Immunoglobulin A (IgA): What It's For (& What High or Low Levels Mean)

Immunoglobulin A, known mainly as IgA, is a protein found in large quantities within the mucous membranes, like he respiratory and gastrointestinal mucosa. It can also be found in breast milk, and can be passed on to the baby during breastfeeding to help develop immunity.

This immunoglobulin's main function is to defend the body and, therefore low IgA levels can favor the development of infections.

Female lab tech applying tourniquet on male patient for blood test

What is IgA for?

IgA's main function is to protect the body against infections and can initially be obtained through breastfeeding, in which the mother's immunoglobulins are transmitted to the baby. This protein can be classified into two types according to its location and characteristics, and each contain their own characteristics that are important for the body's defense:

  • IgA 1, which is mainly present in the blood and is responsible for immunological protection. It is capable of neutralizing toxins or other substances produced by foreign invaders.
  • IgA 2, which is present in mucous membranes and is associated with a secretory tissues. This type of IgA is resistant to most proteins produced by bacteria that are responsible for damaging healthy cells. Therefore, it is considered to be a first line of defense against infectious agents that enter the body through the mucous membranes.

Immunoglobulin A can be found in tears, saliva and breast milk, and is also present in the genitourinary, digestive and respiratory systems.

Normal IgA levels

Immunoglobulin A levels in the blood vary depending on the person's age and the laboratory's own reference levels:


Normal level 

Newborns (born to term) 

Up to 7.2 mg/dL

1 to 3 months

Up to 50 mg/dL

4 to 6 months

Up to 82.0 mg/dL

7 to 12 months

12.0 to 86.0 mg/dL

1 to 2 years old 12.0 to 108.0 mg/dL

3 years old

20.0 to 125.0 mg/dL

4 to 6 years old 30.0 to 190.0 mg/dL

7 to 9 years old

23.0 to 230.0 mg/dL

10 to 12 years old 50.0 to 265.0 mg/dL
13 to 16 years old 70.0 to 230.0 mg/dL

Adults (mean)

83.0 to 406.0 mg/dL

Adults (Women) 70.0 to 374.0 mg/dL

For the immunoglobulin A tests in saliva, levels for adults can vary from 2.0 to 8.0 mg/dL.

High IgA levels

High IgA can occur when there are changes in the mucous membranes, especially in the gastrointestinal and respiratory mucosa, as this immunoglobulin is mainly found in these areas. High IgA can occur with respiratory or intestinal infections, liver cirrhosis, skin infections or kidney infections.

It is important for other tests to be carried out, such as a complete blood count, total blood protein test or urine test, to determine the cause of high IgA and thus initiate the most appropriate treatment. 

Low IgA levels

Low IgA levels is normally genetic and does not present with symptoms. It is considered to be deficiency when levels of this immunoglobulin are lower than the reference values.

However, the low levels of IgA can favor the development of diseases, since the mucous membranes are unprotected. Therefore, in addition to being reduced from genetic factors, IgA deficiency may also be present in patients with:

  • Immune changes
  • Asthma
  • Respiratory allergies
  • Cystic fibrosis
  • Leukemia
  • Chronic diarrhea
  • Malabsorption syndrome
  • Newborns with rubella
  • People who have undergone bone marrow transplantation
  • Children infected with the Epstein-Barr virus

Normally, when there is a decrease in IgA, the body tries to compensate by increasing the production of IgM and IgG with the aim of fighting any diseases and keeping the body protected. In addition to checking IgA, IgM and IgG levels, the doctor should also order more specific tests to determine the underlying cause of low levels and to start treatment as recommended.

Also recommended: Immunoglobulin E (IgE): Normal Ranges & What High Levels Mean