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Phlebotomy for Polycythemia Vera: Why It Lowers Risk and How It Works

Feb 8, 2026

Key takeaways

  • In polycythemia vera (PV), maintaining hematocrit (Hct) <45% was associated with fewer cardiovascular deaths and major thrombotic events than a target of 45–50% in a randomized trial. [1]
  • Therapeutic phlebotomy is a clinician-directed procedure that removes a prescribed amount of blood to lower hematocrit. Typical session volumes are commonly ~500 mL, with ~250 mL used in selected patients based on body size or clinical factors. [2,3]
  • Phlebotomy schedules are individualized. Many people need more frequent sessions initially to reach target and then maintenance based on hematocrit monitoring and symptoms. [4]
  • Because repeated phlebotomy can lower iron stores, clinicians commonly monitor blood counts and iron parameters over time and adjust the plan to balance hematocrit control with tolerability. [2,3,4]

Overview

Phlebotomy (therapeutic venesection) is a direct way to lower hematocrit in PV. A randomized controlled trial (CYTO-PV) compared hematocrit targets and found that maintaining Hct <45% resulted in fewer cardiovascular deaths and major thrombotic events than maintaining Hct 45–50%. [1] Many clinical resources incorporate this target for adults, with personalization by the treating team. [4]

Why phlebotomy lowers risk in PV

PV increases red-cell mass and raises hematocrit. Lowering hematocrit reduces exposure to a level linked with higher rates of serious thrombotic outcomes in PV. The strongest evidence for the commonly used adult target comes from CYTO-PV. [1]

How often is phlebotomy needed?

Frequency varies widely. Many people require more frequent sessions initially to reach target, then maintenance based on periodic hematocrit monitoring. [4] If sessions become difficult to tolerate or very frequent, patients should discuss plan adjustments with their treating team. [4]

Side effects and how to avoid them

Short-term effects can include lightheadedness, fatigue, or bruising at the needle site. Practical steps that may help include hydrating and eating beforehand (when appropriate) and standing up slowly afterward.


Evidence from blood-removal settings suggests water ingestion can reduce vasovagal reactions in susceptible individuals. [5] (Your care team may tailor this advice based on medical conditions that require fluid limits.)

Iron depletion: monitored over time

Repeated phlebotomy can lower iron stores. Procedural reviews emphasize monitoring during ongoing phlebotomy programs, with adjustment of phlebotomy frequency/volume when clinically needed. [2,3] Practice guidance in PV and secondary erythrocytosis discusses avoiding routine iron supplementation unless there is a clear clinical indication and clinician supervision. [4]

Frequently asked questions (FAQs)

1. Why is the goal under 45%?

In a randomized PV trial, targeting Hct <45% reduced cardiovascular death and major thrombosis compared with a target of 45–50%. Many adult PV care plans therefore use <45% as a common target, with individualization by the treating team. [1,4]


2. How often will I need phlebotomy long term?

It varies. Many people need phlebotomy more frequently at the start to reach target and then as needed for maintenance based on hematocrit monitoring and symptoms. [4]


3. Should I take iron?

Not routinely without clinician guidance. Phlebotomy can lower iron stores, and care teams often monitor blood counts and iron measures over time. Decisions about iron supplementation should be individualized and supervised. [2,3,4]


4. What can I do to feel better after sessions?

Hydrate and eat beforehand when appropriate, and stand up slowly afterward. If you have dizziness or near-fainting, tell the care team so the procedure plan (volume, pace, positioning, fluids as appropriate) can be adjusted. Evidence from blood-removal settings suggests water ingestion can reduce vasovagal reactions in susceptible individuals. [5]


5. Is therapeutic phlebotomy the same as donating blood?

Therapeutic phlebotomy is medical treatment ordered and supervised as part of PV care. Donation policies vary by jurisdiction and organization, and blood removed from a person with PV may not be eligible for transfusion. Donation should not be used as a substitute for a PV management plan. [6,7]

References

  1. Marchioli, R., Finazzi, G., Specchia, G., Cacciola, R., Cavazzina, R., Cilloni, D., De Stefano, V., Elli, E., Iurlo, A., Latagliata, R., Lunghi, M., Lunghi, F., Polverelli, N., Rambaldi, A., Ruggeri, M., Randi, M. L., Santini, V., Vannucchi, A. M., … Barbui, T. (2013). Cardiovascular events and intensity of treatment in polycythemia vera. The New England Journal of Medicine, 368(1), 22–33. https://doi.org/10.1056/NEJMoa1208500
  2. Zubair, A. (2014). Therapeutic phlebotomy. Clinical Liver Disease, 4(5), 102–106. https://doi.org/10.1002/cld.408
  3. Kim, K. H., & Oh, K. Y. (2016). Clinical applications of therapeutic phlebotomy. Journal of Blood Medicine, 7, 139–144. https://doi.org/10.2147/JBM.S108479
  4. McMullin, M. F., Mead, A. J., Ali, S., Cargo, C., Chen, F., Ewing, J., Garg, M., Godfrey, A., Knapper, S., McLornan, D., Nangalia, J., Sekhar, M., Wadelin, F., & Harrison, C. N. (2019). A guideline for the management of specific situations in polycythaemia vera and secondary erythrocytosis: A British Society for Haematology Guideline. British Journal of Haematology, 184(2), 161–175. https://doi.org/10.1111/bjh.15647
  5. Lu, C.-C., Diedrich, A., Tung, C.-S., Paranjape, S. Y., Harris, P. A., Byrne, D. W., Jordan, J., & Robertson, D. (2003). Water ingestion as prophylaxis against syncope. Circulation, 108(21), 2660–2665. https://doi.org/10.1161/01.CIR.0000101966.24899.CB
  6. Joint United Kingdom (UK) Blood Transfusion and Tissue Transplantation Services Professional Advisory Committee (JPAC). (n.d.). Polycythaemia and raised haemoglobin. Retrieved February 11, 2026, from https://www.transfusionguidelines.org/dsg/wb/guidelines/po006-polycythaemia
  7. Australian Red Cross Lifeblood. (n.d.). I have polycythaemia (rubra) vera. Can I donate? Retrieved February 11, 2026, from https://www.lifeblood.com.au/faq/eligibility/medical-conditions-and-procedures/polycythaemia-rubra-vera