The antibody titer detects and measures the amount of antibodies in the blood. Antibodies are proteins made by the immune system to attack a real or imagined threat. For example, antibodies may be made in some cases to attack bacteria causing an infection. In other cases, however, antibodies may be made to attack a person's own body. This situation is termed "autoimmune" disease.
Who is a candidate for the test?
One common function of the antibody titer is to detect antibodies that the body has made to fight off a certain disease. Sometimes this is done to check whether a person has gotten a vaccine against a disease, and sometimes to discover natural immunity due to having the disease in the past.
This test may be useful in the diagnosis of the following diseases:
Epstein-Barr virus infection, which is the main cause of infectious mononucleosis
hepatitis A, hepatitis B, hepatitis C, or hepatitis D, which are viral infections that primarily affect the liver
Lyme disease, which is a bacterial infection that can be caught from a tick bite
rubella, formerly known as German measles
- syphilis, a sexually transmitted disease
Another common function of the antibody titer is to see if the immune system is creating antibodies to a person's own body. This response occurs in a variety of autoimmune disorders. Following are some examples of autoimmune conditions in which this test may be useful:
Graves' disease, a condition that results in an overactive thyroid gland
Hashimoto's thyroiditis, a condition that results in an underactive thyroid gland
myasthenia gravis, a condition that causes weakness in the muscles
rheumatoid arthritis, which can cause joint inflammation and deformity
- systemic lupus erythematosus, an inflammatory condition that affects many body systems
The antibody titer also is useful in following the course of known or suspected infections. For instance, the level of certain antibodies to syphilis will decline following successful treatment.
How is the test performed?
To measure the levels of antibodies in the blood, a blood sample is needed. This is usually taken from a vein on the forearm. First, the skin over the vein is cleaned. Next, a strong rubber tube, or tourniquet, is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them.
A fine needle is gently inserted into the chosen vein and the tourniquet is removed. Blood flows from the vein through the needle. It is collected in a syringe or vial for testing in the lab. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test?
No preparation is generally needed for an antibody titer.
What do the test results mean?
The meaning of the results depends on why the test was done. If the test was done to see if a person has immunity to a disease:
- a level within or above the normal range means the person is probably protected from the disease
- a level below the normal range means the person is probably not protected from the disease
A person with an autoimmune disease will have an abnormally high level of antibodies. Knowing the exact type of antibody can often help determine which disease is present. If a healthcare professional suspects a certain infection, he or she may order this test when the person is first seen. A second test done a week or two later can help determine if the infection is or was present.
If a healthcare provider suspects a certain infection, he or she may order this test when the person is first seen. A second test done a week or two later can help determine if the infection is or was present. When an infection first starts, the level of antibodies against the infection is usually low. This is because the immune system has just become aware of the infection. A week or two later, the immune system is on the attack. It is making a lot of antibodies against the infection. This causes the antibody level to be much higher.
In other cases, a healthcare provider may already know a person has an infection or disease. An antibody titer may be ordered to see if the condition responds to treatment. In this case, the test is done before treatment is started. After treating the condition for a certain amount of time, the test can be repeated. In some conditions, the level of antibodies goes down over time if the treatment worked or is working.
Tabers Cyclopedic Medical Dictionary, F.A.Davis, 1993
Illustrated Guide to Diagnostic Tests, Springhouse, 1998
Mosby's Manual of Diagnostic and laboratory Tests, Kathleen Pagana and Timothy Pagana, 1998