Alternative Names serum antibody titre, titre-antibodies
Definition This test detects and measures the amount of antibodies in the blood. Antibodies are proteins made by the immune system. These antibodies are made 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.
Who is a candidate for the test? This test is normally performed to:
detect antibodies that the body has made to fight off a certain disease. Sometimes this is done to check whether a person has received a vaccine against a disease or has natural immunity due to having the disease in the past. Examples of diseases in which this test may be useful include:
Lyme disease, a bacterial infection that can be caught from a tick bite and commonly causes a rash, arthritis, and other problems
see if the immune system is creating antibodies to a person's own body. This response occurs in a variety of autoimmune disorders. Examples of autoimmune conditions in which this test may be useful include:
follow the course of some infections or conditions, which may be known or suspected. This can be done with several of the above listed diseases.
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 or hand. 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 vein chosen 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 laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.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.
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
If a person is being tested for antibodies that attack a person's own body, an abnormally high level of these antibodies often means the person has an autoimmune disease. The exact type of antibody can often help figure out which disease is present.
If a doctor 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, however, the immune system is on the attack and is making a lot of antibodies against the infection. This causes the antibody level to be much higher.
In other cases, a doctor may already know a person has an infection or disease. He or she may order the test 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 done again. In some conditions, the level of antibodies goes down over time if the treatment worked or is working.
Author: David T. Moran, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 27/02/2005 Contributors Potential conflict of interest information for reviewers available on request
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