A blood sample collected from a vein in your arm or by a finger-prick (children and adults) or heel-prick (newborns)
Ideally you should be reasonably hydrated when having a haemoglobin test or the result may be inaccurately high
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.
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:
- 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
- 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
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?
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?
Are there warning signs for abnormally low haemoglobin levels?
Can a healthy diet and good nutrition help keep optimal haemoglobin levels?
On This Site
Tests: Full blood count, haematocrit, Mean Corpuscular Haemoglobin Concentration (MCHC), Mean Corpuscular Haemoglobin (MCH), Mean Corpuscular Volume (MCV), Reticulocyte Count
Conditions: Anaemia, Sickle Cell Anaemia, Thalassaemia
Elsewhere On The Web
British Dietetic Association, Nutrients food facts
Patient, Vitamin B12 deficiency and Pernicious Anaemia
Macmillan Cancer Support, Side effects of Erythropoietin
Macmillan Cancer Support, Polycythaemia vera (PV)