IgA blood test (immunoglobulin A)

Immunoglobulin A (IgA) is one of several classes of antibodies (immunoglobulins) produced by the immune system. Most of it acts not in the blood but on the mucous membranes — the surfaces of the nose, throat, lungs and gut, and also in saliva, tears and breast milk — and it is the first line of defence against microorganisms that are inhaled or swallowed. The amount of IgA measured in blood indirectly shows how this mucosal immunity is working. The immunoglobulin test (most often together with IgG and IgM) is carried out when a person gets infections often, or when certain blood cell diseases are suspected, because certain tumours (myeloma, for example) can produce too much of one class of immunoglobulins. The result is always assessed together with the other immunoglobulins and the overall clinical picture, rather than in isolation.

• When infections keep recurring often — especially if the same causative organism returns repeatedly
• With frequent infections of the sinuses, throat and ears, including streptococcal throat infection
• When respiratory tract infections keep recurring — pneumonia, bronchitis
• With persistent digestive tract problems and diarrhoea with no clear cause
• When infections are caused by unusual microorganisms, or are unusually severe
• Where immune system diseases involving antibody production, or certain blood cancers, are suspected

The exact numeric range depends on the laboratory method and on age, so you will find it on your own result sheet next to the value. MedlinePlus notes that the result is assessed together with IgG and IgM, rather than in isolation, so it is worth discussing the specific value with a doctor.

A raised amount of immunoglobulins (IgA among them) is, per MedlinePlus, linked to autoimmune diseases, liver diseases (hepatitis, cirrhosis) and chronic infections. In some cases it is also raised by certain blood cancers, which often cause a very high level of one class of immunoglobulin and low levels of the other classes. The result is always assessed together with IgG, IgM and other tests, rather than in isolation.

• An autoimmune disease
• Hepatitis
• Cirrhosis
• A chronic infection
• Certain blood cancers — multiple myeloma, chronic lymphocytic leukaemia, lymphoma, Waldenström macroglobulinaemia; these often cause a very high level of one class of immunoglobulin and low levels of the other classes

What usually comes next with a raised result:

• Discussing the result together with the IgG and IgM values, rather than in isolation
• Liver function tests, if liver disease is suspected
• Further tests, if the doctor suspects a disease involving antibody production or a blood cancer
• Discussing symptoms and the history of infections with a doctor

Reduced IgA: what it can mean

A reduced IgA, per MedlinePlus, may point to kidney disease, severe burns, poor absorption of nutrients or poor nutrition, and also to complications of diabetes or of kidney failure. One of the causes is inherited common variable immunodeficiency (CVID), because of which the body produces too few antibodies.

• Kidney disease
• Severe burns
• Malabsorption disorders and poor nutrition
• Complications of diabetes or of kidney failure
• Common variable immunodeficiency (CVID) — an inherited condition

What usually comes next with a reduced result:

• Discussing the history of frequent infections with a doctor
• Assessment of the other immunoglobulins (IgG, IgM) and of a full blood count
• Kidney function tests, if kidney disease is suspected
• The option of genetic testing, if an inherited immunodeficiency is suspected