Thrombocytosis means a platelet count above about 450,000 per microliter. Most cases are reactive, caused by infection, inflammation, iron deficiency, bleeding, cancer or loss of the spleen, while a smaller group comes from a bone marrow disorder such as essential thrombocythemia.
Key symptoms
- Usually none; found on a routine blood count
- Symptoms of the cause: fever, joint pain, weight loss, blood loss
- Headache, dizziness or vision changes in primary disease
- Burning pain in the hands and feet (erythromelalgia)
- Clots or, with very high counts, bleeding
What you find on exam
- Signs of infection, inflammation or cancer
- Enlarged spleen points to a marrow disorder
- Signs of clots: swollen leg, neurologic deficit
- Bruising or bleeding from the nose or gums
Tests
- Repeat blood count with peripheral smear
- Ferritin and iron studies; CRP and ESR for inflammation
- JAK2, CALR and MPL mutation tests if no reactive cause
- Bone marrow biopsy to confirm essential thrombocythemia; BCR-ABL to rule out chronic myeloid leukemia
Treatment basics
- Reactive: treat the underlying cause; the count usually falls on its own
- Essential thrombocythemia: low-dose aspirin for most patients
- Hydroxyurea for high-risk patients (age over 60 or past clot)
- Anagrelide or interferon as alternatives
- Check von Willebrand activity before aspirin when platelets are very high
Red flags
- Sudden weakness, chest pain or vision loss: arterial clot
- Swollen leg, shortness of breath or abdominal pain: venous clot
- Bleeding with platelets above 1,000,000 per microliter
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.