The short answer
Hematocrit is the share of your blood made up of red blood cells. It’s the number to watch if you take testosterone, which raises it: guidelines say to act at 54%.2,3
Check your result
Type the number from your report. It stays on this page.
- Low Under 34.0
- Normal 34.0 to 46.6
- Above the lab range 46.7 to 48.0
- High 48.1 or more
- Low Under 37.5
- Normal 37.5 to 48.0
- Normal, but high 48.1 to 51.0
- Above the lab range 51.1 to 53.9
- Very high 54.0 or more
Enter your result to see what it means and what to do next.
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For men, green stops at 48.0%, below the top of Labcorp’s range, because guidelines draw lines at 48% for starting testosterone and 49% for polycythemia vera.1,2 The 54% line is where guidelines say testosterone needs to change.2,3 The bar isn’t to scale.
Normal hematocrit
Your share of red cells is in the usual range, and below the lines guidelines use for too many red cells.1,2
Nothing to worry about.
- 1 If you take testosterone or plan to, keep checking it, 3 to 6 months after starting and then every year.2
- 2 If you smoke or have sleep apnea, recheck it with your next blood count. Both can push it up.3
- 3 Check your hemoglobin too. Anemia is judged on hemoglobin, and it can be under WHO’s cutoff, 12.0 g/dL for women or 13.0 for men, even when hematocrit is in range.8
Below the lab’s range
Less of your blood is made up of red cells than usual. Anemia is diagnosed on hemoglobin, so read that number on the same report next. Low iron is the most common cause of anemia.8
How soon to act depends on your hemoglobin, which the hemoglobin guide grades from mild to severe. Go the same day if you’re short of breath at rest, have chest pain or have black or bloody stools.
- 1 Check your hemoglobin against the anemia cutoffs on our hemoglobin guide.
- 2 Check ferritin and iron levels to see whether low iron is the cause.8
A little above the lab’s range
This is just above Labcorp’s range for women, but not above 48%, the line used to diagnose polycythemia vera.1 Smoking, sleep apnea, lung disease, living at altitude and testosterone can all push hematocrit up.3
Not urgent. Worth a recheck.
- 1 Repeat the CBC in a few weeks to see whether it stays high.
- 2 If you smoke, snore heavily or take testosterone, mention it to a clinician.3
Above the polycythemia vera line
Above 48%, a woman’s hematocrit meets the first criterion for polycythemia vera, a bone marrow condition that makes too many red cells. A diagnosis also needs a change in the JAK2 gene, plus either a bone marrow biopsy or a low level of the hormone erythropoietin.1 Other causes, such as smoking, sleep apnea and lung disease, need ruling out too.3
Not an emergency on its own. See a clinician in the next few weeks.
- 1 Repeat the CBC to confirm it.
- 2 If it stays high, ask about a JAK2 gene test and an erythropoietin level.1
Normal on your report, but above a guideline line
Labcorp’s range for men goes up to 51.0%, so this won’t be flagged. But the Endocrine Society lists a hematocrit above 48% as a moderate to high risk of harm from starting testosterone, and the AUA says to consider holding off above 50% until the cause is found.2,3 Above 49%, it also meets the first criterion for polycythemia vera.1
Not urgent. If you already take testosterone, you’re below the 54% line where guidelines say to act.2,3
- 1 If you’re thinking of starting testosterone, raise this result first. It may change the decision.2,3
- 2 If you already take testosterone, keep up your checks, at 3 to 6 months and then every year.2
- 3 If you don’t, repeat the CBC in a few weeks. If it stays above 49%, ask about smoking, sleep apnea and a JAK2 gene test.1,3
Above the lab’s range
Your hematocrit is above Labcorp’s range for men, and above the polycythemia vera line.1 Testosterone, smoking, sleep apnea, lung disease and living at altitude can all cause it, and so can polycythemia vera.1,3
Not an emergency. See a clinician in the next few weeks.
