Thrombocytosis (platelets > 450 G/L)

Laboratory tests

• FBC with blood film
• Serum ferritin
• CRP
• Serum creatinineif needednon-French guidelineThrombocytosis without an obvious reactive cause on history and examination: these tests appear in the work-ups of the British primary care pathways ^[2,3]. A raised alkaline phosphatase with thrombocytosis further increases the probability of cancer ^[2].
• ASTif needednon-French guidelineThrombocytosis without an obvious reactive cause on history and examination: these tests appear in the work-ups of the British primary care pathways ^[2,3]. A raised alkaline phosphatase with thrombocytosis further increases the probability of cancer ^[2].
• ALTif needednon-French guidelineThrombocytosis without an obvious reactive cause on history and examination: these tests appear in the work-ups of the British primary care pathways ^[2,3]. A raised alkaline phosphatase with thrombocytosis further increases the probability of cancer ^[2].
• GGTif needednon-French guidelineThrombocytosis without an obvious reactive cause on history and examination: these tests appear in the work-ups of the British primary care pathways ^[2,3]. A raised alkaline phosphatase with thrombocytosis further increases the probability of cancer ^[2].
• Alkaline phosphataseif needednon-French guidelineThrombocytosis without an obvious reactive cause on history and examination: these tests appear in the work-ups of the British primary care pathways ^[2,3]. A raised alkaline phosphatase with thrombocytosis further increases the probability of cancer ^[2].
• LDHif needednon-French guidelineThrombocytosis without an obvious reactive cause on history and examination: these tests appear in the work-ups of the British primary care pathways ^[2,3]. A raised alkaline phosphatase with thrombocytosis further increases the probability of cancer ^[2].
• Serum calcium (if no obvious cause)if needednon-French guidelineUnexplained thrombocytosis: serum calcium is among the tests suggested by the York pathway ^[3].

Imaging

• Chest X-ray (aged 40 or over, unexplained thrombocytosis)if needednon-French guidelinePatient aged 40 or over with thrombocytosis: NICE proposes considering an urgent chest X-ray to look for lung cancer ^[4]; the Lothian pathway requests it when no symptom points to another cancer ^[2].

In 4 to 6 weeks

• FBC (repeat)

Laboratory tests

• FBC with blood film
• Serum ferritinif needednon-French guidelineHaematology advice for persistent thrombocytosis presupposes a normal CRP and ferritin ^[3].
• CRPif needednon-French guidelineHaematology advice for persistent thrombocytosis presupposes a normal CRP and ferritin ^[3].
• JAK2 V617F mutation (not in the French laboratory fee schedule: not reimbursed in community practice; preferably by the haematologist)if needednon-French guidelinePersistent thrombocytosis without a reactive cause, when referring for suspected myeloproliferative neoplasm: the GP can send the JAK2 test with the request for advice ^[3].
• CALR and MPL mutations (if JAK2 negative; not in the French laboratory fee schedule, by the haematologist)if needednon-French guidelineJAK2 testing negative in a patient suspected of essential thrombocythaemia: CALR and MPL are the two other driver mutations of the WHO criterion ^[12]. Specialist test, to be left to the haematologist.
• BCR-ABL transcript (to rule out chronic myeloid leukaemia; preferably at the haematologist's initiative)if needednon-French guidelineThe German DGHO (2023) looks for it at the same time as JAK2, CALR and MPL ^[13]; the WHO criteria require exclusion of BCR-ABL1-positive chronic myeloid leukaemia ^[12]. NABM procedure 1035 covers the diagnosis and follow-up of this leukaemia ^[9].

• Platelets > 1000 G/L, recent arterial or venous thrombosis, neurological signs or bleeding: rapid haematology opinion, possibly the same day.