Glossary term
Haemoglobin
Also known as: Hemoglobin, Hb, Hgb
Part of: Blood Test Results
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- 5 min read
- Last reviewed
- Last reviewed January 1970
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- Written in plain English
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- Reviewed by Medipher Editorial Team
The protein inside red blood cells that carries oxygen from your lungs to the rest of your body.
Medipher explains medical wording in plain English — it does not diagnose or replace a clinician. If this is a medical emergency, call your local emergency number immediately.
Simple visual explanation
What is this?
Haemoglobin is a special protein inside every red blood cell. It contains iron, which lets it grab oxygen in your lungs and release it wherever your body needs it — your muscles, brain, heart and every other organ.
When clinicians talk about your 'haemoglobin level', they mean how much of this protein is in a small sample of your blood. It is one of the most common measurements in medicine because it is a fast, reliable way to check that oxygen is being delivered around the body properly.
The value on your report is produced by an automated analyser that measures haemoglobin in grams per litre (g/L) or grams per decilitre (g/dL). Different labs use slightly different reference ranges, which is why your report always shows its own.
A haemoglobin result is a snapshot in time. It can shift with hydration, recent illness, pregnancy, altitude and diet, so clinicians usually look at it alongside other blood-count values such as MCV, red blood cells and ferritin.
Why is it important?
Doctors request haemoglobin as part of a Full Blood Count for almost every general health check, before surgery, during pregnancy and whenever symptoms such as tiredness, breathlessness, dizziness or pale skin need explaining.
A low haemoglobin is the main way anaemia is identified. A high haemoglobin can point to dehydration or, less commonly, other conditions that make the body produce extra red blood cells.
Trends matter more than any single number. A haemoglobin that has been stable for years is usually reassuring, even if it sits slightly outside the reference range, while a value that has been falling steadily is more useful clinically than a single low reading.
Where you'll see it: Full Blood Count (FBC) or Complete Blood Count (CBC) reports, usually shown as Hb or Hgb in g/L or g/dL.
How doctors use this result
Clinicians may use this result to:
- Screen for anaemia during routine check-ups, pregnancy and pre-operative assessments.
- Investigate symptoms such as fatigue, breathlessness, dizziness or pale skin.
- Monitor known conditions — kidney disease, chronic inflammation or ongoing blood loss.
- Track the response to treatment such as iron, B12 or folate replacement.
What's the normal range?
| Adult women (typical) | 120–150 g/L (12.0–15.0 g/dL) |
| Adult men (typical) | 130–170 g/L (13.0–17.0 g/dL) |
| Pregnancy | Slightly lower is expected, especially in the second trimester. |
Reference ranges vary between laboratories, and children and older adults have their own ranges. Always use the range printed on your own report.
A result a little above or below the printed range is very common and doesn't automatically mean something is wrong. Clinicians interpret haemoglobin alongside your age, sex, pregnancy status, symptoms and other blood values.
Normal ranges are guides, not verdicts. Interpretation depends on your age, sex, symptoms, medical history, medications and other investigations — which is why your clinician looks at the whole picture rather than a single value.
Common reasons it may be high
Dehydration
Less fluid in the blood makes haemoglobin look concentrated; the value often normalises once you're rehydrated.
Smoking
Carbon monoxide from tobacco reduces oxygen delivery, so the body slowly makes more haemoglobin to compensate.
High altitude
Thinner air means less oxygen per breath, so the body produces extra red blood cells over weeks.
Lung or heart conditions
Long-term low oxygen levels push the bone marrow to make more red cells.
Polycythaemia (uncommon)
A bone-marrow condition where too many red blood cells are produced; usually investigated further.
Common reasons it may be low
Iron deficiency
Without enough iron, the body can't build normal amounts of haemoglobin — the most common cause worldwide.
Vitamin B12 or folate deficiency
These vitamins are needed to make healthy red blood cells; low levels reduce production.
Blood loss
Heavy periods, gut bleeding or surgery all reduce circulating red cells and haemoglobin.
Pregnancy
Blood volume rises faster than red-cell production, naturally diluting haemoglobin.
Long-standing illness
Kidney disease, thyroid disease and chronic inflammation can slow red-cell production.
Some medications
Certain chemotherapy and other drugs temporarily reduce bone-marrow activity.
Does an abnormal result always mean something is wrong?
Not necessarily. A number that sits outside the printed range is a prompt for interpretation — not a diagnosis.
- A single result rarely gives the full picture — clinicians interpret it alongside your symptoms.
- Your medical history, medications and other blood tests all shape the meaning of one value.
- Small movements just outside the reference range are common and often not concerning.
- Repeat testing over time is frequently more useful than any single number.
What might happen next?
- A repeat blood test to confirm the result.
- Extra tests such as ferritin, B12 and folate to find the cause of a low result.
- A review of medications, diet, periods or gut symptoms.
- Referral to a specialist if the cause is unclear or the level is very low.
One result rarely tells the whole story. Clinicians look at your symptoms, medical history, medications and other tests together — and a single value that sits slightly outside the reference range is often normal for you. Repeat testing over time is frequently more useful than any one number. Medipher helps you understand what a result means in plain English, but it cannot diagnose medical conditions or replace advice from a doctor, nurse or pharmacist.
When should I speak to a healthcare professional?
Speak with your GP or another healthcare professional if:
- You've been asked to repeat the test.
- You're experiencing new or worsening symptoms.
- Your clinician has flagged the result as needing follow-up.
- You don't understand your results or feel unsure what to do next.
If you have severe symptoms — chest pain, severe breathlessness, fainting, heavy bleeding or feel very unwell — seek urgent help. If this is a medical emergency, call your local emergency number immediately. Medipher is designed to help explain medical information and is not an emergency service.
Frequently asked questions
Related blood tests
Terms clinicians often look at alongside Haemoglobin.
- Red Blood CellsThe cells in your blood that carry oxygen. They contain haemoglobin, which does the actual oxygen carrying.
- MCVThe average size of your red blood cells.
- AnaemiaA condition where you don't have enough healthy red blood cells or haemoglobin to carry oxygen around your body.
- FerritinA protein that stores iron in your body. Ferritin levels are used to estimate your total iron stores.
Related guides
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Sources
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- Next upRed Blood CellsThe cells in your blood that carry oxygen. They contain haemoglobin, which does the actual oxygen carrying.
- Next upMCVThe average size of your red blood cells.
- Next upAnaemiaA condition where you don't have enough healthy red blood cells or haemoglobin to carry oxygen around your body.
This glossary entry is general health information, not medical advice. Medipher explains medical wording in plain English and does not diagnose, provide treatment advice, or replace a GP, doctor, nurse or pharmacist. Always discuss your results with a qualified clinician.