What Is an Immunoglobulin Test and Why Is It Done?

An immunoglobulin (im-yeh-no-GLOB-yeh-len) test measures the level of types of antibodies in the blood.

Doctors may check immunoglobulin levels:

• to see if a person has an infection or is protected from getting an infection (is immune to it)
• to help diagnose immunodeficiencies (when the immune system is less active than it should be). Doctors may suspect an immunodeficiency in a child who gets a lot of infections or unusual infections.
• as part of an evaluation for allergies or autoimmune conditions (when the immune system overreacts) like juvenile idiopathic arthritis, lupus, and celiac disease

What Are Antibodies?

Antibodies (also called immunoglobulins) are proteins the immune system makes to recognize and get rid of germs it thinks are harmful. These include bacteria, viruses, and allergens — the things that can bring on allergies, like pollen.

The body makes different antibodies to fight different things. For example, the antibody for chickenpox isn't the same as the antibody for mononucleosis. Sometimes, the body may even mistakenly make antibodies against itself, treating healthy organs and tissues like foreign invaders. This is called an autoimmune disease.

What Are the Types of Antibodies?

The types of antibodies are:

• Immunoglobulin A (IgA): It's found in the linings of the respiratory tract and digestive system, as well as in saliva (spit), tears, and breast milk.
• Immunoglobulin G (IgG): This is the most common antibody. It's in blood and other body fluids, and protects against bacterial and viral infections. IgG can take time to form after an infection or immunization (vaccine).
• Immunoglobulin M (IgM): This is found mainly in blood and lymph fluid. IgM is the first antibody the body makes when it fights a new infection.
• Immunoglobulin E (IgE): It’s normally found in small amounts in the blood. IgE can be higher when the body overreacts to allergens or is fighting an infection from a parasite.
• Immunoglobulin D (IgD): This is the least understood antibody, and there are only small amounts of it in the blood.

Top Things to Know

• An immunoglobulin test blood test checks how much of a certain immunoglobulin (or antibody) is in the blood.
• The tests can help find things like infections, immune system problems, and allergies.
• Kids might need to stop taking certain medicines or not eat or drink before the blood test.
• Your doctor can explain what it means if the immunoglobulin level is high or low.

How Can I Help My Child Prepare for a Blood Test?

To help kids get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test. If your child is nervous about it, work together on ways to stay calm. Deep breathing or even imagining being in a peaceful place that makes your child feel safe and relaxed can help.

What Do Immunoglobulin Test Results Mean?

Your doctor will explain what the results of the immunoglobulin test mean for your child. “Normal” levels of antibodies vary based on things like age and gender.

High levels mean there’s too much of the antibody. This can be a sign that the body is fighting an infection, had certain infections in the past, or overreacts to allergens, which can lead to an allergic reaction.

With low levels of the antibody, there’s too little of it. This may mean there’s an immune system condition.

What Else Should I Know?

Depending on the results of the immunoglobin test, kids may need other tests to see if they have a certain condition for sure. If you have questions about immunoglobin tests or what the results mean, talk with your doctor.