Immunoglobulins (IgG, IgA, IgM): what they are, what they tell you and when they’re tested

Immunoglobulins are the antibodies your immune system makes to fight viruses and bacteria. The test measures three kinds: IgG, IgA and IgM. It shows whether you make enough, too few or too many.

When they’re tested

Doctors mostly order them when you get infections that keep coming back or last too long, such as sinusitis, bronchitis or pneumonia. They are also used when a protein electrophoresis shows something unusual, or to follow some blood conditions.

They are also measured before a coeliac test: if your IgA is very low, the most common test can come back falsely negative.

It is not a routine test for people who feel well and rarely get ill. That is why Rosa does not test them. Instead it looks at white blood cells and lymphocytes, the cells that make antibodies, and albumin, which shows how much protein is in your blood.

What they tell you, and what they do not

Each kind has a job. IgG is the most plentiful and protects you for a long time, including after a vaccine. IgA guards the linings of your gut, nose and airways. IgM is the first to appear when you meet a new infection.

Low levels can mean your immune system makes few antibodies, or that your body loses them, for example through the kidneys or the gut. High levels are often seen with long infections, liver disease or autoimmune conditions.

The test does not tell you the cause on its own. Nor does it say whether your antibodies work well: for that your doctor may ask for other tests, such as your response to a vaccine.

That is why they are read together with other tests:

Normal immunoglobulin levels

The lab decides what is normal, and it changes a lot with age: children have lower values. For adults, many labs give roughly: IgG 700 to 1600 mg/dL, IgA 70 to 400 mg/dL, IgM 40 to 230 mg/dL.

Some reports use g/L: just divide by a hundred. For example, 1000 mg/dL is 10 g/L.

With age, IgG and IgA tend to rise a little. Women have, on average, slightly lower IgA and IgG and slightly higher IgM. People who smoke often have lower IgA and IgG. You do not need to fast.

If your immunoglobulins are high or low

Why they change

The most common causes, low ones first, then high ones.

What can skew the result

A few things change the value without any disease.

When to worry

Talk to your doctor if:

Frequently asked questions

What are normal immunoglobulin levels? For adults, many labs give roughly: IgG 700 to 1600 mg/dL, IgA 70 to 400, IgM 40 to 230. Children have lower values. The range on your own report is what counts.

What does low IgA mean? Often it is IgA deficiency, the most common antibody shortage. Many people have no symptoms, others get more infections of the nose, airways or gut. It is also more common in people with coeliac disease, and it changes how the coeliac test is done.

Should I worry about high IgG? Usually not. It often comes from a recent or long infection, inflammation or the liver. If it stays high, your doctor may ask for an electrophoresis to see whether only one kind of antibody is rising.

What does high IgM mean? IgM rises first when you meet a new infection. Often that is all it is. If it stays high for no reason, your doctor looks further.

Does Rosa test immunoglobulins? No. Rosa measures white blood cells, lymphocytes and albumin, which say a lot about your defences and the proteins in your blood. If your doctor wants immunoglobulins, they order them separately.

Sources