At what hematocrit (Hct) level should a patient be referred to a hematologist for suspected erythrocytosis?

Referral Thresholds for Erythrocytosis to Hematology

Patients should be referred to a hematologist when the hematocrit is >45% for men or >42% for women with symptoms of hyperviscosity, or when hematocrit exceeds 60% for men and 55% for women regardless of symptoms. 1

Diagnostic Approach to Erythrocytosis

Initial Assessment

• Confirm true erythrocytosis (not relative polycythemia from dehydration)
• Check hematocrit levels:
  • Men: >45% warrants investigation
  • Women: >42% warrants investigation
  • Absolute referral threshold: >60% for men, >55% for women (always indicates absolute polycythemia) 2

Key Symptoms Requiring Prompt Referral

• Hyperviscosity symptoms:
  • Headache
  • Poor concentration
  • Fatigue
  • Visual disturbances
  • Dizziness

Risk Stratification for Referral

High Priority Referral (Immediate)

• Hematocrit >60% in men or >55% in women
• Any hematocrit elevation with:
  • Splenomegaly
  • Elevated white blood cell count
  • Thrombocytosis
  • Symptoms of hyperviscosity
  • History of thrombotic events

Standard Referral

• Persistent hematocrit >45% after addressing potential secondary causes:
  • Smoking cessation
  • Treatment of underlying pulmonary disease
  • Ruling out sleep apnea
  • Addressing high altitude exposure

Differentiating Types of Erythrocytosis

Primary Erythrocytosis

• Polycythemia vera (PV) - most common primary cause
• Characterized by:
  • Low serum erythropoietin
  • JAK2 mutations
  • Splenomegaly
  • Elevated white blood cells and/or platelets

Secondary Erythrocytosis

• Caused by external stimuli to bone marrow
• Characterized by normal or elevated erythropoietin levels
• Common causes:
  • Chronic hypoxemia (COPD, sleep apnea)
  • Congenital heart disease with right-to-left shunts
  • High altitude
  • Smoking
  • Certain medications

Management Before Referral

• For hematocrit <45%, monitor and address underlying causes
• For hematocrit >45% with symptoms or >60% without symptoms:
  • Consider therapeutic phlebotomy if symptoms of hyperviscosity are present
  • Avoid routine phlebotomies due to risk of iron depletion 1
  • Maintain adequate hydration
  • Check iron status (microcytosis suggests iron deficiency)

Special Considerations

Cyanotic Congenital Heart Disease

• Phlebotomy only indicated when:
  • Hematocrit >65% AND
  • Symptomatic (headache, poor concentration) AND
  • No dehydration or anemia 1

Polycythemia Vera Management

• Requires specialized care
• Phlebotomy to maintain hematocrit <45%
• Consider cytoreductive therapy for high-risk patients 1

Common Pitfalls to Avoid

1. Inappropriate phlebotomies: Routine phlebotomies without symptoms can lead to iron deficiency, decreased oxygen-carrying capacity, and increased stroke risk 1

2. Overlooking secondary causes: Always investigate for smoking, COPD, sleep apnea before referral

3. Ignoring symptoms: Even with borderline hematocrit elevation, hyperviscosity symptoms warrant referral

4. Failing to check erythropoietin levels: Low levels suggest primary erythrocytosis, while normal/high levels suggest secondary causes 3

5. Missing congenital causes: Consider genetic testing in young patients or those with family history 4

By following these guidelines, primary care providers can appropriately identify patients who need hematology referral for erythrocytosis, ensuring timely diagnosis and management to prevent complications related to hyperviscosity and thrombosis.