Hematocrit
Percentage of blood volume occupied by red blood cells
20 of 22 providers
Complete Blood Count (CBC)
Men:38-50%, Women:35-45%
What is Hematocrit?
Hematocrit (Hct) is the percentage of blood volume occupied by red blood cells. Normal hematocrit is 38-50% in men and 35-45% in women. If your hematocrit is 45%, it means that 45% of your blood volume consists of red blood cells, while the remaining 55% is plasma (the liquid component).
Hematocrit is directly related to hemoglobin and RBC count—it is essentially a mathematical derivative of these values. The relationship is:Hematocrit ≈ Hemoglobin × 3 (e.g., hemoglobin 15 g/dL ≈ hematocrit 45%). Hematocrit reflects blood viscosity and oxygen-carrying capacity. Higher hematocrit means thicker blood, which can impair circulation if excessive.
Hematocrit is affected by hydration status more than hemoglobin or RBC count. Dehydration concentrates RBCs, falsely elevating hematocrit, while overhydration dilutes RBCs, lowering hematocrit. This makes hematocrit useful for assessing volume status. In clinical practice, hemoglobin is preferred over hematocrit for diagnosis and management because it directly measures oxygen-carrying capacity.
Why Hematocrit Reflects Blood Thickness and Volume Status
- Blood viscosity indicator:Hematocrit >50% significantly increases blood thickness, impairing microvascular flow and increasing clot risk
- Hydration assessment:More sensitive to dehydration than hemoglobin. Sudden hematocrit rise suggests volume depletion
- Polycythemia management:Target hematocrit <45% in polycythemia vera reduces thrombosis risk by 50%
- Altitude physiology:Increases 2-3% for every 1000m elevation above sea level as normal adaptation
- Pregnancy monitoring:Falls in pregnancy due to plasma volume expansion (dilutional effect). Low hematocrit helps identify iron deficiency
- Transfusion guide:Each unit of packed RBCs increases hematocrit by ~3%
Optimal vs Standard Ranges
OptimalMen:42-48%, Women:38-43%▼
- Ideal range balancing oxygen delivery with blood fluidity
- Provides adequate oxygen without excessive viscosity
- Supports optimal cardiovascular function and tissue perfusion
BorderlineMen:36-42% or 48-52%, Women:33-38% or 43-48%▼
- Low-normal may indicate mild anemia or hemodilution
- High-normal may indicate mild polycythemia or dehydration
- Check hemoglobin, hydration status
- Retest after proper hydration
Anemia<36% (men), <33% (women)▼
- Indicates anemia
- Severity:Mild 30-36%, Moderate 24-30%, Severe <24%
- Investigate cause with iron studies, B12, folate, reticulocyte count
- Transfusion typically not needed unless <21% with symptoms
Polycythemia>52% (men), >48% (women)▼
- Elevated hematocrit increases blood viscosity and thrombosis risk exponentially above 50%
- Requires investigation for polycythemia vera, secondary polycythemia, or dehydration
- Urgent phlebotomy if >60% or symptomatic
Scientific Evidence
Hematocrit <45% Target in Polycythemia Vera
The CYTO-PV trial randomized polycythemia vera patients to hematocrit target <45% vs <50%. The <45% group had 50% lower rate of cardiovascular death and major thrombosis. This established hematocrit <45% as the treatment target for polycythemia vera.
Blood Viscosity and Hematocrit
Blood viscosity increases linearly with hematocrit up to 45%, then exponentially above 50%. Hematocrit of 60% doubles blood viscosity compared to 40%. This impairs microvascular flow, reduces oxygen delivery despite high oxygen content, and dramatically increases thrombosis risk.
Dilutional Anemia of Pregnancy
Plasma volume increases 40-50% in pregnancy while RBC mass increases only 20-30%, causing dilutional drop in hematocrit of 5-7%. This "physiologic anemia"is normal. True anemia (hematocrit <33% or hemoglobin <11 g/dL) indicates iron deficiency requiring supplementation.
Hematocrit and Dehydration
Acute dehydration causes hemoconcentration, increasing hematocrit 1-2% for every 2% loss of body weight. This makes hematocrit useful for assessing hydration status in acute illness. However, chronic dehydration does not significantly elevate hematocrit as compensatory mechanisms maintain plasma volume.
Source:Popowski LA, et al. Blood and urinary measures of hydration status during progressive acute dehydration. Med Sci Sports Exerc. 2001;33(5):747-753.
Altitude and Hematocrit
Hematocrit increases ~1% for every 1000m above sea level as physiologic adaptation to reduced oxygen. Long-term residents at 4000m have hematocrit 50-55%. However, excessive polycythemia (>60%) indicates chronic mountain sickness with impaired oxygen delivery due to hyperviscosity.
Source:León-Velarde F, et al. Chronic mountain sickness. Respir Physiol Neurobiol. 2007;158(2-3):151-165.
Which Providers Test Hematocrit?
Full Provider Comparison
| Provider | Includes | Annual Cost | Biomarkers |
|---|---|---|---|
 Superpower | ✓ | $199 | 100+ (150 with ratios) |
 WHOOP Advanced Labs | ✓ | $349 | 65 |
 Labcorp OnDemand | ✓ | $398 | 30+ |
| ✓ | $486 | 40+ | |
| ✓ | $444 | 288 | |
| ✓ | $349 | 100+ | |
| ✓ | $761 | 54 | |
 Function Health | ✓ | $365 | 160+ |
| ✓ | $250 | 65 | |
| ✓ | $495 | 70+ | |
| ✓ | $895 | 100+ | |
| ✓ | $1950 | 150+ | |
| ✓ | $375 | 80+ | |
| — | $Varies | 75+ | |
| ✓ | $190 | 100+ | |
| ✓ | $99 | 50 | |
| — | $124 | 60 | |
| ✓ | $199 | 50 | |
| ✓ | $499 | 120+ | |
| ✓ | $4188 | 70-80+ | |
| ✓ | $375 | 85 | |
| ✓ | $700 | 128 |
Frequently Asked Questions
What is Hematocrit?
Percentage of blood volume occupied by red blood cells
What is the optimal range for Hematocrit?
The standard reference range for Hematocrit is Men:38-50%, Women:35-45%. Optimal ranges may differ based on individual health goals and expert recommendations.
Which blood test providers include Hematocrit?
20 out of 22 blood testing providers include Hematocrit in their panels. This biomarker is widely available across major providers.
What category does Hematocrit fall under?
Hematocrit is categorized under Complete Blood Count (CBC). This category includes biomarkers that help assess related aspects of health and wellness.
Medical Disclaimer
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.
Last reviewed:2026-02-20