What initial investigations should I perform to differentiate essential thrombocythaemia from secondary causes of thrombocytosis?

Initial investigations to differentiate essential thrombocythaemia (ET) from secondary causes of thrombocytosis primarily involve a comprehensive assessment to identify potential underlying conditions ¹.

• Clinical Assessment: Conduct an assessment to determine the possible underlying cause of thrombocytosis, as the underlying condition may be identified through this process ¹.
• Full Blood Count (FBC) Monitoring: If no underlying cause is identified and the person remains asymptomatic, repeat the full blood count in 4 to 6 weeks ¹. Persistent and unexplained thrombocytosis (over 450 × 10⁹/L for more than 3 months, or over 600 × 10⁹/L on at least two occasions 4–6 weeks apart, or within the range 450–600 × 10⁹/L with other haematological abnormalities) warrants referral to haematology for further investigation and management ¹.
• Investigation for Secondary Causes (e.g., Cancer): Consider the potential for a cancer diagnosis if a raised platelet count is found during a full blood count review ¹. Specific investigations may include:
  • An urgent chest X-ray for individuals aged 40 and over with thrombocytosis, to consider lung cancer ⁴.
  • A direct access ultrasound scan for women aged 55 and over with thrombocytosis and unexplained visible haematuria or vaginal discharge, to consider endometrial cancer ⁴.
  • Non-urgent, direct access upper gastrointestinal endoscopy for individuals aged 55 and over with a raised platelet count alongside symptoms such as nausea, vomiting, weight loss, reflux, dyspepsia, or upper abdominal pain, to consider oesophageal or stomach cancer ⁴.
• Haematology Referral for Specialist Investigations: Referral to a haematologist is indicated for people with high platelets and/or white count, enlarged spleen, family history of myeloproliferative disease, previous history of thrombosis, and altered erythropoietin levels, especially if a myeloproliferative disease is suspected ²,³. Specialist investigations, such as testing for the JAK2 V617F mutation and uncommon JAK2 exon 12 mutations, are carried out to definitively confirm or refute myeloproliferative diseases like polycythaemia vera, which is part of the differentiation process for essential thrombocythaemia ²,³.