Haemoglobin A2

Haemoglobin is the substance in the blood which carries oxygen (air) around the body and makes the blood look red in colour. The type of Adult haemoglobin which a person has is inherited through the genes. Genes always come in pairs one from the mother and one from the father. Therefore, every individual inherits two Adult Haemoglobin genes. The normal and most common Adult haemoglobin gene combination that an individual can inherit from their parents is Haemoglobin AA commonly written Hb AA.

During life in the womb and from very early in pregnancy every unborn baby produces a minor adult type haemoglobin called Haemoglobin A2, this haemoglobin is produced irrespective of the type of major Adult haemoglobin they have inherited from their parents.

From very early life in the womb the level of Haemoglobin A2 is between 2.2% – 3.5% and remains at this level at birth and through out adulthood.

For example, a person who has inherited normal adult Haemoglobin AA from their parents will have the following approximate Fetal, Adult and A2 (LINK TO A2 SECTION) haemoglobin levels:

Haemoglobin Newborn > 1 Year Old to Adulthood
Haemoglobin F 95% <1%
Haemoglobin A 5 – 10% >95%
Haemoglobin A2 2.2 – 3.5% 2.2 – 3.5%

A person who has inherited sickle cell trait (Hb AS) from their parents will have the following approximate Fetal, Adult and A2 haemoglobin levels:

Haemoglobin Newborn > 1 Year Old to Adulthood
Haemoglobin F 95% <1%
Haemoglobin A 5 – 10% >50%
Haemoglobin S 5 – 10% <50%
Haemoglobin A2 2.2 – 3.5% 2.2 – 3.5%

Haemoglobin A2 is considered a redundant haemoglobin since it is not very inefficient at carrying oxygen around the body, however, it is useful for helping the laboratory to diagnose some genetic mutations of haemoglobin, depending on the type of genetic mutation that has been inherited the level of A2 will rise or fall.