- 1 If you take testosterone, you’re close to the 54% line. Ask whether your dose or form should change. Injections raise hematocrit more than gels.2,3
- 2 If you don’t, ask about the cause, including sleep apnea, and about a JAK2 gene test.1,6
- 3 If you’re thinking of starting testosterone, guidelines advise waiting until the cause is known.2,3
Very high: the line where testosterone needs to change
The AUA says a hematocrit of 54% or more on testosterone needs action, starting with a lower dose if your testosterone level is high. The Endocrine Society says to stop testosterone above 54% until hematocrit falls to a safe level, check for sleep apnea and low oxygen, then restart at a lower dose.2,3 Off testosterone, a hematocrit this high needs its cause found.1,3
See a clinician within days. Get emergency care for sudden shortness of breath or a painful, swollen, warm leg, which can be signs of a blood clot.4
- 1 If you take testosterone, contact the clinician who prescribes it this week. Guidelines say to lower the dose or pause it.2,3
- 2 Ask whether removing some blood (a phlebotomy) makes sense for you.2
- 3 Get checked for sleep apnea.2
- 4 If you don’t take testosterone, ask about a JAK2 gene test and an erythropoietin level.1
What is a normal hematocrit level?
Labcorp calls 34.0% to 46.6% normal for women and 37.5% to 51.0% for men. For men, the guideline lines for polycythemia vera and for testosterone sit inside that range, so a result can look normal on your report and still matter:1,2,3
Normal hematocrit
Your share of red cells is in the usual range, and below the lines guidelines use for too many red cells.1,2
Nothing to worry about.
- 1 If you take testosterone or plan to, keep checking it, 3 to 6 months after starting and then every year.2
- 2 If you smoke or have sleep apnea, recheck it with your next blood count. Both can push it up.3
- 3 Check your hemoglobin too. Anemia is judged on hemoglobin, and it can be under WHO’s cutoff, 12.0 g/dL for women or 13.0 for men, even when hematocrit is in range.8
Below the lab’s range
Less of your blood is made up of red cells than usual. Anemia is diagnosed on hemoglobin, so read that number on the same report next. Low iron is the most common cause of anemia.8
How soon to act depends on your hemoglobin, which the hemoglobin guide grades from mild to severe. Go the same day if you’re short of breath at rest, have chest pain or have black or bloody stools.
- 1 Check your hemoglobin against the anemia cutoffs on our hemoglobin guide.
- 2 Check ferritin and iron levels to see whether low iron is the cause.8
A little above the lab’s range
This is just above Labcorp’s range for women, but not above 48%, the line used to diagnose polycythemia vera.1 Smoking, sleep apnea, lung disease, living at altitude and testosterone can all push hematocrit up.3
Not urgent. Worth a recheck.
- 1 Repeat the CBC in a few weeks to see whether it stays high.
- 2 If you smoke, snore heavily or take testosterone, mention it to a clinician.3
Above the polycythemia vera line
Above 48%, a woman’s hematocrit meets the first criterion for polycythemia vera, a bone marrow condition that makes too many red cells. A diagnosis also needs a change in the JAK2 gene, plus either a bone marrow biopsy or a low level of the hormone erythropoietin.1 Other causes, such as smoking, sleep apnea and lung disease, need ruling out too.3
Not an emergency on its own. See a clinician in the next few weeks.
- 1 Repeat the CBC to confirm it.
- 2 If it stays high, ask about a JAK2 gene test and an erythropoietin level.1
Normal on your report, but above a guideline line
Labcorp’s range for men goes up to 51.0%, so this won’t be flagged. But the Endocrine Society lists a hematocrit above 48% as a moderate to high risk of harm from starting testosterone, and the AUA says to consider holding off above 50% until the cause is found.2,3 Above 49%, it also meets the first criterion for polycythemia vera.1
Not urgent. If you already take testosterone, you’re below the 54% line where guidelines say to act.2,3
- 1 If you’re thinking of starting testosterone, raise this result first. It may change the decision.2,3
- 2 If you already take testosterone, keep up your checks, at 3 to 6 months and then every year.2
- 3 If you don’t, repeat the CBC in a few weeks. If it stays above 49%, ask about smoking, sleep apnea and a JAK2 gene test.1,3
Above the lab’s range
Your hematocrit is above Labcorp’s range for men, and above the polycythemia vera line.1 Testosterone, smoking, sleep apnea, lung disease and living at altitude can all cause it, and so can polycythemia vera.1,3
Not an emergency. See a clinician in the next few weeks.
