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What is being tested?

This test measures the amount of haemoglobin (a protein found in red blood cells) in your blood and is a good indication of your blood's ability to carry oxygen throughout your body. Haemoglobin carries oxygen to cells from the lungs. If your haemoglobin levels are low, you have anaemia, a condition in which your body is not getting enough oxygen, causing fatigue and weakness.

How is it used?

The test is used to:

  • detect and measure the severity of anaemia (too few red blood cells) or polycythaemia (too many red blood cells)
  • monitor the response to treatment, and
  • help make decisions about blood transfusions.

When is it requested?

Haemoglobin measurement is part of the full blood count (FBC) (which is requested for many different reasons) and before operations when a blood transfusion is anticipated. The test is also repeated in patients who have ongoing bleeding problems.

What does the result mean?

Normal values in an adult male are approximately 135 to 175 grams per litre, and an adult female, 115 to 165 grams per litre of blood but are influenced by the age, sex and ethnic origin of the person. Above-normal haemoglobin levels may be the result of:

  • dehydration
  • excess production of red blood cells in the bone marrow
  • severe lung disease, or
  • several other conditions.

Below-normal haemoglobin levels may be the result of:

  • iron deficiency
  • blood loss through trauma or during surgery
  • inherited haemoglobin defects
  • bone marrow failure
  • cirrhosis of the liver (during which the liver becomes scarred)
  • bleeding
  • vitamin and mineral deficiencies
  • kidney disease, 
  • other chronic illnesses
  • cancers that affect the bone marrow.

Is there anything else I should know?

Haemoglobin decreases slightly during normal pregnancy.

Haemoglobin levels peak around 8 a.m. and are lowest around 8 p.m. each day.

eavy smokers have higher haemoglobin levels than non-smokers.

Living in high altitudes increases haemoglobin values. This is your body's response to the decreased oxygen available at these heights.

Haemoglobin levels are slightly lower in older men and women and in children.

Common questions

  • Does exercise affect haemoglobin levels?

No, except that dehydration can temporarily increase haemoglobin levels.

  • How do you treat abnormally low haemoglobin levels?

Treatment depends upon the cause. Some types of anaemia are treated with iron, folic acid or vitamin B12 or B6 supplements.

  • Is anyone at greater risk of abnormal haemoglobin levels?

Women of childbearing age may have temporary decreases during menstrual periods and pregnancy.

  • Are there warning signs for abnormally low haemoglobin levels?

Some warning signs are fatigue, fainting, pallor (loss of normal skin colour) and shortness of breath.

  • Can a healthy diet and good nutrition help keep optimal haemoglobin levels?

A healthy diet containing vegetables and foods high in iron can be beneficial.

More information

RCPA Manual: Haemoglobin

Last Updated: Thursday, 1st June 2023

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