Hematocrit
The share of your blood made up of red blood cells, shown as a percent. It usually moves together with hemoglobin.
AI-verified against cited sources. Awaiting expert reviewAlso called HCT, Hct, PCVLOINC 4544-3
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The usual range for Hematocrit depends on sex. Choose female or male above to see where you stand.
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What it is
Hematocrit is the percent of your blood volume taken up by red blood cells. The rest is mostly plasma, the liquid part of blood. Most labs get it from an automated analyzer as part of a complete blood count (CBC), and a spun-tube version is sometimes used. Some reports show it as a fraction, such as 0.42 instead of 42%.
Why it matters
Hematocrit helps show whether you have fewer red blood cells than expected (anemia) or more than expected (erythrocytosis). It also reflects how thick, or concentrated, your blood is, so it is tracked during some treatments such as testosterone therapy. It is read together with hemoglobin and the red cell count.
If it’s low
A low hematocrit means red blood cells make up a smaller share of your blood than expected. It usually goes along with a low hemoglobin (anemia). Pregnancy lowers it too, because extra fluid dilutes the blood.
Common causes
- Low iron or blood loss, including heavy periods
- Low vitamin B12 or folate
- Pregnancy, because blood volume rises
- Long-term conditions such as kidney disease or inflammation
- Extra fluid in the blood, such as after IV fluids
- Inherited blood conditions or, less often, bone marrow problems
What can help
- Ask which tests could find the cause, such as iron studies, vitamin B12 or folate
- Eat iron-rich foods such as beans, lentils, leafy greens, meat and fortified cereals
- Mention heavy periods, black stools or recent blood donation to your clinician
If it’s high
A high hematocrit often means your blood is more concentrated than usual, most commonly because of dehydration. It can also mean the body is making extra red blood cells in response to low oxygen, smoking or certain treatments. A clinician can tell which applies to you.
Common causes
- Dehydration, the most common cause
- Smoking, which raises carbon monoxide and prompts extra red cell production
- Living at high altitude
- Testosterone therapy and some other hormone products
- Conditions that lower oxygen levels, such as sleep apnea, long-term lung disease or some heart conditions present from birth
- Some medicines, including SGLT2 inhibitors
- Less often, polycythemia vera or a tumor that makes erythropoietin
What can help
- Ask whether hydration could explain the result and whether to repeat the test
- Tell your clinician if you smoke, use testosterone, live at altitude or have sleep problems
- If you use testosterone, ask which hematocrit level your prescriber wants to keep an eye on
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
The usual range depends on sex and age. Choose women or men to see the one that applies.
- Men, 13+37.5–51 %
Sources: Labcorp, Mayo Clinic Laboratories, ARUP Laboratories, Te Whatu Ora Health New Zealand, Waikato, StatPearls (NCBI Bookshelf)
- Women, 13+34–46.6 %
Sources: Labcorp, Mayo Clinic Laboratories, ARUP Laboratories, Te Whatu Ora Health New Zealand, Waikato, StatPearls (NCBI Bookshelf)
See Hematocrit by age and sex, with the U.S. survey numbers where they exist.
CDC anemia cutoffs in pregnancy (first trimester)
- Below the anemia cutoffbelow 33 %
- At or above the cutoff33 and above %
CDC anemia cutoffs in pregnancy (second trimester)
- Below the anemia cutoffbelow 32 %
- At or above the cutoff32 and above %
CDC anemia cutoffs in pregnancy (third trimester)
- Below the anemia cutoffbelow 33 %
- At or above the cutoff33 and above %
If this applies to you
Hematocrit means a little more for some people. Open the one that fits you.
Strength training
Hematocrit is the share of blood made of red cells. Testosterone and anabolic steroids raise hemoglobin and hematocrit in a dose-related way, and a high count is a common side effect.
On gender-affirming hormones
Testosterone raises red blood cells, so WPATH recommends checking hematocrit at the start, about every 3 months in the first year, then once or twice a year. A rise into the usual range for cisgender men is expected.
On testosterone therapy
Testosterone increases red blood cell mass, so hematocrit is a key safety test. The Endocrine Society suggests checking it before starting, at 3 to 6 months, then yearly. It treats a hematocrit above 54% as a reason for the clinician to review treatment, including checking for causes such as low oxygen levels or sleep apnea.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Hematocrit by age and sex: every percentile as a table, with a download.
What can affect your result
- Sex and age: higher in men than in women after puberty; children's values are lower and rise through the teen years
- Pregnancy: extra fluid dilutes the blood. The CDC uses 33% (first and third trimesters) and 32% (second trimester) as anemia cutoffs
- Altitude and smoking both raise hematocrit
- Hydration and posture: dehydration and standing before the draw raise it, and one small study found about 7% higher values standing than lying down
- Method: automated, calculated and spun results can differ slightly
- Cold agglutinins can distort automated results; a spun hematocrit stays reliable
- Recent blood donation, a transfusion or IV fluids
- Standing before the draw raises hematocrit compared with sitting or lying down (about 7% higher standing than lying down in one small study).
- Dehydration or a long tourniquet time can concentrate the blood and push the result up.
- Cold agglutinins (red cells clumping in cold blood) can distort automated hematocrit; a spun hematocrit stays reliable.
- Recent blood donation, a transfusion or IV fluids change the result.
- Automated, calculated and spun hematocrit can differ slightly because some plasma stays trapped between cells in a spun tube.
