What Is an Immunoglobulin Test?

This test checks the amount of certain antibodies called immunoglobulins in your body.

Antibodies are proteins that your immune cells make to fight off bacteria, viruses, and other harmful invaders. The immunoglobulin test can show whether there's a problem with your immune system.

Some conditions cause your body to make too many or too few immunoglobulins.

Having too few immunoglobulins in your blood gives you a greater chance of getting infections. Having too many could mean you have allergies or an overactive immune system.

Types of Immunoglobulin

Your body makes a few different types of immunoglobulin antibodies, including these:

Immunoglobulin A: IgA antibodies are found in the mucous membranes of the lungs, sinuses, stomach, and intestines. They're also in fluids these membranes produce, like saliva and tears, as well as in the blood.

Immunoglobulin G: IgG is the most common type of antibody in your blood and other body fluids. These antibodies protect you against infection by "remembering" which germs you've been exposed to before.

If those germs come back, your immune system knows to attack them. Your doctor can test for IgG to figure out whether you've been infected by certain kinds of bacteria or virus.

Immunoglobulin M: Your body makes IgM antibodies when you are first infected with new bacteria or other germs.

They are your body's first line of defense against infections. When your body senses an invader, your IgM level will rise for a short time. It will then begin to drop as your IgG level kicks in and increases to protect you long-term.

Immunoglobulin E: Your body makes IgE antibodies when it overreacts to substances that aren't harmful, such as pollen or pet dander. Your doctor will likely measure your IgE levels if you have a blood test to check for allergies.

Why You Might Need This Test

Your doctor might order an immunoglobulin test if you get a lot of infections -- especially infections of the sinuses, lungs, stomach, or intestines.

She may also order the test if you have:

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How the Test is Done

Doctors often measure IgA, IgG, and IgM together to get a snapshot of your immune function. A lab tech will usually take a sample of your blood by inserting a needle into a vein in your arm. The blood collects into a tube or vial.

Another way to do this test is with a sample of what’s called cerebrospinal fluid (CSF).

CSF surrounds your brain and spinal cord. The doctor will take a sample of this fluid with a lumbar puncture (often called a “spinal tap”).

For this, you go to an outpatient facility or a hospital. A technician will give you a shot in your back to help numb any pain.

You will likely lie on your side with your knees pulled up to your chest, or you sit on a table. The technician inserts a hollow needle between two vertebrae in your lower spine and removes a small amount of fluid so it can be tested.

What Do My Results Mean?

The sample will be sent to a lab for testing. This might take a few days.

Depending on your results, the doctor might need to do other tests, such as a:

If your immunoglobulin level is high, it might be caused by:

Low levels of immunoglobulins mean your immune system isn't working as well as it should. This can be caused by:

Just because your immunoglobulin level is high or low doesn't mean you have one of these conditions.

Each person's test can differ based on the method the lab uses to check the results. Talk to your doctor about your test results, and find out what you should do next.

WebMD Medical Reference Reviewed by Melinda Ratini, DO, MS on January 10, 2017

Sources

SOURCES:

American Association for Clinical Chemistry: "Quantitative Immunoglobulins: At a Glance," "Quantitative Immunoglobulins: Test Sample," "Quantitative Immunoglobulins: The Test."

Mayo Clinic: "Lumbar puncture (spinal tap): What you can expect."

Nemours Foundation: "Blood Test: Immunoglobulins (IgA, IgG, IgM)."

Pagana, Kathleen Deska. Mosby's Diagnostic and Laboratory Test Reference, 2016.

University of Rochester Medical Center: "Quantitative Immunoglobulins."

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