Should I refer an asymptomatic patient with persistent isolated thrombocytosis for two years and normal hemoglobin and white‑cell counts to hematology?

Hematology Referral for Persistent Isolated Thrombocytosis

Yes, refer this patient to hematology for evaluation of persistent thrombocytosis lasting two years, as this duration and pattern warrants investigation to differentiate between essential thrombocythemia and secondary causes, which has important implications for long-term thrombotic risk and management.

Clinical Context and Rationale

Your patient presents with isolated thrombocytosis (elevated platelets only) persisting for two years without symptoms and with normal hemoglobin and white blood cell counts. This clinical picture requires systematic evaluation to distinguish between:

• Essential thrombocythemia (ET) - a myeloproliferative neoplasm requiring long-term monitoring and potential treatment 1
• Secondary (reactive) thrombocytosis - which may resolve with treatment of underlying cause 1

Why Referral is Indicated

Duration and Persistence

• Thrombocytosis persisting for two years represents chronic elevation that moves beyond transient reactive causes 1
• The American Society of Hematology emphasizes that unexplained cytopenias or cytoses in any cell line should prompt hematology referral 2

Risk Assessment Considerations

• Essential thrombocythemia carries significant thrombotic risk, particularly arterial thrombosis, which is a key distinguishing feature from secondary causes 1
• Patients with ET have long-term risks requiring specialized monitoring and potential antiplatelet therapy or cytoreductive treatment 1

Diagnostic Complexity

• Differentiating ET from secondary thrombocytosis requires specialized evaluation including molecular testing for JAK2, CALR, and MPL mutations, which have an overall diagnostic yield of 52.4% in thrombocytosis cases 1
• Clinical characteristics alone are insufficient - molecular testing is often necessary but should be guided by clinical assessment to avoid overinvestigation 1

What the Hematologist Will Evaluate

Clinical Factors Suggesting Secondary Thrombocytosis

The hematologist will assess for:

• Active malignancy - strongly associated with secondary thrombocytosis 1
• Chronic inflammatory disease - common cause of reactive thrombocytosis 1
• Iron deficiency - frequently causes secondary thrombocytosis 1
• History of splenectomy - leads to persistent thrombocytosis 1
• Smoking history - relevant risk factor 1

Clinical Factors Suggesting Essential Thrombocythemia

• History of arterial thrombosis - significantly predictive of ET (p < 0.05) 1
• Higher hemoglobin levels - associated with ET 1
• Elevated mean corpuscular volume (MCV) - associated with ET 1
• Elevated red cell distribution width (RDW) - associated with ET 1
• Elevated mean platelet volume (MPV) - associated with ET 1

Laboratory Investigations

• Complete blood count with differential - to assess all cell lines 1
• Ferritin level - to exclude iron deficiency as a cause 1
• Peripheral blood smear review - to assess for morphologic abnormalities 1
• Molecular testing (JAK2, CALR, MPL mutations) - if clinical assessment suggests ET 1
• Bone marrow biopsy - may be needed in select cases for definitive diagnosis 1

Timing of Referral

• Standard (non-urgent) referral is appropriate for your asymptomatic patient with isolated thrombocytosis 2, 3
• This differs from thrombocytopenia, where platelet counts <20 × 10⁹/L require urgent referral within 24-72 hours 2, 3
• However, do not delay referral for months - aim for evaluation within 2-4 weeks given the two-year duration 2

Important Caveats

When to Expedite Referral

Refer more urgently if the patient develops:

• New thrombotic events (arterial or venous) 1
• Bleeding symptoms despite elevated platelets 4
• Progressive elevation in platelet count 2
• Development of other cytopenias or cytoses (bicytopenia or pancytopenia) 2
• Constitutional symptoms (fever, weight loss, night sweats) suggesting myeloproliferative disorder 5

Red Flags Requiring Immediate Evaluation

• Platelet count >2000 × 10⁹/L - may suggest chronic myeloid leukemia, particularly with elevated granulocyte counts 6
• White blood cell count >50 × 10⁹/L with thrombocytosis - concerning for chronic myeloid leukemia 6
• Splenomegaly on examination - argues against simple reactive thrombocytosis and suggests myeloproliferative neoplasm 7

Common Pitfalls to Avoid

• Do not assume thrombocytosis is benign simply because the patient is asymptomatic - ET patients may be asymptomatic until they develop thrombotic complications 1
• Do not order molecular testing without hematology consultation - a practical clinical approach can reduce unnecessary costly testing 1
• Do not wait for symptoms to develop before referring - the goal is to identify ET before thrombotic complications occur 1
• Do not overlook simple causes like iron deficiency, which should be checked before referral 1