What CBC (complete blood count) thresholds for hemoglobin, hematocrit, and red blood cell count in men and women indicate the need for therapeutic phlebotomy?

Therapeutic Phlebotomy Thresholds for Erythrocytosis

Therapeutic phlebotomy ("blood dump") is indicated only when hemoglobin exceeds 20 g/dL AND hematocrit exceeds 65%, accompanied by documented symptoms of hyperviscosity, after confirming adequate hydration and excluding iron deficiency. 1, 2

Critical Thresholds and Indications

Absolute Requirements for Therapeutic Phlebotomy

All of the following criteria must be met simultaneously before performing phlebotomy 1, 2:

• Hemoglobin > 20 g/dL 1, 2
• Hematocrit > 65% 1, 2
• Documented hyperviscosity symptoms (headache, blurred vision, confusion, bleeding, poor concentration) 1, 3
• Adequate hydration confirmed (dehydration excluded) 1, 2
• Iron deficiency excluded (transferrin saturation ≥20%) 1, 2

Hyperviscosity Symptom Recognition

Symptoms warranting intervention include 3:

• Vision changes: blurred vision, visual impairment, retinal vein occlusion 3
• Neurologic symptoms: headache, dizziness, confusion, altered mental status, seizures 3
• Bleeding manifestations: spontaneous epistaxis, mucosal bleeding, easy bruising 3

Important caveat: Symptom severity does not correlate reliably with measured hematocrit levels, and iron deficiency produces identical symptoms but requires opposite management (iron supplementation, not phlebotomy). 2, 3

Phlebotomy Procedure When Indicated

When the above criteria are met 1, 2:

• Remove 300-450 mL of blood per session 2
• Always replace with equal volume of normal saline or dextrose to prevent hemoconcentration 1, 2
• Never perform phlebotomy without volume replacement, as this increases stroke risk 1, 2

What These Thresholds Do NOT Apply To

Polycythemia Vera (Primary Polycythemia)

Completely different thresholds apply 2, 4, 5:

• Target hematocrit strictly < 45% through regular phlebotomy 2, 5
• Lower target of ≈42% for women and African Americans 2
• This 45% threshold is based on the CYTO-PV trial showing 2.7% vs 9.8% thrombotic event rate (P=0.007) 2
• All PV patients also require low-dose aspirin (81-100 mg daily) 2, 5

Diagnostic Thresholds (Not Treatment Thresholds)

Values that trigger diagnostic workup for polycythemia vera 4, 5:

• Men: Hemoglobin ≥18.5 g/dL or hematocrit >52% 4, 5
• Women: Hemoglobin ≥16.5 g/dL or hematocrit >48% 4, 5

These diagnostic thresholds are far lower than the therapeutic phlebotomy thresholds and should not be confused. 4, 5

Contraindications to Routine Phlebotomy

Repeated routine phlebotomies are explicitly contraindicated in secondary erythrocytosis because they cause 1, 2:

• Iron depletion 1, 2
• Decreased oxygen-carrying capacity 1, 2
• Paradoxically increased stroke risk 1, 2
• Production of iron-deficient microcytic red cells with reduced deformability 1, 2

First-Line Management Before Considering Phlebotomy

For patients with elevated hematocrit and symptoms 2:

1. Aggressive rehydration with oral fluids or IV normal saline (first-line therapy) 2
2. Evaluate and correct iron deficiency if transferrin saturation <20% 1, 2
3. Treat underlying causes: smoking cessation, CPAP for sleep apnea, manage COPD 2
4. Adjust testosterone if causative (dose reduction or discontinuation) 2

Common Clinical Pitfalls

• Do not use hemoglobin/hematocrit thresholds alone without assessing symptoms, hydration status, and iron stores 1, 2
• Do not perform phlebotomy for values below Hgb 20 g/dL and Hct 65% in secondary erythrocytosis 1, 2
• Do not overlook iron deficiency, which mimics hyperviscosity but requires iron supplementation 1, 2
• Do not confuse diagnostic thresholds (Hgb >18.5 men, >16.5 women) with therapeutic phlebotomy thresholds 4, 5
• Mean corpuscular volume is unreliable for screening iron deficiency in erythrocytosis; use ferritin and transferrin saturation 2

When to Refer to Hematology

Immediate referral indicated for 2:

• JAK2 mutation positive 2
• Hemoglobin >20 g/dL with symptoms despite initial management 2
• Unexplained splenomegaly 2
• Cytopenias coexisting with erythrocytosis 2
• Diagnosis remains unclear after initial workup 2