At what hematocrit level is phlebotomy typically performed?

Phlebotomy Thresholds for Different Clinical Scenarios

Phlebotomy should be performed in patients with polycythemia vera (PV) to maintain a hematocrit level below 45%, while in patients with cyanotic congenital heart disease (CHD), phlebotomy is indicated when hematocrit exceeds 65% with associated hyperviscosity symptoms. 1

Polycythemia Vera

Recommended Hematocrit Thresholds

• Target hematocrit: <45% for all PV patients regardless of gender 1
• This target is based on the CYTO-PV study, which demonstrated reduced thrombotic events when hematocrit was maintained below 45%

Important Considerations

• While 45% is the standard target, individualization may be appropriate in specific situations:
  • For women, a lower target of 42% may be considered 1
  • For patients with progressive or residual vascular symptoms, a lower target may be warranted 1

Treatment Algorithm

1. Low-risk PV (age <60 years and no history of thrombosis):

   • Phlebotomy to maintain hematocrit <45% plus low-dose aspirin (81-100 mg/day) 1, 2

2. High-risk PV (age ≥60 years or history of thrombosis):

   • Phlebotomy to maintain hematocrit <45% plus low-dose aspirin AND cytoreductive therapy 1, 2
   • Hydroxyurea is the preferred first-line cytoreductive agent 2

Monitoring

• Evaluate hematocrit levels every 3-6 months or more frequently if clinically indicated 2
• Patients requiring ≥3 phlebotomies per year while on hydroxyurea therapy have been shown to have a higher risk of thrombosis (20.5% vs. 5.3% at 3 years) 3

Cyanotic Congenital Heart Disease

Recommended Hematocrit Thresholds

• Phlebotomy indicated when hematocrit >65% AND hemoglobin >20 g/dL with associated symptoms of hyperviscosity (headache, increasing fatigue) 1
• Phlebotomy indicated when hematocrit >65% before noncardiac surgery 1

Important Considerations

• Routine repeated phlebotomies are NOT recommended due to risk of iron depletion, decreased oxygen-carrying capacity, and stroke 1
• Always replace with equal volume of dextrose or saline when performing phlebotomy 1
• Phlebotomy is NOT indicated for patients with CHD, hemoglobin <20 mg/dL, and/or hematocrit <65% who have no hyperviscosity symptoms 1

Common Pitfalls to Avoid

1. Aggressive phlebotomy in cyanotic CHD patients

   • This can lead to iron deficiency, which reduces oxygen-carrying capacity and increases stroke risk 1

2. Failure to recognize iron deficiency in erythrocytosis

   • Iron-deficient red cells (microcytes) have reduced oxygen-carrying capacity and deformability 1
   • Monitor peripheral blood smear and serum ferritin or transferrin saturation

3. Ignoring gender differences in PV

   • Normal hematocrit ranges differ between men (42-54%) and women (38-46%) 1
   • Consider lower targets (42%) for women with PV 1

4. Inadequate monitoring of patients requiring frequent phlebotomies

   • Patients requiring ≥3 phlebotomies per year while on hydroxyurea have higher thrombotic risk and may need treatment adjustment 3

By following these evidence-based thresholds for phlebotomy, clinicians can optimize outcomes while minimizing complications associated with both excessive erythrocytosis and overly aggressive phlebotomy.