Any time of day. When you compare results over time, try to keep your posture and hydration similar. Red blood cells live about 120 days, so changes usually show over weeks to months. Dehydration or IV fluids can change it within hours.
When to talk to a clinician
If you have chest pain, trouble breathing or fainting, call 911 or your local emergency number. Labcorp's critical limits for hematocrit are below 18.1% and above 64.4%, levels where labs call the ordering clinician right away. If you take testosterone, your prescriber will usually track hematocrit, and the Endocrine Society guideline names 54% as a level that calls for a closer look at treatment. A result that stays outside your lab's range is worth raising at your next visit.
Questions you could ask
- How does my hematocrit compare with my earlier results?
- Does pregnancy, altitude or smoking change how I should read it?
- Could dehydration, smoking, altitude or any of my medicines explain this result?
- If I am on testosterone therapy, how often should my hematocrit be checked?
- What might be causing my hematocrit to be low?
- Should we check iron, vitamin B12 or folate, and when should we recheck?
Questions people ask
How are hematocrit and hemoglobin related?
Both reflect your red cells, so they rise and fall together. When red cells are a normal size, hematocrit is roughly three times the hemoglobin in g/dL, so 14 g/dL goes with about 42%. If the two do not line up, the lab may recheck the sample or look at your red cell indices.
My report shows 0.42 instead of 42. Is that the same thing?
Yes. Some countries report hematocrit as a fraction in L/L instead of a percent. Multiply the fraction by 100 to get the percent, so 0.42 L/L is 42%.
Can dehydration make my hematocrit look high?
Yes. When you are low on fluid, the liquid part of your blood shrinks, so red cells make up a bigger share. MedlinePlus lists dehydration as the most common cause of a high hematocrit. If your result is high, ask whether a repeat test makes sense.
Why is hematocrit lower in pregnancy?
Blood volume grows more than the red cell count does, so the red cells are more diluted. The CDC uses 33% in the first and third trimesters and 32% in the second as the points below which anemia is considered.
Why does my clinician check hematocrit on testosterone therapy?
Testosterone can raise red cell production in some people, and a higher hematocrit makes blood thicker. The Endocrine Society guideline suggests checking it before starting, at 3 to 6 months and then yearly, and reviewing treatment if it goes above 54%. Your prescriber decides what is right for you.
Show the science and sources
Units
- 1 % = 1 %
- 1 % = 0.01 L/L
Open the Hematocrit unit converter
Is a change real?
Hematocrit naturally varies about 2.71% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 8% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation estimates of 20 haematological parameters (Coskun A et al., EFLM WG-BV).
For clinicians and researchers
Hematocrit is the volume fraction of red cells in whole blood. The reference method is the spun microhematocrit, where a small amount of plasma stays trapped between the cells, so spun values run a little higher than analyzer values. Analyzers derive it either by calculation (red cell count x MCV / 10) or from summed red cell pulse heights, depending on the platform, which is why LOINC has separate codes for automated count, calculation and centrifugation. MCHC is hemoglobin divided by hematocrit, and because MCHC normally sits near 33 g/dL (ARUP adult intervals span 31.2-35.2 g/dL across both sexes), hematocrit is roughly three times the hemoglobin, so a mismatch can point to a measurement problem such as cold agglutinins. Labcorp's intervals (men 37.5-51.0%, women 34.0-46.6%) are lab specific, and StatPearls quotes 40-54% and 36-48%. The WHO 2016 major criterion for polycythemia vera is a hemoglobin above 16.5 g/dL or hematocrit above 49% in men (16.0 g/dL or 48% in women), alongside other findings (Tefferi 2021). The Endocrine Society (2018) advises measuring hematocrit at baseline, at 3 to 6 months and then yearly in men on testosterone therapy, and holding therapy if it exceeds 54%; a baseline above 48% (50% at altitude) is a relative contraindication. SGLT2 inhibitors raise hematocrit through hemoconcentration and higher erythropoietin.
LOINC 4544-3 (primary), 20570-8, 4545-0, 71833-8. Specimen: whole-blood.
Sources
- Critical (Panic) Values, with adult reference intervals (document DX_TL_811850, January 2024), Labcorp (2024)
- Pediatric Testing Reference Ranges (CBC With Differential/Platelet, test 005009), Labcorp (2022)
- CBC - Overview: Complete Blood Cell Count (CBC) with Differential, Blood, Mayo Clinic Laboratories
- CBC with Platelet Count and Automated Differential (test 0040003), Hotline effective March 1, 2021, ARUP Laboratories (2021)
- CBC reference intervals (procedure HEM-2597.01, effective 14 November 2024), Te Whatu Ora Health New Zealand, Waikato (2024)
- Hematocrit, StatPearls (NCBI Bookshelf)
- ACOG Practice Bulletin No. 233: Anemia in Pregnancy, American College of Obstetricians and Gynecologists (2021)
- Hematocrit Test, MedlinePlus (National Library of Medicine)
- Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2018)
- Patient posture for blood collection by venipuncture: recall for standardization after 28 years, Revista Brasileira de Hematologia e Hemoterapia (2017)
- When the CBC Cannot Be Trusted, The Blood Project
- Recommendations to Prevent and Control Iron Deficiency in the United States (MMWR Recommendations and Reports 47, RR-3), Centers for Disease Control and Prevention (1998)
- Polycythemia vera: historical oversights, diagnostic details, and therapeutic views, Leukemia (2021)
- Hemoglobin, Wikipedia
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.