Type the hematocrit result from your blood test and pick who it is for. You see it against the range the NIH prints, the range MedlinePlus prints today, and — in pregnancy — the anemia line the NIH quotes from ACOG, with what the sources say moves the number. Your lab’s own range, and your doctor, have the last word.
40% is
Inside ODS’s range for women 40% = 0.4 L/L
40%: inside ODS’s 36–44% for women, and inside MedlinePlus’s current 34–43%.
That is inside the range NIH ODS prints for women. The range printed on your own lab report is the one your doctor will read it against.
What moves the number, in the sources’ words
- Normal hematocrit levels will vary, depending on your sex, age, whether or not you smoke, and the altitude where you live.
| Who | NIH ODS | MedlinePlus today |
|---|---|---|
| Women | 36–44% | 34–43% |
| Men | 41–50% | 37–48% |
| Pregnancy, 1st trimester | anemia under 33% (ACOG) | — |
| Pregnancy, 2nd trimester | anemia under 32% (ACOG) | — |
| Pregnancy, 3rd trimester | anemia under 33% (ACOG) | — |
| Newborns | — | 45–61% |
| Infants | — | 32–42% |
What a hematocrit can and cannot tell you. NIH ODS: “Hemoglobin and hematocrit tests are the most commonly used measures to screen patients for iron deficiency, even though they are neither sensitive nor specific.” MedlinePlus: “Normal value ranges vary slightly among different labs.”
This is not medical advice and it does not diagnose anything. It shows where a number sits against published ranges; what your result means for you depends on your lab, your other results, your history and your doctor.
NIH’s Office of Dietary Supplements: “Normal hematocrit values are approximately 41% to 50% in males and 36% to 44% in females.” MedlinePlus, the page ODS cites, now prints 37% to 48% for men and 34% to 43% for women. In pregnancy, ODS quotes ACOG’s anemia lines: under 33% in the first and third trimesters, under 32% in the second.
How to use it
Find “Hematocrit” (or “HCT”, sometimes “PCV”) on your complete blood count, type the number and pick who the test is for. A report prints it as a percentage, like 40, or as a fraction, like 0.40 L/L — pick the one that matches; switching converts the number you typed. You see where it sits against NIH ODS’s range and MedlinePlus’s current one (or ACOG’s line in pregnancy, or MedlinePlus’s ranges for babies), and what the sources say moves the number. Where the two ranges disagree, the page says so instead of choosing.
The ranges, and why there are two
NIH ODS (Iron fact sheet, updated September 4, 2025) prints its adult ranges with MedlinePlus as the reference. MedlinePlus’s Hematocrit page has since been revised (review date 2/27/2026): “Normal results vary, but in general they are: Male: 37% to 48% Female: 34% to 43%”, and “For babies, normal results are: Newborn: 45% to 61% Infant: 32% to 42%”, adding that “Normal value ranges vary slightly among different labs.” For pregnancy, ODS quotes ACOG, which recommends “evaluating those who have anemia (defined as hematocrit levels less than 33% in the first and third trimesters and less than 32% in the second trimester)”. Neither source prints an upper line in pregnancy or a range for children between infancy and adulthood, so this page does not invent one. The WHO’s 2024 guideline on anaemia sets hemoglobin cutoffs, not hematocrit ones — for those, see the Hemoglobin Level Checker.
The unit is a share of your blood. MedlinePlus: “For example, if your hematocrit test result is 42, it means that 42% of your blood is red blood cells, and the rest is made up of white blood cells, platelets, and blood plasma.” A report that prints 0.42 L/L is saying the same thing as a fraction.
| Result | Who | NIH ODS | MedlinePlus today |
|---|---|---|---|
| 33% | Woman | Under | Under |
| 35% | Woman | Under | Inside |
| 40% | Woman | Inside | Inside |
| 43.5% | Woman | Inside | Above |
| 46% | Woman | Above | Above |
| 39% | Man | Under | Inside |
| 45% | Man | Inside | Inside |
| 49% | Man | Inside | Above |
| 52% | Man | Above | Above |
What moves the number
MedlinePlus’s Hematocrit Test page: “Normal hematocrit levels will vary, depending on your sex, age, whether or not you smoke, and the altitude where you live.” On the high side, dehydration is “the most common cause of a high hematocrit”, and “Your hematocrit will increase for several weeks when you are at a higher altitude.” On the low side, “Pregnancy can cause a low hematocrit. That’s because your body has more fluid than usual during pregnancy, which decreases the percentage that’s made of red blood cells.” And: “If your results are not in the normal range, it doesn’t always mean you have a medical condition that needs treatment.”
