What are the implications of elevated hematocrit (Hct)?

From the Guidelines

Elevated hematocrit should be managed by targeting hematocrit levels to <45% to lower the risk of thrombosis, as evidenced by the CYTO-PV trial 1. Elevated hematocrit refers to an abnormally high percentage of red blood cells in the total blood volume, typically above 48% in men or 45% in women. This condition requires medical evaluation to determine the underlying cause, which may include dehydration, living at high altitude, smoking, lung disease, heart disease, or blood disorders like polycythemia vera.

Key Considerations

• If you have elevated hematocrit, your doctor may recommend increasing fluid intake to address dehydration, or in more severe cases, therapeutic phlebotomy (removing blood) to reduce the hematocrit level, but only if 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.
• For polycythemia vera, medications like hydroxyurea (starting at 500-1000 mg daily) or interferon may be prescribed to suppress bone marrow production of red blood cells.
• Smoking cessation and oxygen therapy for those with lung disease can also help.
• Elevated hematocrit increases blood viscosity, which raises the risk of blood clots, stroke, and heart problems, making proper management important.
• Regular monitoring of complete blood counts is essential for those with chronic elevation, and aspirin (81-100 mg daily) may be recommended to reduce clotting risk in certain cases, as shown in the ECLAP trial 1.

Management Strategies

• Targeting a hematocrit level <45% can significantly reduce the composite primary endpoint of time until death from cardiovascular causes or major thrombotic events 1.
• Therapeutic phlebotomy should be used judiciously, as repetitive phlebotomies can deplete iron stores and result in production of iron-deficient red blood cells, which is undesirable due to reduced oxygen-carrying capacity and increased risk of stroke 1.

From the Research

Elevated Hematocrit Overview

• Elevated hematocrit is a characteristic of polycythemia vera, a Philadelphia negative myeloproliferative neoplasm 2
• The major cause of morbidity and mortality in polycythemia vera is thrombosis, which can be managed with aspirin and hematocrit reduction by venesection or cytoreductive therapy 2

Management of Elevated Hematocrit

• Hematocrit control below 45% is associated with a lower rate of thrombosis in polycythemia vera 3
• Phlebotomy and hydroxyurea are commonly used to manage elevated hematocrit in polycythemia vera patients 3, 4
• The need for additional phlebotomies during hydroxyurea therapy can identify patients with increased proliferation of polycythemia vera and higher risk of thrombosis 3

Treatment Options

• Hydroxyurea is a first-line cytoreductive therapy for high-risk polycythemia vera patients, but its use is associated with toxicities and resistance in some patients 2
• Interferon-α is an alternative treatment option for polycythemia vera patients, and has been shown to be effective in reducing thrombotic events and disease progression 5
• Phlebotomy has been shown to be associated with improved overall survival and decreased risk of thrombosis in polycythemia vera patients 4

Risk of Thrombosis

• The risk of thrombosis is higher in patients with polycythemia vera who require multiple phlebotomies per year 3
• Phlebotomy and hydroxyurea have been shown to reduce the risk of thrombosis in polycythemia vera patients 3, 4
• The European LeukemiaNet criteria for resistance/intolerance to hydroxyurea can help identify patients who may be at higher risk of thrombosis 3