ELISA Tests Procedure and Results

ELISA, or EIA, is an acronym for enzyme-linked immuno assay. ELISA is a test that detects and measures antibodies in your blood.

This test can be used to determine if you have antibodies that are related to certain infectious conditions. Antibodies are proteins that the body produces in response to harmful substances (antigens).

The purpose of an ELISA is to determine if a particular protein is present in a sample and if so, how much. There are two main variations on this method: you can determine how much antibody is in a sample, or you can determine how much protein is bound by an antibody.

The distinction is whether you are trying to quantify an antibody or some other protein. In this example, we will use an ELISA to determine how much of a particular antibody is present in an individuals blood.

ELISAs are performed in 96-well plates which permits high throughput results. The bottom of each well is coated with a protein to which will bind the antibody you want to measure.

Whole blood is allowed to clot and the cells are centrifuged out to obtain the clear serum with antibodies (called primary antibodies). The serum is incubated in a well, and each well contains a different serum.

A positive control serum and a negative control serum would be included among the 96 samples being tested.

After some time, the serum is removed and weakly adherent antibodies are washed off with a series of buffer rinses. To detect the bound antibodies, a secondary antibody is added to each well. The secondary antibody would bind to all human antibodies and is typically produced in a rodent.

Attached to the secondary antibody is an enzyme such as peroxidase or alkaline phosphatase. These enzymes can metabolize colorless substrates (sometimes called chromagens) into colored products.

After an incubation period, the secondary antibody solution is removed and loosely adherent ones are washed off as before. The final step is the addition the enzyme substrate and the production of colored product in wells with secondary antibodies bound.

An ELISA test may be used to diagnose:

  • HIV (the virus that causes AIDS)
  • Lyme disease
  • pernicious anemia
  • Rocky Mountain spotted fever
  • rotavirus
  • squamous cell carcinoma
  • syphilis
  • toxoplasmosis
  • varicella zoster virus (which causes chicken pox and shingles)

If your blood contains antibodies to one of these conditions, it is likely that you have it or have had it in the recent past.

Often, ELISA is used as a screening tool before other, more in-depth tests are ordered. A doctor may suggest this test if you are experiencing signs or symptoms of the conditions above, or if the doctor wants to rule out any of these conditions.

How the Test Is Performed

The test is simple and straightforward. You will probably need to sign a consent form, and your healthcare provider should explain the reason for doing the test.

A healthcare professional will take a sample of your blood. First, he or she will cleanse your arm with an antiseptic. Your healthcare provider will then apply a tourniquet, or band, around your arm to create pressure and cause your veins to swell with blood.

Next, your provider will place a needle in one of your veins and draw a small sample of blood. When enough blood has been collected, he or she will remove the needle and place a small bandage on your arm where the needle was.

You will be asked to elevate or flex your arm to reduce blood flow.

This procedure should be relatively painless, though your arm may throb a little after the procedure.

The blood sample will be sent to a laboratory for analysis. In the lab, a technician adds the sample to a petri dish containing the specific antigen (foreign substance such as a virus that causes your immune system to respond) 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.

If the contents of the dish change color, you may have the condition. How much change the enzyme causes allows the technician to determine the presence and amount of antibody.

Who Should Be Tested?

Your healthcare provider may suggest this test if you are at risk for or show symptoms of the conditions listed above. It is common for pregnant women to have this test to screen for HIV.

The test is voluntary, so expectant mothers may opt not to have this screening.

Preparing for the Test

There is 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 faint at the sight of blood.

Are There Any Risks?

There are very few risks associated with this test. However, any time the skin is broken there is a potential for infection. According to the National Institutes of Health (NIH), feeling faint, bruising, and bleeding more than usual are all possible complications (NIH, 2010).

If you have had trouble giving blood in the past, bruise easily, or suffer from a bleeding disorder such as hemophilia, make sure to tell your doctor before the test.

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 are being tested.

Your doctor should discuss your results and what they mean. Sometimes, a “positive” result will mean that you do not have the condition.

False positives and false negatives can occur. This means that results indicate that you have a condition when you actually do not, or indicate that you don’t have a condition when you do.

Because of this, you may be asked to repeat the ELISA again in a few weeks, or your doctor may order other, more sensitive tests to confirm or refute that you have the condition.

 

Source & More Info: Healthline and

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