From the Guidelines
A hematocrit level between 46.1-50.1% for a 37-year-old female over three years is elevated and requires immediate medical attention to reduce the risk of thrombosis, with a target hematocrit level of <45% as recommended by the most recent guidelines 1. This finding warrants medical evaluation to determine the underlying cause, which could be primary polycythemia, such as polycythemia vera, or secondary due to conditions like dehydration, living at high altitude, smoking, certain lung diseases, or sleep apnea. Key considerations for management include:
- Scheduling an appointment with a primary care physician for a complete blood count and additional testing
- Possible tests recommended by the doctor, including erythropoietin levels, JAK2 mutation testing, arterial blood gases, and possibly bone marrow examination
- Ensuring adequate hydration and avoiding smoking while waiting for the appointment
- Reporting any symptoms like headaches, dizziness, visual disturbances, or itching after bathing The elevated hematocrit increases blood viscosity and can raise the risk of blood clots, making prompt evaluation crucial. According to the CYTO-PV trial, targeting a hematocrit level <45% significantly reduced the composite primary endpoint of time until death from cardiovascular causes or major thrombotic events 1. Therefore, it is essential to follow the guidelines and aim for a hematocrit level below 45% to minimize the risk of thrombotic complications. No self-treatment should be initiated before professional assessment, as the appropriate management depends entirely on identifying the underlying cause. The use of low-dose aspirin, as assessed in the ECLAP trial, may also be considered to reduce the risk of thrombotic complications in patients with polycythemia vera 1.
From the Research
Hematocrit Levels and Polycythemia Vera
- A hematocrit level of 46.1-50.1 for the last three years in a 37-year-old female may indicate erythrocytosis, which is a characteristic of polycythemia vera (PV) 2, 3, 4, 5, 6.
- However, a hematocrit level below 59% may not accurately distinguish between true erythrocytosis and pseudoerythrocytosis due to plasma volume contraction 2.
- The presence of splenomegaly, leukocytosis, or thrombocytosis can help establish a diagnosis of PV, but in some cases, a direct measurement of red cell mass and plasma volume may be necessary 2.
Diagnostic Criteria for Polycythemia Vera
- The World Health Organization's major diagnostic criteria for PV include an elevated hemoglobin or hematocrit level, abnormal results on bone marrow biopsy, and presence of the Janus kinase 2 genetic mutation 3, 4, 5.
- A subnormal erythropoietin level can help differentiate PV from secondary causes of erythrocytosis, such as smoking or sleep apnea 3.
- A bone marrow biopsy is essential for diagnosis and baseline histomorphology, and both hematocrit and red cell counts should be controlled with phlebotomy and cytoreductive agents 6.
Treatment and Management of Polycythemia Vera
- Therapeutic phlebotomy to a hematocrit level of less than 45% and low-dose aspirin are recommended for all patients with PV to reduce the risk of thrombosis 3, 4, 5.
- Cytoreductive therapy with hydroxyurea or interferon may be necessary for patients at higher risk of thrombosis or with persistent symptoms 3, 4, 5, 6.
- Ruxolitinib, a Janus kinase inhibitor, can alleviate pruritus and decrease splenomegaly in patients who are intolerant of or resistant to hydroxyurea 4, 5.