Hemoglobin (Hb): Normal Range, High & Low Causes
What Hemoglobin measures
Hemoglobin carries oxygen from your lungs to the rest of your body. Low hemoglobin is the main marker of anemia.
Hemoglobin reference ranges
| Category | Conventional units | SI units |
|---|---|---|
| Adult men | 13.5 – 17.5 g/dL | 135 – 175 g/L |
| Adult women | 12.0 – 15.5 g/dL | 120 – 155 g/L |
| Anemia (WHO): men | Below 13 g/dL | Below 130 g/L |
| Anemia (WHO): women, not pregnant | Below 12 g/dL | Below 120 g/L |
Levels differ with age, pregnancy and altitude. People living at high altitude normally run higher.
Need to convert units? Use the g/dL ↔ g/L converter.
Common causes of a high result
- Dehydration (relative rise)
- Smoking
- Living at high altitude
- Chronic lung or heart disease
- Polycythemia vera or other blood disorders
- Testosterone treatment
Common causes of a low result
- Iron deficiency (the most common cause)
- Vitamin B12 or folate deficiency
- Blood loss, including heavy periods
- Chronic disease or kidney disease
- Thalassemia or sickle cell disease
- Hemolytic anemia
How to prepare for the test
No fasting needed.
How often to retest
As advised. Low results are usually followed by iron, B12 and folate tests to find the cause.
Track Hemoglobin over time
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Get the appFrequently asked questions
What is a normal hemoglobin level?
About 13.5–17.5 g/dL for men and 12.0–15.5 g/dL for women.
What does low hemoglobin feel like?
Tiredness, breathlessness on exertion, paleness, dizziness and headaches are common, but mild anemia can cause no symptoms.
What should I do about low hemoglobin?
See your clinician to find the cause. Iron, B12 or folate supplements help only when those are the cause, so test before treating.
Related tests
Sources
This page is general education and was last updated 2026-10-30. It is not a substitute for medical advice. See our editorial approach.