- immunochemical assay
An immune assay is a special method of testing to measure or detect certain substances in the body. This sophisticated test uses the properties of the immune or infection-fighting system. It is usually used when the amount of material to be detected is very small. It is most commonly performed on a sample of blood, though other body fluids may be used.
Who is a candidate for the test?
The immune assay has many uses, including:
- testing for infections, such as human immunodeficiency virus (HIV), Lyme disease, or chlamydia
- testing for autoimmune disorders, which are conditions in which a person's immune system attacks his or her own body. These disorders include systemic lupus erythematosus and rheumatoid arthritis.
- testing for hormone levels, such as some types of pregnancy testing or thyroid function tests, used to help diagnose conditions of the thyroid gland
- testing for certain cancers, such as the blood cancers leukemia and multiple myeloma
- detecting the presence, or measuring the level, of medications in a person's body
Other uses of this testing method are also possible. The immune assay is being used more and more commonly.
How is the test performed?
First, a sample of the fluid to be tested is obtained. This may mean collecting blood saliva, urine, or cerebrospinal fluid (CSF) sample. CSF is the fluid that surrounds the brain and spinal cord, and is obtained with a
spinal tap. The fluid to be tested is collected into a special container and sent to the lab for testing.
There are many different methods of performing the test. Most involve mixing antibodies or antigens with the body fluid being tested. Antibodies are special proteins made by the immune system. The body makes these proteins when there is an infection or other threat. An antigen is any substance that causes the immune system to respond or attack. It might be bacteria, a virus, a medications, or even the person's own body.
If the healthcare professional is trying to detect antibodies in the blood, antigens are usually used in the test. If the goal is to detect antigens, antibodies are used. For example, a test may be done to look for Lyme disease antibodies. Pieces of the bacteria that cause Lyme disease, the antigen, are put in a container. The person's blood is then mixed with the antigen. If the person has antibodies against the Lyme disease bacteria, they will react with the antigen.
This reaction can be detected in different ways. One of the most common is to utilize a chemical which will detect the presence of the antigen-antibody complex in the sample by turning a different color. A positive reaction means the person may have Lyme disease. If no reaction occurs, the person probably does not have the condition.
What is involved in preparation for the test?
Usually, no preparation is needed for this test.
What do the test results mean?
Interpretation of the test results depends on why the test was ordered. For example, the results of one test may indicate that a woman is or is not pregnant. The results of another test may mean that a person does or does not have a certain infection. The healthcare professional can discuss the results and what they mean with the individual.
Harrison's Principles of Internal Medicine, 1998, Fauci et al.