Elisa (Enzyme-Linked Immunosorbent Assay)

Elisa enzyme-linked immunosorbent assay is an immunological assay commonly used to measure antibodies, antigens, proteins, and glycoproteins in biological samples. Some examples include diagnosis of HIV infection, pregnancy tests, and measurement of cytokines or soluble receptors in cell supernatant or serum. ELISA assays are generally carried out in 96 well plates, allowing multiple samples to be measured in a single experiment. These plates need to be special absorbent plates (e.g. NUNC Immuno plates) to ensure the antibody or antigen sticks to the surface. Each ELISA measures a specific antigen, and kits for a variety of antigens are widely available.

An enzyme-linked immunosorbent assay, also called ELISA or EIA, is a test that detects and measures antibodies in your blood. This test can be used to determine if you have antibodies related to certain infectious conditions. Antibodies are proteins that your body produces in response to harmful substances called antigens.

An ELISA test may be used to diagnose:

• HIV, which causes AIDS
• Lyme disease
• pernicious anemia
• Rocky Mountain spotted fever
• rotavirus
• squamous cell carcinoma
• syphilis
• toxoplasmosis
• varicella-zoster virus, which causes chickenpox and shingles
• Zika virus

ELISA is often used as a screening tool before more in-depth tests are ordered. A doctor may suggest this test if you’re having signs or symptoms of the conditions above. Your doctor may also order this test if they want to rule out any of these conditions. 

How is the test performed?

The ELISA test is simple. You’ll probably need to sign a consent form, and your doctor should explain the reason for doing the test.

The ELISA test involves taking a sample of your blood. First, a healthcare provider will cleanse your arm with an antiseptic. Then, a tourniquet, or band, will be applied around your arm to create pressure and cause your veins to swell with blood. Next, a needle will be placed in one of your veins to draw a small sample of blood. When enough blood has been collected, the needle will be removed and a small bandage will be placed on your arm where the needle was. You’ll be asked to maintain pressure at the site where the needle was inserted for a few minutes to reduce blood flow.

This procedure should be relatively painless, but your arm may throb a little after it’s done.

The blood sample will be sent to a laboratory for analysis. In the lab, a technician will add the sample to a petri dish containing the specific antigen related to the condition for which you are being tested. If your blood contains antibodies to the antigen, the two will bind together. The technician will check this by adding an enzyme to the petri dish and observing how your blood and the antigen react.

You may have the condition if the contents of the dish change color. How much change the enzyme causes allows the technician to determine the presence and amount of antibodies.

How do I prepare for the test?

There’s no special preparation for this test. The blood draw lasts only a few moments and is mildly uncomfortable. Tell your healthcare provider if you have a fear of needles or become lightheaded or faint at the sight of blood or needles.

Are there any risks?

There are very few risks associated with this test. These include:

• infection
• feeling faint
• bruising
• bleeding more than usual

Make sure to tell your doctor before the test if you’ve had trouble giving blood in the past, bruise easily, or have a bleeding disorder such as hemophilia.

What do the results mean?

How the test results are reported varies based on the laboratory that conducts the analysis. It also depends on the condition for which you’re being tested. Your doctor should discuss your results and what they mean. Sometimes, a positive result will mean that you don’t have the condition.

False positives and false negatives can occur. A false-positive result indicates you have a condition when you don’t. A false-negative result indicates you don’t have a condition when you do. Because of this, you may be asked to repeat the ELISA in a few weeks, or your doctor may order more sensitive tests to confirm or refute the results.

What else do I need to know?

Although the test itself is relatively simple, waiting for the results or being screened for conditions such as HIV can cause a lot of anxiety. It’s important to remember that no one can force you to take the test. It’s voluntary. Make sure that you understand the laws in your state or the policy of the healthcare facility for reporting positive HIV results.

Discuss the test with your provider. Remember that diagnosing any possible infectious disease is the first step toward getting treatment and protecting others from the infection.