel disease, and tuberculosis, which can cause elevated platelet counts
• Recent surgery, removal of the spleen, and certain medications, which can also contribute to thrombocytosis
• Intense exercise and high altitudes, which can lead to reactive thrombocytosis in some individuals

In the context of Kawasaki disease, thrombocytosis is a characteristic feature, typically occurring in the second week and peaking in the third week, with mean platelet counts reaching approximately 700,000 per mm3 1. This highlights the importance of considering the underlying cause of thrombocytosis, rather than just treating the elevated platelet count itself. By addressing the root cause, healthcare providers can develop effective treatment plans to manage thrombocytosis and improve patient outcomes.

From the Research

Causes of Thrombocytosis

Thrombocytosis, defined as a platelet count above 450×10^9/L, can occur as a primary or secondary event. The causes of thrombocytosis can be categorized into:

• Primary thrombocytosis:
  • Familial thrombocytosis
  • Essential thrombocythemia, a myeloproliferative neoplasm 2, 3, 4
• Secondary thrombocytosis:
  • Infection 5, 4, 6
  • Inflammation 2, 4, 6
  • Iron deficiency anemia 4, 6
  • Tissue injury 4
  • Malignancy 2, 5
  • Asplenia 2
  • Chronic inflammatory disorders 4
  • Exposure to high altitude 2

Characteristics of Thrombocytosis

The characteristics of thrombocytosis can vary depending on the underlying cause. For example:

• Primary thrombocytosis is often associated with a higher median platelet count and an increased incidence of thrombosis 4
• Secondary thrombocytosis is more common than primary thrombocytosis, and the major causes include tissue injury, infection, chronic inflammatory disorders, and iron deficiency anemia 4
• In children, secondary or reactive thrombocytosis is very common, occurring in 3-13% of hospitalized children, while primary thrombocytosis is extremely rare 6