Other names: Hb

Haemoglobin is a protein, which is present in the red blood cells; it plays the essential role of carrying oxygen around the body. Low levels of haemoglobin are usually associated with anaemia. The haemoglobin test measures the amount of haemoglobin in the blood; the result determines the levels of oxygen that are carried around the body and, if levels are low, not enough oxygen is being transported around the body and this may cause the patient to feel tired and weak.

When is the test used?

The haemoglobin test is primarily used to test for anaemia; the test can be used to help doctors reach a diagnosis and it can also be used to determine the severity of a patient’s condition. Once they have been diagnosed, the patient may have repeated tests to see how they are responding to treatment. The test can also be used to test a patient for polycythaemia (when the body produces too many red blood cells).

The test is usually ordered when patients display symptoms of anaemia, including weakness, lethargy, fatigue, paleness and jaundice. The test may also be ordered if a patient is likely to need a blood transfusion after an operation. The haemoglobin test is part of the full blood count.

The test may also be ordered if a patient has problems with bleeding.

How is the test performed?

The test is done by collecting a sample of blood from the patient’s arm or finger; in most cases, a sample is taken from a vein in the arm but a finger prick test may also be carried out (this is usually done for children, as it is less traumatic). The needle is inserted into the vein and the blood is drawn out and collected in a syringe. Once the sample has been collected, it will be bottled, labelled and sent away to the laboratory for analysis.

In infants, a sample of blood will usually be taken from the heel; the heel is pricked with a needle and the blood is collected.

What do the test results show?

Normally, haemoglobin levels should be between 120 and 180 grams per litre of blood, but levels may vary according to the individual’s race, sex and age.

If levels of haemoglobin are higher than normal, this may indicate:

  • Dehydration
  • Lung disease
  • Excessive production of red blood cells (in the bone marrow)

If levels of haemoglobin are lower than normal, this may indicate:

  • Iron deficiency
  • Liver cirrhosis
  • Kidney disease
  • Bone marrow failure
  • Cancers that affect the bone marrow
  • Deficiencies of certain vitamins and minerals

Haemoglobin levels are usually slightly lower than normal during pregnancy.

People who smoke and those who live at high altitude usually have higher levels of haemoglobin in their blood.

Levels of haemoglobin may vary according to the time of day; levels are usually higher in the morning.

Specific Blood Tests

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