Haemoglobin Levels Explained: Low, Normal and High

Haemoglobin is the iron-rich protein inside your red blood cells. It carries oxygen from your lungs to the rest of your body. It is measured as part of a full blood count (FBC), one of the most common blood tests in the UK, and it is the main number doctors use to decide whether someone has anaemia.

This guide explains what low, normal and high haemoglobin results mean, the thresholds UK doctors use, the most common causes and when to speak to a GP. Reference ranges vary slightly between laboratories, so always read your result against the range printed on your own report.

Test it in Chiswick: our Full Blood Count blood test costs £59, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000.

Quick answer

In the UK, anaemia is usually defined as a haemoglobin below 130 g/L in men and below 120 g/L in women who are not pregnant. In pregnancy the threshold is 110 g/L, and 105 g/L is considered adequate in the second and third trimesters. Typical adult laboratory ranges are about 130 to 180 g/L for men and 115 to 165 g/L for women. A result above the range can be linked to dehydration, smoking or some medicines, and less often to a bone marrow condition. Your practitioner will look at the whole blood count, not one number alone.

What is haemoglobin?

Your body needs iron, vitamin B12 and folate to build new red cells, which is why a shortage of any of these can lower your haemoglobin.

UK laboratories report haemoglobin in grams per litre (g/L). Some older reports and overseas laboratories use grams per decilitre (g/dL). To convert, divide by ten: 130 g/L is the same as 13.0 g/dL.

Haemoglobin is reported alongside other red cell measurements, including the red cell count, haematocrit (the proportion of your blood made up of red cells) and mean cell volume (MCV, the average size of your red cells).

What your haemoglobin result means

• Low in men: below 130 g/L is the usual UK threshold for anaemia in men aged over 15.
• Low in women: below 120 g/L is the usual threshold for anaemia in women aged over 15 who are not pregnant.
• Pregnancy and after birth: below 110 g/L during pregnancy, with 105 g/L considered adequate in the second and third trimesters, and below 100 g/L after giving birth.
• Within range: typical adult laboratory ranges are about 130 to 180 g/L for men and about 115 to 165 g/L for women. Some laboratories use slightly different limits.
• High: above the upper limit on your report, often about 165 g/L for women and 180 g/L for men. Doctors usually look at the haematocrit too. NHS guidance for GPs flags a haematocrit above 0.52 in men or 0.48 in women for a repeat test.

You may notice that some laboratory ranges for women start at 115 g/L, while the anaemia threshold is 120 g/L. A result between the two is a borderline area where your practitioner will consider your symptoms, your iron levels and your other results before deciding whether anything needs doing.

How red cell size helps find the cause

A typical adult MCV is about 80 to 100 fL. When haemoglobin is low and the red cells are small (an MCV below 80), iron deficiency is the most common reason. When the cells are large (an MCV above 100), vitamin B12 or folate deficiency are among the possible causes.

Symptoms of low haemoglobin

Mild anaemia often causes no symptoms at all and is found on a routine blood test. When symptoms do appear, the NHS lists these as the most common:

• tiredness and lack of energy
• shortness of breath
• noticeable heartbeats (palpitations)
• pale skin
• headaches

Less common symptoms include ringing in the ears, a sore tongue, hair loss, spoon-shaped nails and restless legs.

Common causes of low haemoglobin

• Iron deficiency: the most common cause in the UK. Heavy periods and pregnancy are frequent reasons, often alongside a diet low in iron.
• Bleeding from the stomach or bowel: for example from regular use of anti-inflammatory painkillers such as ibuprofen or aspirin, stomach ulcers, inflammation of the bowel or gullet, or piles. Less commonly, bowel or stomach cancer can cause slow bleeding, which is why unexplained iron deficiency is always looked into.
• Vitamin B12 or folate deficiency: these vitamins are needed to make healthy red cells. Read our guides to vitamin B12 levels and folate levels.
• Inherited conditions: such as sickle cell disease and thalassaemia, which affect how haemoglobin is made.

Causes of high haemoglobin

A high haemoglobin or haematocrit means your blood contains a higher concentration of red cells than usual. The NHS describes several types:

• Apparent or relative: the number of red cells is normal but the liquid part of the blood is reduced. Dehydration, being overweight, smoking, heavy drinking and water tablets (diuretics) can all cause this.
• Secondary: the body makes more red cells in response to something else, such as long-term lung disease (for example COPD) or some kidney conditions. NHS guidance for GPs also lists testosterone, anabolic steroids and a group of diabetes medicines called SGLT2 inhibitors.
• Primary: a bone marrow condition called polycythaemia vera, which is rare and usually linked to a change in the JAK2 gene.

