Symptoms of Elevated Hematocrit
Elevated hematocrit causes hyperviscosity symptoms including headache, faintness, dizziness, fatigue, tinnitus, blurred vision, and tingling of fingers, toes, and lips, though these symptoms are unlikely when hematocrit is below 65% in patients with adequate iron stores. 1
Primary Hyperviscosity Symptoms
The classic constellation of hyperviscosity symptoms includes:
- Neurological symptoms: Headache, faintness, dizziness, poor concentration, and fatigue that interfere with daily activities 1
- Sensory disturbances: Tinnitus (ringing in ears), blurred vision, and paresthesias (tingling/numbness) of the fingers, toes, and lips 1
- Musculoskeletal complaints: Muscle pain and weakness 1
These symptoms are classified as moderate when they interfere with some activities, and severe when they interfere with most activities 1. Importantly, hyperviscosity symptoms are unlikely to occur in iron-replete patients with hematocrit below 65% 1.
Thrombotic and Vascular Complications
Beyond direct hyperviscosity effects, elevated hematocrit significantly increases thrombotic risk:
- Cardiovascular events: Elevated hematocrit is independently associated with increased long-term cardiovascular mortality, particularly when combined with inflammation 2
- Venous thromboembolism: Men with hematocrit ≥46% have a 1.5-fold increased risk of total venous thromboembolism and a 2.4-fold increased risk of unprovoked venous thromboembolism 3
- Cerebrovascular accidents: These may result from thromboembolic events, paradoxical emboli, or rheological factors related to increased blood viscosity 1
- Stroke complications: Higher hematocrit values are associated with reduced reperfusion and greater infarct size in acute ischemic stroke 4
Bleeding Manifestations
Paradoxically, elevated hematocrit can cause both thrombosis and bleeding:
- Minor bleeding: Spontaneous dental bleeding, epistaxis (nosebleeds), easy bruising, and menorrhagia are usually self-limiting 1
- Major bleeding: Hemoptysis (coughing up blood) is the most common major bleeding event, occurring in up to 100% of patients with Eisenmenger syndrome, representing intrapulmonary hemorrhage 1
Cardiovascular and Hemodynamic Effects
The increased blood viscosity from elevated hematocrit creates measurable physiologic changes:
- Blood pressure effects: A 10.99% increase in hematocrit produces approximately 20% increase in blood viscosity, which can decrease blood flow rate by 16.67% or require compensatory blood pressure increase of 20% 5
- Reduced tissue perfusion: Chronic hypoxemia, increased blood viscosity, and endothelial dysfunction affect microcirculation and organ function 1
Physical Examination Findings
In patients with secondary erythrocytosis from chronic hypoxemia:
- Central cyanosis: Results from increased quantity of reduced hemoglobin (>5 g/100 mL blood) 1
- Clubbing: Digital clubbing of fingers and toes 1
- Scoliosis: Frequently present in cyanotic patients 1
Critical Threshold Considerations
The severity of symptoms correlates with the degree of hematocrit elevation, with the critical threshold being 65% 1. Below this level in iron-replete patients, hyperviscosity symptoms are uncommon. However, iron deficiency can cause symptoms at lower hematocrit levels because iron-deficient red cells are less deformable and have reduced oxygen-carrying capacity 1.
Important Clinical Pitfall
A common mistake is attributing all symptoms to hyperviscosity when iron deficiency may be the actual culprit. Iron deficiency can mimic hyperviscosity symptoms and paradoxically increases stroke risk despite lower hematocrit 6. Microcytosis from iron deficiency was identified as the strongest independent predictor for cerebrovascular events, not the elevated hematocrit itself 1.