01 / Reference ranges
What counts as normal
Normal vs optimal
The WHO cutoffs are the 5th percentile of healthy populations: they define anemia, not an optimal zone. Values modestly above the cutoff are normal. WHO adjusts readings downward for smoking and altitude, both of which raise hemoglobin; a persistently high value is a clinical conversation, not a target, and this page's sources do not cover its workup.
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02 / Why it matters
What the number tells you
Anemia is one of the most common lab findings in the world, and hemoglobin is how it is defined: below 13.0 g/dL (130 g/L) in men and below 12.0 g/dL (120 g/L) in non-pregnant women, per the WHO 2024 guideline. The severity grades change the urgency: mild anemia is usually an outpatient iron question; severe anemia is an urgent evaluation. The cause matters more than the number, and iron deficiency (check ferritin) is the most common one.
03 / In practice
Testing and what moves it
When it is tested
- On any complete blood count: routine physicals, fatigue evaluations, pre-operative checks.
- With heavy menstrual bleeding, gastrointestinal symptoms, or a vegetarian or vegan diet plus symptoms.
- A low result leads to ferritin, B12 and sometimes kidney testing to find the cause.
What raises it
- Smoking and living at altitude: WHO's 2024 guideline publishes adjustments for both (for example, subtract 8 g/L at 1,000 to 1,499 m, and 3 to 6 g/L for smokers by cigarettes per day).
- Dehydration raises the concentration without adding red cells.
What lowers it
- Iron deficiency (blood loss, low intake, poor absorption), B12 or folate deficiency, chronic kidney disease, chronic inflammation, blood disorders.
- Pregnancy lowers it physiologically; pregnancy cutoffs differ by trimester.
04 / Related
Read next
Frequently asked questions
What hemoglobin level means anemia?
Below 13.0 g/dL (130 g/L) in adult men and below 12.0 g/dL (120 g/L) in non-pregnant women, per the WHO 2024 guideline. Pregnancy uses different, trimester-specific cutoffs.
What should I test after a low hemoglobin?
Usually ferritin first, because iron deficiency is the most common cause; then B12 and, depending on the picture, kidney function and stool testing for blood loss. Treating anemia without finding its cause misses the point of the test.
Is high hemoglobin good?
No; the WHO cutoffs mark anemia, not a ladder to climb. WHO's guideline adjusts readings downward for smoking and altitude, both of which raise hemoglobin. A persistently high value belongs with a clinician; this page's sources do not cover its workup.