At what hemoglobin level should a patient be referred to hematology?

When to Refer to Hematology for Elevated Hemoglobin

Patients should be referred to hematology when hemoglobin levels exceed 16.5 g/dL in women or 18.5 g/dL in men, or at lower levels if accompanied by symptoms of hyperviscosity or risk factors for polycythemia. 1

Understanding Elevated Hemoglobin

Elevated hemoglobin (erythrocytosis) requires careful evaluation to distinguish between relative and absolute erythrocytosis, and to determine if it's primary or secondary:

• Hemoglobin levels above normal range (>16.5 g/dL in women, >18.5 g/dL in men) warrant investigation for underlying causes 1, 2
• Symptoms of hyperviscosity (headache, dizziness, visual disturbances, fatigue) at any hemoglobin level should prompt referral 3
• Patients with hemoglobin >20 g/dL or hematocrit >65% require urgent evaluation due to increased risk of thrombotic events 3

Specific Referral Thresholds

Absolute Indications for Referral:

• Hemoglobin >20 g/dL or hematocrit >65% (urgent referral) 3
• Persistent elevation of hemoglobin >18.5 g/dL in men or >16.5 g/dL in women after exclusion of common causes 1
• Any elevated hemoglobin with symptoms of hyperviscosity 3
• Elevated hemoglobin with splenomegaly, suggesting possible myeloproliferative neoplasm 3
• Elevated hemoglobin with thrombotic events 3

Consider Referral When:

• Elevated hemoglobin persists after addressing common causes (smoking, dehydration, high altitude, COPD) 1
• Young adults (<35 years) with unexplained erythrocytosis 1
• Family history of polycythemia or early thrombotic events with elevated hemoglobin 3
• Elevated hemoglobin with abnormal blood counts in other cell lines (thrombocytosis, leukocytosis) 3

Initial Evaluation Before Referral

Primary care providers should consider these steps before referral:

• Confirm true erythrocytosis by repeating CBC when patient is well-hydrated 1
• Rule out relative erythrocytosis due to dehydration, diuretics, or plasma volume contraction 1
• Screen for common secondary causes:
  • Smoking history (carbon monoxide exposure) 1
  • Pulmonary disease (COPD, sleep apnea) 1
  • Residence at high altitude 1
  • Medications (testosterone, erythropoietin) 3

Special Populations

Congenital Heart Disease Patients:

• Refer when hemoglobin >20 g/dL and hematocrit >65% with symptoms of hyperviscosity 3
• Avoid routine phlebotomies in cyanotic heart disease patients unless symptomatic 3

Polycythemia Vera Suspicion:

• Refer for JAK2 mutation testing when hemoglobin >16.5 g/dL in women or >18.5 g/dL in men with no obvious secondary cause 3
• Immediate referral for patients with elevated hemoglobin and thrombotic complications 3

Elderly Patients:

• Consider that hemoglobin levels normally decrease with age, so elevated levels in elderly patients are particularly concerning 4
• Hemoglobin >17 g/dL in elderly patients with heart failure is associated with increased mortality and should prompt referral 5

Management Considerations

• Therapeutic phlebotomy is indicated for hemoglobin >20 g/dL or hematocrit >65% with symptoms of hyperviscosity 3
• Repeated routine phlebotomies should be avoided due to risk of iron depletion unless directed by hematology 3
• In polycythemia vera, target hematocrit should be <45% to reduce thrombotic risk 3
• Patients with elevated hemoglobin due to chronic hypoxemia require different management than those with primary polycythemia 3

Remember that while these guidelines provide general thresholds, the presence of symptoms, risk factors, or comorbidities may warrant referral at lower hemoglobin levels. Early consultation with hematology can help establish appropriate monitoring and management strategies.