Symptoms can include headaches, blurred vision, red skin, dizziness and itching after a bath or shower.

What to do about your result

A haemoglobin result outside the range starts a conversation rather than giving a diagnosis. If your haemoglobin is low, the next step is usually to find out why. A ferritin test shows how much iron you have stored, and our guide to ferritin levels explains how to read it. Vitamin B12 and folate are often checked at the same time.

The NHS advises treating the underlying cause first, such as heavy periods or a stomach ulcer. If you are prescribed iron tablets, a course usually lasts about six months. Try not to start iron supplements before the cause is known.

If your haemoglobin is high, a repeat test when you are well hydrated is often the first step. Your GP may then review your medicines, smoking and lung health.

When to see your GP or get urgent help

See your GP if you have symptoms of anaemia, if your haemoglobin is below the range on your report, or if a high result is confirmed on a repeat test. Unexplained iron deficiency anaemia should always be investigated, especially in men and in women who no longer have periods.

Call 999 or go to A&E if you have:

• chest pain, or sudden or severe shortness of breath
• fainting or collapse
• vomiting blood, or black, tarry stools
• a painful, swollen leg together with breathlessness or coughing up blood, which can be signs of a blood clot
• signs of a stroke, such as a drooping face, weak arm or slurred speech

If you feel unwell and are not sure what to do, call NHS 111.

Who should consider a haemoglobin test

• People who feel tired all the time, breathless or lightheaded without a clear reason.
• Women with heavy periods, and anyone pregnant or planning a pregnancy.
• People following a restrictive, vegetarian or vegan diet.
• Men using testosterone or anabolic steroids, which can raise the red cell count.

Preparing for the test

A full blood count needs no special preparation and you do not need to fast. If you are having other tests from the same sample that do need fasting, follow the instructions you are given when you book. Tell us if you have recently been unwell, dehydrated or had a blood transfusion, as these can affect the result.

How often to retest

If you are being treated for anaemia, your GP may arrange repeat blood tests to check your levels are recovering. If a high haematocrit is found without urgent features, NHS guidance for GPs suggests repeating the test in about two months. If your result was within range and you feel well, there is no fixed schedule, and many people simply check it as part of a yearly health check.

Frequently asked questions

Is a haemoglobin of 125 low?

For a man, yes: 125 g/L is below the usual threshold of 130 g/L, so it counts as mild anaemia. For a woman who is not pregnant, 125 g/L is above the threshold of 120 g/L and is usually within range.

Is a haemoglobin of 115 normal for a woman?

It sits in a grey area. Some laboratory ranges for women start at 115 g/L, but the usual anaemia threshold for women who are not pregnant is 120 g/L. A ferritin test is often a useful next step to check your iron stores.

What haemoglobin level is dangerous?

There is no single number, as how you feel matters as much as the result. NHS guidance for GPs treats a haemoglobin below 80 g/L as one marker of severe anaemia. Any low result with chest pain, fainting or severe breathlessness needs urgent medical help.

Can I have low haemoglobin with normal ferritin?

Yes. Anaemia is not always caused by low iron. Vitamin B12 or folate deficiency, recent blood loss, long-term health conditions and inherited conditions can all lower haemoglobin while ferritin stays within range.

Can dehydration raise haemoglobin?

Yes. When you are dehydrated the liquid part of your blood is reduced, so your haemoglobin and haematocrit can look higher than they really are. A repeat test when you are well hydrated often settles the question.

Haemoglobin testing in Chiswick

We offer the Full Blood Count, which measures your haemoglobin alongside your red cells, white cells and platelets at Omnia Lifestyle, 8 to 9 Bedford Corner, The Avenue, Chiswick, London W4 1LZ. We are a short walk from Turnham Green station on the District line (Piccadilly line trains stop there early in the morning and late in the evening only), and buses 94, E3 and 272 stop nearby. Limited parking is available on request when you book. Your sample is taken at the clinic and analysed at the Randox accredited laboratory, and most results are ready within a few working days. You do not need a GP referral. A practitioner goes through your result with you in person, and a GP feedback report is available on request.

Find out more about our Full Blood Count, or check your iron stores at the same time with our Iron Status Check. You can also compare every blood test and price, or read our guides to ferritin levels and vitamin B12 levels.

This article is general information, not medical advice. Discuss your results with your GP or practitioner.