From the Guidelines
The reduction in hematocrit in polycythemia vera is beneficial because it reduces blood viscosity. In polycythemia vera, the excessive production of red blood cells increases the blood's thickness or viscosity, which impairs blood flow through vessels and increases the risk of thrombosis 1. When the hematocrit is lowered through phlebotomy, the blood becomes less viscous, allowing it to flow more easily through blood vessels. This improved flow reduces the workload on the heart, decreases the risk of clot formation, and improves tissue perfusion. Key points to consider in the management of polycythemia vera include:
- The use of low-dose aspirin to prevent thrombotic complications, as established by the ECLAP trial 1
- Targeting hematocrit levels to <45% to lower the risk of thrombosis, as demonstrated by the CYTO-PV trial 1 While other options like increasing arterial oxygen saturation might seem plausible, the primary benefit of reducing hematocrit in polycythemia vera is specifically related to decreasing blood viscosity, which directly addresses the pathophysiological consequences of this myeloproliferative disorder. The most recent and highest quality study, the CYTO-PV trial 1, supports the recommendation to target a hematocrit level <45% to reduce the risk of thrombosis, thereby improving morbidity, mortality, and quality of life outcomes for patients with polycythemia vera.
From the Research
Reduction in Hematocrit Benefits
The reduction in hematocrit is beneficial because it:
Effects of Reduced Hematocrit
Reducing hematocrit to < 45% is associated with:
- Reduced rates of cardiovascular death and major thrombosis 2
- Decreased risk of thrombosis 2, 3, 4
- Improved management of polycythemia vera (PV) and essential thrombocythemia (ET) 3, 4
Treatment of Polycythemia Vera
Treatment of PV includes: