Hematocrit normal range: what your hematocrit percentage means

Quick answer: hematocrit is the percentage of your blood made up of red blood cells. The hematocrit normal range on MedlinePlus is 37% to 48% for men and 34% to 43% for women; the MedlinePlus CBC article uses 40% to 55% for men and 36% to 48% for women, which shows how much labs differ. A result of 42 means 42% of your blood volume is red cells.

Track hematocrit at homeSiPhox reports a calculated hematocrit with hemoglobin on Longevity Essentials, Heart & Metabolic, GLP Optimization and Ultimate 360. $124 a test plus $25 shipping.

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Hematocrit normal range

MedlinePlus notes that normal hematocrit varies with sex, age, smoking and altitude, and that it rises for several weeks after moving to a higher altitude, as the body makes more red cells to carry oxygen in thinner air.

What hematocrit measures

Spin a tube of blood and it separates into packed red cells at the bottom and plasma on top. Hematocrit is the red cell share. Because it depends on both red cells and plasma volume, hematocrit rises when you lose water as well as when you make more red cells. It is reported in the complete blood count alongside hemoglobin, and the two usually move together.

What low hematocrit means

A low hematocrit usually means anemia. MedlinePlus lists:

• Bleeding, from injury or a chronic source such as heavy periods or the gut
• Deficiency of iron, folate, vitamin B12, vitamin B6 or copper
• Destruction of red cells (hemolysis), chronic kidney disease and chronic illness
• Bone marrow problems including leukemia, other cancers, medicine or radiation toxicity
• Pregnancy, malnutrition and too much water in the body

To find which one, doctors look at ferritin, iron, B12 and folate.

What high hematocrit means

MedlinePlus calls dehydration the most common cause of a high hematocrit. Others include cigarette smoking, low blood oxygen from lung disease such as pulmonary fibrosis, congenital heart disease, right-sided heart failure, a kidney tumor, living at altitude and polycythemia vera. A high hematocrit makes blood thicker, which is why it is watched closely in people taking testosterone.

Hematocrit and testosterone therapy

Testosterone stimulates red cell production. The Endocrine Society's 2018 guideline lists an elevated hematocrit as a reason not to start testosterone therapy and tells clinicians to measure hematocrit during treatment; its guideline materials call a hematocrit above 54% erythrocytosis and recommend checking it at baseline, 3 to 6 months after starting and then yearly. If hematocrit climbs past that level, the prescriber may lower the dose, pause treatment or arrange a blood draw. Our TRT blood test guide lists the full monitoring panel.

Worked example

A 47-year-old man starts testosterone with a hematocrit of 45%. At 4 months it is 50%, still inside the MedlinePlus CBC range of 40% to 55% but up 5 points. He tests again after a morning with plenty of water to rule out dehydration: 49%. At 12 months it is 53%, close to the 54% line, so his prescriber adjusts the plan. A quarterly home draw makes that trend visible between clinic visits, but decisions stay with the prescriber, who will use a venous CBC.

Getting a reliable hematocrit result

• Hydrate the day before. MedlinePlus calls dehydration the most common cause of a high hematocrit, so a dry morning can add a few points.
• Account for altitude and smoking. Hematocrit rises for several weeks at higher altitude, and smoking raises it too (MedlinePlus).
• Keep conditions the same between tests. Same time of day, same hydration, same lab. On testosterone therapy, note where you are in your dosing schedule so readings are comparable.
• Confirm before acting. A capillary or calculated hematocrit near 54% should be confirmed with a venous CBC before any change to therapy.

At-home tests that include hematocrit

Hematocrit is on four SiPhox panels: Longevity Essentials, Heart & Metabolic, Ultimate 360 and GLP Optimization. SiPhox labels it "HCT capillary (calc)": a calculated value from the capillary sample, not a spun or directly measured hematocrit. It is not on Thyroid Focus or Hormone Focus. The +$45 CBC add-on adds a capillary hematocrit and the full red cell indices.

Because capillary and calculated values can differ from a venous CBC, treat SiPhox's hematocrit as a trend line. SiPhox is a wellness service with no doctor review included. See our SiPhox review.

A note on home samples: SiPhox's partner lab tests capillary blood collected from the upper arm. SiPhox says its results show a 95% to 99% correlation with venous draws in its own quarterly comparisons against Labcorp and Quest, but it has not published a study of the EasyDraw device. If a result would change a treatment decision, confirm it with a venous test through your doctor.

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Everything on the four core panels plus iron studies, B12 and folate, GGT and PSA.

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Watch hematocrit between clinic visitsLongevity Essentials pairs hemoglobin and hematocrit with testosterone, estradiol, ApoB and HbA1c.

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