What can cause a slight elevation in hematocrit (HCT)?

From the Guidelines

A slight elevation in hematocrit (HCT) can be caused by several factors, including dehydration, high altitude, polycythemia vera, chronic obstructive pulmonary disease (COPD), congenital heart disease, smoking, and certain medications or substances like erythropoietin, anabolic steroids, and testosterone replacement therapy. These conditions can lead to increased red blood cell production or reduced plasma volume, resulting in a higher concentration of red blood cells in the blood.

• Dehydration is the most common cause, as reduced plasma volume concentrates red blood cells, and can be addressed by increasing fluid intake 1.
• Living at high altitude can increase HCT as the body produces more red blood cells to compensate for lower oxygen levels, which is a physiological response to hypoxia 1.
• Certain medical conditions like polycythemia vera, COPD, and congenital heart disease can elevate HCT by triggering increased red blood cell production, often as a response to chronic hypoxia or other pathological stimuli 1.
• Smoking stimulates red blood cell production through carbon monoxide exposure, which can lead to an increase in HCT 1.
• Some medications and substances can raise HCT, including erythropoietin, anabolic steroids, and testosterone replacement therapy, by stimulating erythropoiesis or increasing red blood cell production 1.
• Stress or intense exercise may cause temporary elevations due to fluid shifts and splenic contraction, which can lead to a transient increase in HCT 1. It's essential to note that what constitutes a "slight" elevation varies by laboratory reference ranges, age, sex, and individual baseline values, and the management of elevated HCT should be tailored to the underlying cause, with consideration of the potential risks and benefits of treatment 1.

From the Research

Causes of Slight Elevation in Hematocrit (HCT)

• Polycythemia vera (PV), a myeloproliferative neoplasm characterized by an increased red blood cell mass and increased risk of thrombosis, can cause a slight elevation in HCT 2, 3, 4.
• Erythrocytosis, or an increase in red blood cell mass, can also lead to an elevated HCT 2, 3, 4.
• Dehydration or plasma volume contraction can cause a relative increase in HCT 2.
• Other conditions such as sleep apnea, tobacco smoking, and chronic hypoxia can also lead to an increase in HCT 2, 3, 4.
• Some patients with essential thrombocythemia (ET) may also experience an elevation in HCT, although this is less common than in PV 3, 4.

Risk Factors for Thrombosis in Patients with Elevated HCT

• Age >60 years 2, 3, 4
• History of thrombosis 2, 3, 4
• Presence of JAK2 mutation 2, 3, 4
• Cardiovascular risk factors 4
• Extreme thrombocytosis, which can lead to acquired von Willebrand syndrome (AvWS) and increased risk of bleeding 4

Treatment and Management of Elevated HCT

• Phlebotomy to maintain a hematocrit level <45% 2, 3, 4
• Low-dose aspirin therapy 2, 3, 4
• Cytoreductive therapy with hydroxyurea or interferon for high-risk patients 2, 3, 4
• Ruxolitinib, a Janus kinase inhibitor, for patients who are intolerant of or resistant to hydroxyurea 5