Biomarker Glossary

Haemoglobin

Haemoglobin (Hb) is the iron containing protein in red blood cells that carries oxygen from the lungs to every tissue in your body. A haemoglobin blood test is the standard UK measure for anaemia and is a core component of any full blood count (FBC).

Also known as: Hb, Hgb

Haemoglobin is most informative when read alongside related markers like Ferritin and Iron. A single number rarely tells the whole story. If your reading sits outside the typical range, share the full report with your GP or healthcare professional before drawing conclusions.

What is Haemoglobin?

Haemoglobin gives blood its red colour and is responsible for carrying around 98 percent of the oxygen in your bloodstream. Each red blood cell contains around 270 million haemoglobin molecules.

Low haemoglobin (anaemia) means your blood cannot carry as much oxygen, causing fatigue, breathlessness and reduced exercise tolerance. High haemoglobin can reflect dehydration, high altitude exposure or, less commonly, blood disorders.

Haemoglobin is part of a full blood count (FBC) alongside red blood cell count, haematocrit, white cells and platelets. It is interpreted with iron studies, vitamin B12, folate and reticulocyte count to find the cause of anaemia.

Why test Haemoglobin?

  • To investigate symptoms of anaemia: fatigue, breathlessness, pale skin, dizziness.
  • To monitor known blood conditions.
  • Before surgery or pregnancy.
  • As part of a routine health screen.
  • If you donate blood regularly or have heavy menstrual bleeding.
To investigate symptoms of anaemia: fatigue, breathlessness, pale skin, dizziness.

Haemoglobin normal range (UK)

Result What it means
Men: 135 to 175 g/L Normal
Women: 115 to 155 g/L Normal
Pregnancy: above 110 g/L (first and third trimester) or above 105 (second trimester) Normal in pregnancy
Below the normal range Anaemia. Mild, moderate or severe depending on the value.
Above the normal range Polycythaemia or dehydration

UK NHS reference ranges. The cut off for anaemia is 130 g/L for men and 120 g/L for non pregnant women (World Health Organization).

About these ranges. The ranges above are typical UK clinical lab ranges aligned to NHS and Royal College of Pathologists guidance. Your Chxhealth report will show the specific reference range used by our partner lab, Randox, for each marker. Lab ranges vary slightly between providers and assays. Always interpret your results in the context of the range printed on your own report.

What causes high Haemoglobin?

  • Dehydration (most common cause of mildly raised Hb)
  • Living at high altitude
  • Smoking
  • Polycythaemia vera (a blood disorder)
  • Chronic lung or heart disease (the body makes more red cells to compensate for low oxygen)
  • Performance enhancing drugs (EPO, anabolic steroids)
  • Severe dehydration after burns, vomiting or diarrhoea

What causes low Haemoglobin?

  • Iron deficiency anaemia (the most common cause in the UK)
  • Vitamin B12 or folate deficiency
  • Chronic disease anaemia (chronic kidney disease, autoimmune disease, cancer)
  • Recent blood loss (heavy periods, gastrointestinal bleeding)
  • Bone marrow disorders
  • Haemolytic anaemia (red cells broken down too quickly)
  • Sickle cell disease and thalassaemia (inherited)
  • Pregnancy (dilutional)

Symptoms of high Haemoglobin

  • Headaches
  • Dizziness
  • Flushed skin
  • Fatigue paradoxically
  • Itching, particularly after a hot shower
  • Increased risk of blood clots in severe cases

Symptoms of low Haemoglobin

  • Fatigue and weakness
  • Shortness of breath, particularly with activity
  • Pale skin or nail beds
  • Dizziness or lightheadedness
  • Cold hands and feet
  • Rapid or irregular heartbeat
  • Hair shedding
  • Difficulty concentrating
  • Restless legs
  • Headaches

How is Haemoglobin tested?

Haemoglobin is measured as part of a full blood count (FBC), from a small blood sample. No fasting is required.

Stay well hydrated for 24 hours before the test. Significant dehydration can falsely raise Hb.

Best interpreted alongside iron studies, B12 and folate to find the cause of any abnormality.

Chxhealth samples are analysed by Randox, a UK laboratory accredited by UKAS. Results return in 3 to 5 working days.

How to support healthy Haemoglobin levels

  • Eat iron rich foods (red meat, liver, oily fish, lentils, beans, dark leafy greens).
  • Ensure adequate vitamin B12 (animal foods or a supplement if vegan or over 50).
  • Eat folate rich foods (leafy greens, beans, fortified cereals).
  • Address heavy menstrual bleeding or gut symptoms that may underlie anaemia.
  • Stay hydrated for accurate testing.
  • Stop smoking, which can falsely raise Hb and chronically irritates the lungs.

These are general lifestyle suggestions. Chxhealth is an information service. For personal medical advice, please speak to a healthcare professional.

Chxhealth panels that test Haemoglobin

15 Chxhealth biomarker panels include Haemoglobin. Each is analysed by Randox, a UK laboratory accredited by UKAS. Reports are delivered in 3 to 5 working days.

Haemoglobin FAQs

What is a normal haemoglobin level?

135 to 175 g/L for men and 115 to 155 g/L for women. The World Health Organization defines anaemia as below 130 g/L for men and 120 g/L for non pregnant women.

Can low haemoglobin cause fatigue?

Yes, and very commonly. Anaemia means less oxygen reaches your tissues, leading to tiredness, breathlessness and reduced exercise tolerance. Iron deficiency is the most common cause in the UK.

What is the difference between haemoglobin and haematocrit?

Haemoglobin measures the actual oxygen carrying protein in your blood. Haematocrit measures the percentage of your blood that is red blood cells. They usually move together but can differ in some conditions.

How quickly can haemoglobin recover from iron deficiency?

With consistent iron supplementation, haemoglobin typically rises by 10 to 20 g/L per month. Full recovery usually takes 2 to 4 months. Severe deficiency may need intravenous iron under medical supervision.

Can high haemoglobin be dangerous?

Yes, particularly when persistently high. It increases blood viscosity and the risk of blood clots, heart attack and stroke. Always investigate the cause: dehydration, smoking, lung disease or rare blood disorders.

Often tested with Haemoglobin

The biomarkers below are commonly investigated alongside Haemoglobin because they reveal connected aspects of the same physiological picture:

  • Ferritin: Iron stores deplete before haemoglobin drops.
  • Iron: Circulating iron supply for haemoglobin synthesis.
  • Vitamin B12: B12 deficiency causes its own pattern of anaemia.

Choose the right test for your goal

If you are reading about Haemoglobin because of a specific health goal, our buying guides walk you through which Chxhealth panels fit:

Sources and further reading

This page is informed by guidance from the NHS, NICE, Royal College of Pathologists and other UK authoritative bodies. For deeper detail or to verify the information, see:

About this page. Last reviewed: 13 May 2026. Next scheduled review: May 2027. This page has not yet been independently reviewed by a clinician. It is written from authoritative UK medical guidance (NHS, NICE, Royal College of Pathologists, peer-reviewed sources) but has not undergone formal clinical sign off.

Important. Chxhealth is a UK information service. We do not diagnose, treat or prescribe. The reference ranges and information on this page are general educational content and should not be used as a substitute for advice from a qualified healthcare professional. For any concerns about your health or results, please speak to your GP or another healthcare professional.