From the Guidelines
Isolated high hematocrit should be managed by targeting hematocrit levels to <45% to lower the risk of thrombosis, as evidenced by the CYTO-PV trial which showed a significant reduction in the composite primary endpoint of time until death from cardiovascular causes or major thrombotic events 1. The condition is characterized by an elevated percentage of red blood cells in the blood without other abnormalities. Initial steps should include confirming the finding with repeat testing and evaluating for dehydration, which can be addressed with increased fluid intake.
If hematocrit remains elevated, further workup should include:
- Complete blood count
- Serum erythropoietin levels
- JAK2 mutation testing to rule out polycythemia vera and other myeloproliferative disorders Secondary causes like smoking, chronic lung disease, sleep apnea, and high-altitude living should be investigated and addressed. Management depends on the underlying cause but may include therapeutic phlebotomy to maintain hematocrit below 45% in men and 42% in women if polycythemia vera is diagnosed. Aspirin 81-100mg daily may be recommended to reduce thrombotic risk in certain cases, as shown in the ECLAP trial which demonstrated a reduced risk of nonfatal myocardial infarction, nonfatal stroke, or death from cardiovascular causes 1.
Patients should be advised to stay well-hydrated, avoid smoking, and limit alcohol consumption. Elevated hematocrit increases blood viscosity and can lead to thrombotic complications including stroke, heart attack, and deep vein thrombosis, making proper diagnosis and management essential for preventing these serious outcomes 1.
From the Research
Isolated High Hematocrit
- Isolated high hematocrit is a condition where the hematocrit level is elevated, which can increase the risk of thrombosis and other complications.
- According to 2, elevated hematocrit is associated with an increased risk of thrombosis, and controlling hematocrit to <45% is a target associated with reduced rates of cardiovascular death and major thrombosis.
- The goal of therapy in patients with polycythemia vera, a condition characterized by isolated high hematocrit, is to reduce the risk of thrombosis by controlling hematocrit to <45% 3, 4, 5, 6.
- Therapeutic phlebotomy to maintain a hematocrit of less than 45% is a recommended treatment for patients with polycythemia vera 3, 5, 6.
- Low-dose aspirin is also recommended for patients with polycythemia vera to reduce the risk of thrombosis 3, 5, 6.
- Cytoreductive therapies, such as hydroxyurea or interferon, may be recommended for patients at high risk of thrombosis 2, 3, 5, 6.
Risk Factors
- Age ≥60 years and a history of thrombosis are important risk factors for thrombosis in patients with polycythemia vera 2, 3, 5.
- Elevated hematocrit and leukocytosis are also associated with an increased risk of thrombosis 2.
- The presence of the JAK2 gene variant can help distinguish polycythemia vera from secondary causes of erythrocytosis 3, 6.
Treatment
- Phlebotomy and low-dose aspirin are recommended for low-risk patients with polycythemia vera 2, 3.
- Cytoreductive agents, such as hydroxyurea or interferon, are recommended for high-risk patients with polycythemia vera 2, 3, 5, 6.
- Ruxolitinib may be considered for patients who are intolerant of or have an inadequate response to hydroxyurea 2, 3.