- 1 If you take testosterone, you’re close to the 54% line. Ask whether your dose or form should change. Injections raise hematocrit more than gels.2,3
- 2 If you don’t, ask about the cause, including sleep apnea, and about a JAK2 gene test.1,6
- 3 If you’re thinking of starting testosterone, guidelines advise waiting until the cause is known.2,3
Very high: the line where testosterone needs to change
The AUA says a hematocrit of 54% or more on testosterone needs action, starting with a lower dose if your testosterone level is high. The Endocrine Society says to stop testosterone above 54% until hematocrit falls to a safe level, check for sleep apnea and low oxygen, then restart at a lower dose.2,3 Off testosterone, a hematocrit this high needs its cause found.1,3
See a clinician within days. Get emergency care for sudden shortness of breath or a painful, swollen, warm leg, which can be signs of a blood clot.4
- 1 If you take testosterone, contact the clinician who prescribes it this week. Guidelines say to lower the dose or pause it.2,3
- 2 Ask whether removing some blood (a phlebotomy) makes sense for you.2
- 3 Get checked for sleep apnea.2
- 4 If you don’t take testosterone, ask about a JAK2 gene test and an erythropoietin level.1
What is hematocrit?
If you spun a tube of your blood, the red cells would sink to the bottom. Hematocrit is how much of the tube they fill, as a percentage.
Hematocrit rises and falls with hemoglobin, the oxygen-carrying protein inside red cells, because both track how many red cells you have. Anemia is diagnosed on hemoglobin, so for a low result, that’s the guide to read.8 This one is mostly about the other end: a hematocrit that’s too high.
What causes high hematocrit?
Anything that makes your body produce more red cells can raise it. Causes include:
- Testosterone treatment, especially injections2,3
- Smoking3
- Sleep apnea and lung disease such as COPD, which lower your oxygen. Studies find too many red cells in about 2% to 8% of people with sleep apnea.3,6
- Living at high altitude3
- SGLT2 inhibitors, drugs for diabetes, heart failure and kidney disease whose names end in -gliflozin. In trials they raised hematocrit by about 2.4 percentage points on average, and the authors say it’s unclear whether that matters.7
- Polycythemia vera, a bone marrow condition linked to changes in the JAK2 gene, and some tumors1,3
How does testosterone affect hematocrit?
Testosterone drives red cell production.3 In trials, it raised hemoglobin by about 1.2 g/dL on average compared with a placebo.3 Injections raise it more than gels, and the rise is bigger in older men.2 In one series, 19% of men on injections went above a hematocrit of 52%, against 5% on gels.3
That’s why both US guidelines ask for a hematocrit before you start and while you’re on it, and draw these lines:2,3
| Endocrine Society | American Urological Association | |
|---|---|---|
| Before starting | Above 48% (50% at high altitude) is a moderate to high risk of harm from starting testosterone | Above 50%, consider holding off until the cause is found |
| On testosterone | Above 54%, stop until it falls, check for sleep apnea and low oxygen, then restart at a lower dose | 54% or more needs action, starting with a lower dose if your testosterone level is high |
| When to check | Before starting, at 3 to 6 months, then every year | Before starting, then every 6 to 12 months |
The FDA label for AndroGel, a testosterone gel, asks for the same checks: before starting, at 3 to 6 months, then every year.4
TRAVERSE, a large trial of testosterone gel in men aged 45 to 80 with low testosterone and heart disease or a high risk of it, showed both sides. Among men who started out anemic, 41% were no longer anemic at six months on testosterone, against 27.5% on a placebo. But six men had to stop because their hematocrit went above 54%, even on the lowest dose.5
How to lower a high hematocrit
- Changing your testosterone dose
When hematocrit runs too high and so does your testosterone level, a lower dose is the AUA’s first step. Above 54%, the Endocrine Society says to pause it until hematocrit falls, then restart lower.2,3
- How much it helps
- A lot
- How sure we are
- Very sure
- Switching from injections to a gel
Gels raise hematocrit less than injections do.2
- How much it helps
- Some
- How sure we are
- Fairly sure
- Removing blood
A phlebotomy is an option on testosterone. In polycythemia vera, phlebotomy and medicine keep hematocrit under 45%.2,6
- How much it helps
- A lot
- How sure we are
- Very sure
- Treating sleep apnea
In people with sleep apnea, long-term CPAP has been shown to bring down a high red cell count.6
- How much it helps
- Some
- How sure we are
- Fairly sure
-
- How much it helps
- A little
- How sure we are
- Fairly sure
What works depends on the cause, so find that first. If you take an SGLT2 inhibitor, the rise is small, so don’t stop it without talking to the clinician who prescribes it.7
Who should get a hematocrit test?
Hematocrit is part of every complete blood count. It’s worth checking if any of these apply to you:
- You’re about to start testosterone, or take it.2,3,4
- You have sleep apnea or a lung disease such as COPD.6
- You smoke, or live at high altitude.3
- You’ve had a high result before and want to see whether it’s come down.
