What volume of blood is required to reduce Red Blood Cell (RBC) Hemoglobin (Hgb) and Hematocrit (Hct)?

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Last updated: April 26, 2025 • View editorial policy

From the Guidelines

To reduce RBC Hgb and Hct, typically 1 unit of blood (approximately 450-500 mL) needs to be removed, always with an equal volume replacement of dextrose or saline, but only when the hemoglobin is more than 20 g/dL and the hematocrit is greater than 65% with associated symptoms of hyperviscosity and no evidence of dehydration 1.

Indications for Therapeutic Phlebotomy

The decision to perform therapeutic phlebotomy should be based on specific indications, including hemoglobin greater than 20 g per dL and hematocrit greater than 65%, associated with headache, increasing fatigue, or other symptoms of hyperviscosity in the absence of dehydration or anemia 1.

Risks of Repeated Phlebotomies

Repeated routine phlebotomies are not recommended due to the risk of iron depletion, decreased oxygen-carrying capacity, and stroke 1.

Management of Iron Deficiency

In cases where iron deficiency is identified, treatment should be cautious, especially in patients with destabilized erythropoiesis, and may involve oral or intravenous iron supplementation, with close monitoring of hemoglobin levels 1.

Key Considerations

  • The primary goal of therapeutic phlebotomy is to relieve symptoms of hyperviscosity, not to aggressively reduce RBC count, Hgb, and Hct levels.
  • The procedure should be performed with caution, considering the risks of iron depletion and decreased oxygen-carrying capacity.
  • Individualized treatment plans, including the volume and frequency of phlebotomy, should be determined by a healthcare provider based on the patient's specific condition and therapeutic goals.

From the Research

Reducing RBC Hgb and Hct through Blood Donation

To reduce Red Blood Cell (RBC) Hemoglobin (Hgb) and Hematocrit (Hct) levels, therapeutic phlebotomy is often used in patients with polycythemia vera. The goal of this treatment is to maintain a hematocrit level of less than 45% to decrease the risk of thrombosis.

Amount of Blood Needed

  • The amount of blood needed to achieve this goal can vary depending on the individual patient's condition and the frequency of phlebotomies required 2, 3.
  • Studies have shown that patients who require more frequent phlebotomies (3 or more per year) have a higher risk of thrombosis and may need to receive higher doses of hydroxyurea 3.
  • The European LeukemiaNet criteria recommend therapeutic phlebotomy to maintain a hematocrit level of less than 45% in all patients with polycythemia vera 4.

Treatment Patterns and Outcomes

  • A study of patients with polycythemia vera treated with hydroxyurea found that approximately one-third of patients had dose adjustments, and 18.6% discontinued hydroxyurea due to adverse events or lack of efficacy 5.
  • Another study found that hydroxyurea was associated with a lower incidence of fatal/non-fatal cardiovascular events and myelofibrosis transformation compared to phlebotomy alone 6.
  • The use of hydroxyurea in combination with phlebotomy may be beneficial in reducing RBC Hgb and Hct levels, but the optimal treatment approach should be individualized based on patient risk factors and response to therapy 2, 3, 4, 5, 6.

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.