What are the selection criteria for blood transfusion in patients with polycythemia?

Blood Transfusion in Polycythemia Vera: Generally Contraindicated

Blood transfusions are contraindicated in polycythemia vera because they would further increase red cell mass and exacerbate hyperviscosity, potentially increasing thrombotic risk. 1

Core Principle: PV is a Disease of Excess, Not Deficiency

• Polycythemia vera is characterized by excessive red blood cell production leading to increased blood viscosity, which is the limiting factor in oxygen delivery to tissues 1
• The primary treatment goal is to reduce hematocrit below 45% through phlebotomy and cytoreductive therapy to prevent thrombotic complications 2, 1
• Adding blood products directly contradicts the fundamental pathophysiology and therapeutic approach 1

Exceptional Circumstances Where Transfusion May Be Considered

Transfusions should only be considered in rare, specific clinical scenarios 1:

Red Blood Cell Transfusions

• Acute perioperative blood loss requiring immediate replacement when phlebotomy has created relative anemia and surgical hemorrhage compounds this 1
• Development of secondary bone marrow failure where the disease has evolved and erythropoiesis has failed 1
• Transformation to myelofibrosis with cytopenias (post-PV myelofibrosis), where the disease has progressed from a proliferative to a fibrotic phase with resulting anemia 1

Platelet Transfusions

• Platelet transfusions should be avoided in PV patients with thrombocytosis 1
• PV patients may have qualitative platelet defects contributing to bleeding risk despite normal or elevated platelet counts 1
• Extreme thrombocytosis (>1,000-1,500 × 10⁹/L) paradoxically increases bleeding risk due to acquired von Willebrand disease, which occurs in more than one-third of PV patients with extreme platelet elevation 3, 4

Mandatory Precautions When Transfusion is Absolutely Necessary

If transfusion cannot be avoided, implement these safety measures 1:

1. Use leukoreduced blood products to minimize inflammatory reactions 2, 1
2. Administer small-volume transfusions with careful monitoring of hematocrit levels 1
3. Perform therapeutic phlebotomy before transfusion if the clinical situation allows, to maintain hematocrit below 45% 1
4. Continue low-dose aspirin therapy during the perioperative period to reduce thrombotic risk 1
5. Closely monitor hematocrit levels before, during, and after transfusion 1

Standard Management Instead of Transfusion

The appropriate management of PV involves reducing, not increasing, red cell mass 2, 1:

• Phlebotomy to maintain hematocrit <45% (definitively established by the CYTO-PV trial as superior for preventing thrombosis) 2, 3, 1
• Low-dose aspirin (81-100 mg/day) for all patients without contraindications 2, 3, 1
• Cytoreductive therapy (hydroxyurea or interferons) for high-risk patients (age >60 years and/or history of thrombosis) 2, 3, 1
• Ruxolitinib for patients who are resistant to or intolerant of hydroxyurea 1, 4

Critical Pitfall to Avoid

Do not transfuse PV patients based on a low hemoglobin number alone if that low hemoglobin resulted from appropriate therapeutic phlebotomy. The goal is intentional reduction of red cell mass to prevent thrombosis, which has a 20-year rate of 26% in PV 5. Transfusing these patients reverses the therapeutic benefit and increases their thrombotic risk 1.