Hematocrit

Percentage of blood volume occupied by red blood cells

20/22Providers

Complete Blood Category

Men:38-50%, Women:Reference

Widely Available

20 of 22 providers

Reference Range

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

Range Type	Level	Significance
Optimal	Men: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.
Borderline	Men: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.

Standard lab range: Men:38-50%, Women:35-45%

How to Optimize Hematocrit

1. Same as Hemoglobin—Treat Anemia

Iron supplementation:Ferrous sulfate 325 mg 2-3x daily. Hematocrit increases 3-6% per month

B12/Folate replacement:As per hemoglobin guidelines. Hematocrit normalizes in 1-3 months

ESAs for chronic disease:Target hematocrit 30-36% (hemoglobin 10-12 g/dL)

Transfusion:Each unit packed RBCs increases hematocrit by ~3%. Transfuse if <21-24% with symptoms

2. Manage Polycythemia - Target Hematocrit <45%

Phlebotomy:Remove 250-500 mL blood every 2-7 days until hematocrit <45% (men) or <42% (women). The CYTO-PV trial established <45% as the target

Aspirin:81 mg daily reduces thrombosis in polycythemia vera by 30-40%

Hydroxyurea:If high thrombosis risk (age >60, prior clot). Reduces hematocrit and platelet count

Hydration:Ensure 2-3 liters fluids daily. Dehydration worsens viscosity effects

3. Correct Hydration Status

If elevated hematocrit with normal hemoglobin:Likely dehydration. Increase fluids to 2-3 liters daily and retest

Calculate plasma volume:In dehydration, both hemoglobin and hematocrit rise proportionally. In polycythemia, RBC mass is truly increased

Monitor urine:Dark urine suggests dehydration. Aim for pale yellow urine

IV fluids:If severe dehydration, may need 1-2 liters IV saline before accurate hematocrit assessment

4. Pregnancy and Dilutional Anemia

Expected drop:Hematocrit falls 5-7% in pregnancy due to 40-50% plasma volume expansion (physiologic anemia of pregnancy)

True anemia threshold:Hematocrit <33% (hemoglobin <11 g/dL) in pregnancy indicates iron deficiency

Iron supplementation:30-60 mg elemental iron daily throughout pregnancy. Increase to 120 mg if anemic

Recheck:Monthly hematocrit in pregnancy, more frequent if anemic

5. Altitude Adaptation

Physiologic increase:Hematocrit rises 1-2% for every 1000m elevation above sea level. At 3000m (10,000 ft), hematocrit may reach 50-55%

Chronic mountain sickness:Excessive polycythemia (hematocrit >60%) at altitude impairs oxygen delivery due to hyperviscosity

Treatment:Descent to lower altitude, phlebotomy if symptomatic, acetazolamide to reduce EPO drive

Athletes:Altitude training increases hematocrit 3-5% over 3-4 weeks, enhancing endurance performance for weeks after descent

Symptoms of Abnormal Hematocrit

Low Hematocrit

Low hematocrit symptoms identical to anemia:
Fatigue, weakness, shortness of breath
Pale skin, dizziness, rapid heartbeat
Cold extremities, headaches

High Hematocrit

High hematocrit (>52%) symptoms:
Headaches, dizziness, blurred vision
Facial redness (plethora), itching
Thrombosis risk:DVT, PE, stroke, MI

Causes of Abnormal Hematocrit

Low Levels

Same causes as low hemoglobin/RBC:
Blood loss, iron deficiency, B12/folate deficiency
Chronic disease, bone marrow disorders
Hemolysis, medications
Overhydration (dilutional)

High Levels

Polycythemia vera, secondary polycythemia (hypoxia, tumors)
Dehydration (most common acute cause)
Testosterone use, high altitude living
Smoking (chronic mild elevation)

When to Retest

After treatment:Hematocrit should increase 3-6% per month with iron/B12 therapy
After phlebotomy:Check hematocrit 1 week after each phlebotomy session. Continue until <45%
Dehydration:Retest after 24 hours of adequate hydration. Should normalize if dehydration was cause
Pregnancy:Monthly checks. Hematocrit falls progressively until delivery, then normalizes within weeks postpartum
Polycythemia:Monitor every 1-3 months. Maintain hematocrit <45% to minimize thrombosis risk

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.

Source:Marchioli R, et al. Cardiovascular events and intensity of treatment in polycythemia vera. N Engl J Med. 2013;368(1):22-33.

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.

Source:Pearson TC, et al. Rheological factors in the pathogenesis of arterial disease in polycythemia vera. J R Soc Med. 1978;71(11):813-818.

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.

Source:Bothwell TH. Iron requirements in pregnancy and strategies to meet them. Am J Clin Nutr. 2000;72(1 Suppl):257S-264S.

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+
Life Extension	✓	$486	40+
Everlywell	✓	$468	83
Mito Health	✓	$349	100+
InsideTracker	✓	$680	54
Function Health	✓	$365	100+
Marek Health Base	✓	$250	65
Marek Health Comprehensive	✓	$495	70+
Marek Health Complete	✓	$895	100+
Marek Health Executive	✓	$1950	150+
Blueprint	—	$399	100+
Quest Health	—	$Varies	75+
Empirical Health	✓	$190	100+
Oura Health Panels	✓	$99	50
SiPhox Health	—	$125	60
Hims Labs Base	✓	$199	50
Hims Labs Advanced	✓	$499	120+
Healthspan	✓	$4188	80+
Vitality Blueprint Standard	✓	$375	85
Vitality Blueprint Elite	✓	$700	129

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Frequently Asked Questions

What does Hematocrit test for?

Hematocrit is a complete blood count (cbc) biomarker. Percentage of blood volume occupied by red blood cells The normal reference range is Men:38-50%, Women:35-45%.

Which providers include Hematocrit?

20 of 22 providers include this test:Superpower, Blueprint, Mito Health, WHOOP and others.

How often should I test Hematocrit?

For most people, testing 2-4 times per year is recommended to establish baseline levels and track trends. Consult your healthcare provider for personalized recommendations.

What is the optimal range?

The standard reference range is Men:38-50%, Women:35-45%. Many functional medicine practitioners recommend tighter optimal ranges for peak health. Your ideal range may vary based on age, sex, and health goals.

Why is Hematocrit important?

Indicates blood's oxygen-carrying capacity. Low values suggest anemia;high values may indicate dehydration or lung disease. Used to diagnose and monitor blood disorders.

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.