What It Measures
Hematocrit measures the proportion of red blood cells (erythrocytes) relative to the total volume of blood. It is expressed as a percentage — for example, a hematocrit of 42% means that 42% of the blood volume is made up of red blood cells, with the remainder being plasma, white blood cells, and platelets.
Hematocrit measures the percentage of your blood volume that is composed of red blood cells. It is a key indicator of oxygen-carrying capacity and overall blood health, commonly included in a complete blood count (CBC). Abnormal hematocrit levels can signal dehydration, anemia, bone marrow disorders, or chronic disease.
Current Value
What High Means
Elevated hematocrit (polycythemia) indicates an abnormally high concentration of red blood cells. This can result from dehydration (which concentrates the blood), chronic hypoxia (e.g., living at high altitude, smoking, COPD, or sleep apnea triggering increased erythropoietin production), polycythemia vera (a myeloproliferative neoplasm), testosterone replacement therapy, kidney tumors producing excess erythropoietin, or congenital heart disease. High hematocrit increases blood viscosity, raising the risk of blood clots, stroke, and heart attack.
Possible Symptoms
Headaches, dizziness, blurred vision, flushing or redness of the skin (plethora), itching (especially after warm showers), fatigue, shortness of breath, enlarged spleen, night sweats, joint pain, increased risk of blood clots (deep vein thrombosis, pulmonary embolism), chest pain
What Low Means
Low hematocrit (anemia) indicates a reduced proportion of red blood cells. Causes include iron deficiency, vitamin B12 or folate deficiency, chronic kidney disease (reduced erythropoietin), bone marrow disorders (aplastic anemia, leukemia, myelodysplastic syndromes), chronic inflammatory diseases, acute or chronic blood loss (GI bleeding, heavy menstruation), hemolytic anemias, and overhydration. Low hematocrit impairs oxygen delivery to tissues, causing fatigue and organ dysfunction.
Possible Symptoms
Fatigue, weakness, pale skin, shortness of breath (especially with exertion), dizziness or lightheadedness, rapid or irregular heartbeat, cold hands and feet, brittle nails, headaches, difficulty concentrating, chest pain, restless leg syndrome
Risk Factors
Polycythemia vera, chronic obstructive pulmonary disease (COPD), congenital heart disease, sleep apnea, iron deficiency anemia, chronic kidney disease, bone marrow failure, vitamin B12/folate deficiency, thalassemia, sickle cell disease, liver cirrhosis, hypothyroidism, testosterone replacement therapy, heavy menstrual bleeding, gastrointestinal bleeding, dehydration
Actionable Advice
Supplements
- •Iron (ferrous bisglycinate)
- •Vitamin B12 (methylcobalamin)
- •Folate (methylfolate)
- •Vitamin C (enhances iron absorption)
- •Copper
- •Vitamin B6 (pyridoxal-5-phosphate)
- •Vitamin A (retinol)
- •EPO-supportive nutrients (if kidney-related)
- •Chlorophyll-rich supplements (chlorella, spirulina)
Diet & Lifestyle
- •Address underlying causes — work with a physician to identify why hematocrit is abnormal
- •Stay well-hydrated (dehydration falsely elevates hematocrit)
- •Eat iron-rich foods (red meat, liver, spinach, lentils) if low; avoid excess iron if high
- •Include vitamin C-rich foods with iron sources to enhance absorption
- •Avoid smoking — carbon monoxide drives compensatory red blood cell production
- •Treat sleep apnea if present (CPAP can normalize erythropoietin levels)
- •Regular moderate exercise improves oxygen utilization and blood health
- •Limit alcohol intake — chronic alcohol use can suppress bone marrow
- •If on testosterone replacement therapy, monitor hematocrit regularly (target < 50%)
- •Consider therapeutic phlebotomy if hematocrit is persistently elevated (> 52%)
- •Ensure adequate B12 and folate intake, especially on plant-based diets
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Historical Trend
Related Biomarkers
Resources & Studies
All Readings
| Date | Value | Change |
|---|---|---|
| 2026-01-28 | 47.4 % | -2.0 |
| 2025-09-18 | 49.4 % | -2.6 |
| 2025-08-25 | 52 % | +4.1 |
| 2025-07-31 | 47.9 % | +5.6 |
| 2025-06-27 | 42.3 % | — |