What is the minimum hemoglobin (Hb) level required before starting phlebotomy?

Hemoglobin Threshold for Initiating Phlebotomy

Phlebotomy should be initiated when hemoglobin is ≥20 g/dL (with hematocrit >65%) in adults with congenital heart disease and hyperviscosity symptoms, or when hematocrit is >65% before noncardiac surgery; for hemochromatosis, phlebotomy begins regardless of hemoglobin level as long as hemoglobin is adequate to tolerate the procedure (typically ≥11-12 g/dL). 1, 2

Context-Specific Thresholds

For Erythrocytosis/Polycythemia (Congenital Heart Disease)

Symptomatic patients:

• Initiate phlebotomy when hemoglobin >20 g/dL AND hematocrit >65% in patients experiencing hyperviscosity symptoms (headache, lethargy) after excluding dehydration and iron deficiency 1
• These thresholds represent Class IIa evidence (reasonable to perform) 1

Pre-surgical patients:

• Perform phlebotomy when hematocrit >65% before noncardiac surgery, regardless of symptoms 1
• For testosterone-induced erythrocytosis, intervention is warranted at lower thresholds (hematocrit >50%) before surgery to reduce viscosity-related cardiovascular risks 2

Do NOT phlebotomize:

• Patients with hemoglobin <20 g/dL and/or hematocrit <65% who lack hyperviscosity symptoms (Class III recommendation - not indicated) 1

For Hemochromatosis/Iron Overload

Minimum hemoglobin to safely perform phlebotomy:

• Check hemoglobin/hematocrit before each phlebotomy session 1
• Pause phlebotomy if hemoglobin falls below 11 g/dL 1
• Reduce phlebotomy rate if hemoglobin falls below 12 g/dL 1
• Do not allow hemoglobin/hematocrit to fall by more than 20% from baseline 1

When to initiate treatment:

• Begin weekly phlebotomy in all patients with confirmed hemochromatosis and iron overload (elevated ferritin), regardless of baseline hemoglobin level, as long as hemoglobin is adequate 1, 3
• A hemoglobin threshold of 12.5 g/dL has been used successfully in hemochromatosis blood donor programs 4

Critical Safety Parameters

Monitoring requirements:

• Measure hemoglobin/hematocrit immediately before each phlebotomy to prevent excessive anemia 1, 3
• In hemochromatosis patients with cardiac disease (arrhythmias, cardiomyopathy), use slower phlebotomy schedules due to increased risk of sudden death with rapid iron mobilization 1, 3

Volume considerations:

• Standard phlebotomy removes 500 mL blood (containing 200-250 mg iron) 1
• Smaller volumes may be appropriate for patients with borderline hemoglobin levels 1

Common Pitfalls to Avoid

• Do not confuse the indication: The hemoglobin threshold for erythrocytosis/polycythemia (≥20 g/dL) is completely different from the minimum safe hemoglobin needed to tolerate phlebotomy in hemochromatosis (≥11-12 g/dL) 1
• Do not ignore symptoms: In congenital heart disease, phlebotomy at hemoglobin >20 g/dL is only indicated if hyperviscosity symptoms are present AND dehydration/iron deficiency are excluded 1
• Do not proceed with inadequate hemoglobin: Performing phlebotomy when hemoglobin is <11 g/dL risks symptomatic anemia and poor tolerance 1
• Do not use liberal thresholds pre-operatively: Surgical patients require more aggressive reduction of hematocrit to <50-65% depending on the clinical context 1, 2