When to refer a patient with thrombocytosis (elevated platelet count) to a hematologist (blood disorder specialist)?

When to Refer Thrombocytosis to a Hematologist

Refer patients with thrombocytosis (platelet count >450 × 10⁹/L) to hematology when: the elevation is unexplained, persists beyond 3 months, platelet count exceeds 1,000 × 10⁹/L, or when clinical features suggest primary thrombocytosis (myeloproliferative neoplasm).

Immediate Hematology Referral Criteria

Refer urgently (within 24-72 hours) if:

• Platelet count >1,000 × 10⁹/L (extreme thrombocytosis) - associated with higher thrombotic and bleeding risk, particularly in primary thrombocytosis 1, 2
• Symptomatic thrombocytosis with thrombotic events, microvascular symptoms (erythromelalgia, headaches, visual disturbances), or bleeding complications 3, 4
• Clinical features suggesting myeloproliferative neoplasm: splenomegaly, constitutional symptoms (night sweats, pruritus, fatigue), or unexplained leukocytosis 3, 1
• Persistent unexplained thrombocytosis without identifiable secondary cause after initial workup 2, 4

Risk Stratification Approach

Primary vs. Secondary Thrombocytosis

Primary thrombocytosis (12.5% of cases) requires hematology evaluation 1:

• Median platelet count significantly higher than secondary causes 1
• 86% have JAK2, CALR, or MPL mutations 1
• Higher thrombotic risk compared to secondary thrombocytosis 1, 4
• May present with paradoxical bleeding when platelets >1,500 × 10⁹/L 3, 4

Secondary thrombocytosis (83% of cases) typically does not require hematology referral if cause is identified 1:

• Common causes: tissue injury (32%), infection (17%), chronic inflammation (12%), iron deficiency (11%) 1
• Generally resolves with treatment of underlying condition 1, 2
• Lower thrombotic risk 1

Outpatient Evaluation Before Referral

For platelet counts 450-1,000 × 10⁹/L without symptoms, perform initial workup 1, 2:

• Review for secondary causes: recent surgery/trauma, active infection, inflammatory conditions, iron deficiency, malignancy, medications 1, 2
• Repeat platelet count in 2-4 weeks to confirm persistence 2
• Assess for MPN features: splenomegaly on exam, constitutional symptoms, complete blood count showing leukocytosis or erythrocytosis 3, 1

Refer to hematology if:

• Thrombocytosis persists >3 months without identified secondary cause 2
• No clear reactive etiology identified 2, 4
• Additional cytopenias or cytoses present 3

Special Populations

Pediatric Patients

• Thrombocytosis occurs in 3-13% of hospitalized children, usually reactive 2
• Refer if: elevation persists, is unexplained, symptomatic, or platelet count >1,000 × 10⁹/L 2
• Primary thrombocytosis extremely rare (1 per million children) 2

Pregnant Patients

• Immediate hematology referral required for any suspected MPN in pregnancy 3
• Requires specialized management with interferon-alpha if cytoreduction needed 3

Management Pending Hematology Evaluation

For high-risk features while awaiting hematology consultation 3, 4:

• Consider low-dose aspirin (81-100 mg daily) for patients with JAK2 mutation, cardiovascular risk factors, or microvascular symptoms 3
• Avoid aspirin if platelet count >1,500 × 10⁹/L due to acquired von Willebrand syndrome risk 3
• Manage cardiovascular risk factors aggressively: hypertension, diabetes, hyperlipidemia, smoking cessation 3

Common Pitfalls to Avoid

• Do not dismiss persistent thrombocytosis as "reactive" without thorough evaluation for secondary causes and follow-up platelet counts 1, 2
• Do not delay referral for extreme thrombocytosis (>1,000 × 10⁹/L) even if asymptomatic 1, 2
• Do not start aspirin without first ruling out acquired von Willebrand syndrome in patients with platelet counts >1,000 × 10⁹/L 3
• Do not assume reactive thrombocytosis in patients with splenomegaly or constitutional symptoms - these suggest primary MPN 3, 1