What happens if my hematocrit (Hct) is too high?

High Hematocrit: Risks and Management

Elevated hematocrit significantly increases your risk of thrombotic events and should be maintained below 45% to reduce cardiovascular morbidity and mortality. 1

Understanding Hematocrit and Its Risks

Hematocrit (Hct) is the percentage of blood volume occupied by red blood cells. When hematocrit is too high, it causes:

• Increased blood viscosity - Blood becomes thicker and flows less efficiently
• Hyperviscosity syndrome - Can lead to symptoms like headache, dizziness, and visual disturbances
• Thrombotic complications - Higher risk of blood clots in arteries and veins

Specific Cardiovascular Risks

High hematocrit significantly increases the risk of:

• Stroke
• Myocardial infarction (heart attack)
• Deep vein thrombosis
• Pulmonary embolism

The CYTO-PV trial conclusively demonstrated that maintaining hematocrit below 45% significantly reduces the risk of cardiovascular events compared to higher levels (45-50%) 1. Patients with hematocrit levels above 45% had a 3.91 times higher risk of cardiovascular events and death.

Causes of High Hematocrit

High hematocrit can result from:

1. Primary polycythemia (Polycythemia Vera) - A myeloproliferative neoplasm with abnormal bone marrow production of red cells
2. Secondary polycythemia - Physiological response to hypoxemia from:
   • Chronic lung disease
   • Congenital heart disease
   • High altitude
   • Sleep apnea
3. Relative polycythemia - Due to decreased plasma volume (dehydration)
4. Testosterone therapy - Can stimulate erythropoiesis 1

Management of High Hematocrit

Immediate Management

For symptomatic high hematocrit:

• Phlebotomy - The cornerstone of emergency treatment for very high hematocrit with symptoms of hyperviscosity 1
• Hydration - First-line therapy for suspected hyperviscosity symptoms 1

Long-term Management

For primary polycythemia (Polycythemia Vera):

• Target hematocrit < 45% - This threshold has been proven to reduce thrombotic events 1
• Low-dose aspirin - Reduces risk of cardiovascular events 1
• Cytoreductive therapy - For high-risk patients (age >60 years or history of thrombosis) 1

For secondary polycythemia:

• Treat underlying cause when possible
• Judicious phlebotomy - May be appropriate in some cases, but routine phlebotomy is not supported by data 1
• Avoid iron deficiency - Iron deficiency can compromise oxygen transport without lowering viscosity 1

Special Considerations

Polycythemia in Congenital Heart Disease

In patients with cyanotic congenital heart disease:

• Secondary erythrocytosis is a physiological response to hypoxemia
• Phlebotomy should be performed only when symptoms persist after adequate hydration 1
• Target hematocrit may be higher (55-60%) in certain conditions like COPD or cyanotic heart disease 1

Testosterone Therapy

For patients on testosterone replacement:

• Monitor hematocrit regularly
• Risk of erythrocytosis is higher with injectable testosterone (43.8%) compared to transdermal preparations (15.4%) 1
• Consider dose reduction, withholding testosterone, or therapeutic phlebotomy if erythrocytosis develops 1

Warning Signs Requiring Medical Attention

Seek immediate medical attention for symptoms of hyperviscosity:

• Headache
• Visual disturbances
• Dizziness
• Fatigue
• Chest pain
• Shortness of breath
• Confusion
• Numbness or weakness in limbs

Remember that high hematocrit represents a significant risk factor for thrombotic events and should be managed appropriately based on the underlying cause and individual risk factors.