context: 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. Your body makes a few different types of immunoglobulin antibodies, including these: Immunoglobulin A: Ig A 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: Ig G 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 Ig G to figure out whether you've been infected by certain kinds of bacteria or virus. Immunoglobulin M: Your body makes Ig M 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 Ig M level will rise for a short time. It will then begin to drop as your Ig G level kicks in and increases to protect you long-term. Immunoglobulin E: Your body makes Ig E antibodies when it overreacts to substances that aren't harmful, such as pollen or pet dander. Your doctor will likely measure your Ig E levels if you have a blood test to check for allergies. 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: Diarrhea that doesn't go away Unexplained weight loss Fevers that can't be explained by another cause Skin rashes Allergies Sickness after traveling HIV/ AIDS or multiple myeloma (a type of cancer), or another condition that needs to be monitored Doctors often measure Ig A, Ig G, and Ig M 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 âspinal tapâ). 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. 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: Complete blood count ( CBC) Protein blood test Urine test to check for kidney problems If your immunoglobulin level is high, it might be caused by: Allergies Chronic infections An autoimmune disorder that makes your immune system overreact, such as rheumatoid arthritis, lupus, or celiac disease Liver disease Inflammatory bowel disease Cancer, such as multiple myeloma, lymphoma, or leukemia Low levels of immunoglobulins mean your immune system isn't working as well as it should. This can be caused by: Medicines that weaken your immune system, such as steroids Diabetes complications Kidney disease or kidney failure A weakened immune system that you were born with or developed (as with HIV/ AIDS) 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.