Haemoglobin Test- Understand the Test

Also Known As

Formal Name

Haemoglobin

This article was last reviewed on

3 July 2023.

This article waslast modified on 3 July 2023.

At a Glance

Why Get Tested?

If you have anaemia (too few red blood cells) or polycythaemia (too many red blood cells), to assess its severity, and to monitor response to treatment

When To Get Tested?

As part of a full blood count (FBC), which may be requested for a variety of reasons

Sample Required?

A blood sample collected from a vein in your arm or by a finger-prick (children and adults) or heel-prick (newborns)

Test Preparation Needed?

Ideally you should be reasonably hydrated when having a haemoglobin test or the result may be inaccurately high

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

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 from the lungs to the cells. If your haemoglobin levels are low, you have anaemia, a condition in which your body is not getting enough oxygen, causing tiredness, fatigue and weakness. If your haemoglobin levels are high, this usually means you have too many red cells which is called polycythaemia. Polycythaemia, when severe, can cause the blood to become too viscous (thick), potentially leading to heart failure, heart attacks or strokes.

Common Questions

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.

It is not usually used to screen for polycythaemia (too many red blood cells), as the haematocrit - another routine part of a full blood count - is a more accurate test for this.
When is it requested?

Haemoglobin measurement is part of the full blood count (FBC) (which is requested for many different reasons), especially when your doctor suspects anaemia, and sometimes as part of a general health screen). It is often requested before operations to make sure you are fit for surgery and do not require a transfusion. The test is also repeated when monitoring bleeding or response to treatment of various anaemias.
What does the test result mean?
Normal haemoglobin values in an adult are approximately 120 to 180 g/L (12 to 18 g/dL) of blood but are influenced by the age, sex and ethnic origin in 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

vitamin deficiencies e.g. vitamin B12

bleeding

kidney disease

inflammatory disorders such as rheumatoid arthritis or infections

haemolysis (accelerated loss of red blood cells through destruction)

inherited haemoglobin defects such as thalassaemia or sickle cell anaemia

cirrhosis of the liver (during which the liver becomes scarred),

bone marrow failure

cancers that affect the bone marrow

infection
Is there anything else I should know?

Haemoglobin concentration decreases slightly during normal pregnancy.

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

Heavy 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.
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 supplements. If the bone marrow is not working properly, blood transfusions may be necessary. In kidney diseases and some cancers, treatment with the hormone erythropoietin ("Epo") can be effective.
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 tiredness, fainting, pallor (loss of normal skin colour), shortness of breath, a pounding sound in the ears or dizziness.
Can a healthy diet and good nutrition help keep optimal haemoglobin levels?

A healthy diet containing vegetables and sufficient iron is beneficial. Strict vegan vegetarians may require iron and vitamin B12 supplements.

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