How to get a hematocrit test, and what it costs
It comes from the complete blood count, which costs $3.75 through Picardo.
Complete blood count
The test this number comes from.
- Results in 2 to 3 days, in the app
- Physician follow-up if you want one
- Free Labcorp draw, or $75 at home
- No other fees. HSA and FSA eligible.
It’s also part of the Base Core Annual – Men, Base Core Annual – Women, Heart Health, Brain Health Screening, Pregnancy, Postpartum, Fertility, Thyroid & Autoimmunity and Celiac / GI panels, if you’d rather test more at once.
Already have a result? Ask Picardo about itQuestions people ask
Is a high hematocrit dangerous?
It can be. The FDA label for AndroGel, a testosterone gel, warns that more red cells may raise the risk of blood clots.4 In polycythemia vera, keeping hematocrit under 45% is part of preventing clots.6 On testosterone, the risk is less clear. In TRAVERSE, among men who started out anemic, a rising hematocrit on testosterone wasn’t linked to major heart events or blood clots.5
What’s the difference between hematocrit and hemoglobin?
Hematocrit is how much of your blood is red cells, as a percentage. Hemoglobin is how much of the oxygen-carrying protein inside them you have. Both track your red cells, so guidelines give cutoffs for either.1,9 Anemia is diagnosed on hemoglobin.8
Does donating blood lower your hematocrit?
Yes. Removing blood lowers it, which is why phlebotomy is one of the options when testosterone pushes it too high.2 To donate, the FDA requires a hematocrit of at least 39% for men and 38% for women, or a high enough hemoglobin.9
Why does testosterone raise hematocrit?
Testosterone stimulates the bone marrow to make red cells. A rise in hemoglobin and hematocrit is the most common side effect of testosterone treatment. It usually climbs for the first six months, then levels off.3
Often checked alongside
Test details
- Labcorp test
- Complete Blood Count (CBC) With Differential, Reflex to Peripheral Smear Review, 005009
- LOINC
- 4544-3
- Sample
- Blood
- Fasting
- Not needed
- Typical lab range
- 34.0% to 46.6% (women); 37.5% to 51.0% (men)
- Units
- %
Sources
- 1 Arber DA, Orazi A, Hasserjian RP, et al. International Consensus Classification of myeloid neoplasms and acute leukemias: integrating morphologic, clinical, and genomic data. Blood. 2022;140(11):1200–1228. doi.org/10.1182/blood.2022015850
- 2 Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744. doi.org/10.1210/jc.2018-00229
- 3 Mulhall JP, Trost LW, Brannigan RE, et al. Evaluation and management of testosterone deficiency: AUA guideline. J Urol. 2018;200(2):423–432. doi.org/10.1016/j.juro.2018.03.115
- 4 AndroGel (testosterone gel) 1.62%: prescribing information. Revised July 2025. DailyMed, US National Library of Medicine. dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=f4e8d29b-8707-4d47-e053-2a95a90aecee
- 5 Pencina KM, Travison TG, Artz AS, et al. Efficacy of testosterone replacement therapy in correcting anemia in men with hypogonadism: a randomized clinical trial. JAMA Netw Open. 2023;6(10):e2340030. doi.org/10.1001/jamanetworkopen.2023.40030
- 6 McMullin MFF, Mead AJ, Ali S, et al. A guideline for the management of specific situations in polycythaemia vera and secondary erythrocytosis: a British Society for Haematology guideline. Br J Haematol. 2019;184(2):161–175. doi.org/10.1111/bjh.15647
- 7 Yang Y, Yang C, Wang Y, et al. Sodium-glucose cotransporter 2 inhibitor use and levels of hemoglobin, markers of iron metabolism, and erythropoiesis: a systematic review and meta-analysis of randomized clinical trials. JAMA. Published online October 24, 2026. doi.org/10.1001/jama.2026.19921
- 8 World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. Geneva: WHO; 2024. www.who.int/publications/i/item/9789240088542
- 9 US Food and Drug Administration. General donor eligibility requirements. 21 CFR 630.10. Electronic Code of Federal Regulations. Accessed October 28, 2026. www.ecfr.gov/current/title-21/chapter-I/subchapter-F/part-630/subpart-B/section-630.10
Updated 4 Nov 2026.
This is general health information, not medical advice: talk to your clinician about your results and before changing any treatment.