When to refer a patient to hematology for elevated hemoglobin (H/H) levels?

When to Refer to Hematology for Elevated Hemoglobin/Hematocrit

Patients with elevated hemoglobin/hematocrit should be referred to hematology when there are concerning features suggesting polycythemia vera or other myeloproliferative neoplasms, including elevated red blood cell count >6.45×10¹²/L, platelets >350×10⁹/L, or neutrophils >6.2×10⁹/L. 1

Urgent Referral Indications

• Hemoglobin >18.5 g/dL in men or >16.5 g/dL in women with symptoms of hyperviscosity (headaches, blurred vision, thrombotic events) 2
• Elevated hemoglobin with abnormal peripheral blood smear showing immature myeloid cells or dysplastic features 2
• Elevated hemoglobin with splenomegaly or other clinical features suggesting myeloproliferative neoplasm 2
• Elevated hemoglobin with positive JAK2 mutation testing 1, 3

Standard Referral Indications

• Persistently elevated hemoglobin (>16.5 g/dL in men or >16.0 g/dL in women) without obvious secondary cause 2
• Elevated hemoglobin with elevated red blood cell mass confirmed by testing 2
• Elevated hemoglobin with low erythropoietin level 1
• Elevated hemoglobin with thrombotic events or history of thrombosis 2

Laboratory Findings That Should Prompt Referral

• Elevated red blood cell count >6.45×10¹²/L 1
• Elevated platelets >350×10⁹/L (suggesting possible myeloproliferative disorder) 1
• Elevated neutrophils >6.2×10⁹/L (suggesting possible myeloproliferative disorder) 1
• Presence of JAK2 V617F or exon 12 mutations 3
• Presence of additional mutations such as TET2, DNMT3A, or ASXL1 (found in 34.5% of JAK2-positive patients) 3

Initial Evaluation Before Referral

• Complete blood count with differential 1
• Peripheral blood smear examination 2
• Serum erythropoietin level 1
• JAK2 V617F mutation testing (consider using the JAKPOT prediction rule to determine need for testing) 1
• Oxygen saturation and arterial blood gas (if hypoxia suspected) 2

Clinical Decision Algorithm

1. Determine if hemoglobin is truly elevated:

   • Men: >16.5 g/dL
   • Women: >16.0 g/dL 4

2. Rule out secondary causes:

   • Dehydration
   • High altitude
   • Smoking
   • Chronic lung disease
   • Sleep apnea 2

3. Apply the JAKPOT prediction rule - refer if ANY of the following are present:

   • Red blood cell count >6.45×10¹²/L
   • Platelets >350×10⁹/L
   • Neutrophils >6.2×10⁹/L 1

4. Consider immediate referral if:

   • Positive JAK2 mutation
   • Symptoms of hyperviscosity
   • Thrombotic events
   • Splenomegaly 2, 3

Common Pitfalls to Avoid

• Failing to distinguish between absolute erythrocytosis (true increase in red cell mass) and relative erythrocytosis (plasma volume contraction) 1
• Overlooking secondary causes of erythrocytosis before referral 2
• Not considering JAK2 mutation testing in patients with persistently elevated hemoglobin 3
• Focusing only on hemoglobin without evaluating other blood cell lines (platelets, white blood cells) 1
• Assuming all elevated hemoglobin cases require hematology referral - applying the JAKPOT rule could reduce unnecessary referrals by over 50% 1

Importance of Early Detection

• Early identification of polycythemia vera is critical as it can lead to serious complications including thrombosis and hemorrhage 3
• Patients with JAK2 mutations and additional mutations (particularly ASXL1) have worse prognosis and may require more aggressive management 3
• Unexplained erythrocytosis may be the first sign of an underlying myeloproliferative neoplasm 2, 3