Haemoglobin
Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.
A haemoglobin test measures the level of haemoglobin in a blood sample, a protein in red blood cells that carries oxygen around the body. It is used to assess oxygen-carrying capacity and help diagnose conditions such as anaemia or disorders affecting red blood cells.
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.
Common questions
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.
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.
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
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.
No, except that dehydration can temporarily increase 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.
Women of childbearing age may have temporary decreases during menstrual periods and pregnancy.
Some warning signs are tiredness, fainting, pallor (loss of normal skin colour), shortness of breath, a pounding sound in the ears or dizziness.
A healthy diet containing vegetables and sufficient iron is beneficial. Strict vegan vegetarians may require iron and vitamin B12 supplements.