MedlinePlus lists what a low hematocrit may be due to: Bleeding; Bone marrow being unable to produce new red blood cells. This may be due to leukemia, other cancers, medicine toxicity, radiation therapy, infection, or bone marrow disorders; Chronic illness; Chronic kidney disease; Destruction of red blood cells (hemolysis); Leukemia; Malnutrition; Pregnancy; Deficiency of copper, iron, folate, vitamin B12, or vitamin B6; Too much water in the body. And a high one: Bone marrow disease that causes abnormal increase in RBCs (polycythemia vera); Cigarette smoking; Dehydration (for example, from severe diarrhea); Failure of the right side of the heart (cor pulmonale); Kidney tumor (renal cell carcinoma); Low blood oxygen level (hypoxia); Problem with heart’s structure and function that is present at birth (congenital heart disease); Scarring or thickening of the lungs (pulmonary fibrosis). Which of these, if any, applies to you is your doctor’s question, not a list’s.
Worked examples
- 40% for a woman (the page’s example) is inside both NIH ODS’s 36–44% and MedlinePlus’s 34–43%.
- 35% for a woman is under ODS’s 36% but inside MedlinePlus’s 34–43% — where the two disagree, and the page says so.
- 0.49 L/L for a man is 49%: inside ODS’s 41–50%, above MedlinePlus’s 48%.
- 31% in the second trimester is under the 32% line ACOG uses to define anemia — a conversation with your doctor or midwife.
Common mistakes
- Reading the number without your lab’s range. Even the NIH and MedlinePlus print different ranges today; your report prints its own.
- Reading a normal hematocrit as “my iron is fine”. NIH ODS: “Hemoglobin and hematocrit tests are the most commonly used measures to screen patients for iron deficiency, even though they are neither sensitive nor specific.” ODS calls serum ferritin “a measure of the body’s iron stores” — see the Ferritin Level Checker.
- Forgetting how much you drank. MedlinePlus calls dehydration the most common cause of a high hematocrit.
- Using a non-pregnant range in pregnancy. Extra fluid lowers the percentage; ACOG’s line is the one ODS quotes.
Frequently asked questions
What are normal hematocrit levels?
NIH ODS: approximately 41% to 50% in males and 36% to 44% in females. MedlinePlus’s page today: 37% to 48% for men and 34% to 43% for women. Your lab’s own range is the one your doctor uses.
What is the hematocrit normal range for women?
36% to 44% (NIH ODS) or 34% to 43% (MedlinePlus today). In pregnancy, ODS quotes ACOG’s anemia line instead: under 33% in the first and third trimesters, under 32% in the second.
What is the hematocrit normal range for men?
41% to 50% (NIH ODS) or 37% to 48% (MedlinePlus today). The two overlap from 41% to 48%.
What does a high hematocrit mean?
That more of your blood’s volume is red cells than the range expects. MedlinePlus calls dehydration “the most common cause of a high hematocrit”, notes that altitude raises it for several weeks, and lists smoking among the causes. It is a conversation with your doctor, not a diagnosis.
What does a low hematocrit mean?
That less of your blood’s volume is red cells than the range expects. MedlinePlus lists bleeding, pregnancy and deficiencies of iron, folate and vitamin B12 among many possible reasons — and says a result outside the range “doesn’t always mean you have a medical condition that needs treatment”.
Is hematocrit the same as hemoglobin?
No. Hematocrit is the share of the blood’s volume that is red cells; hemoglobin is a protein inside them, measured in g/dL. NIH ODS names both as the common iron screening tests, and writes that iron deficiency anemia “is characterized by low hemoglobin concentrations and decreases in hematocrit”. The Hemoglobin Level Checker reads the other number.
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This is not medical advice, and nothing here diagnoses or treats anything. It shows where a number sits against published ranges; what it means for you is a conversation with your doctor, who knows your lab, your other results and your history. Some links on this site are affiliate links: I buy what I review at full price, and a commission never changes a verdict.