An enzyme-linked immunoassay (EIA) or enzyme-linked immunosorbent assay (ELISA) is a blood or urine test that can aid in the diagnosis of many infections and inflammatory conditions. This is a simple test that does not cause any side effects. Your EIA can help diagnose the cause of your symptoms and is used to guide your therapy.
Often, you may not specifically know that an EIA test is going to be performed unless you carefully review the order form. EIA is a laboratory technique, but it does not change the way blood is drawn.
This test works by producing a color change in a solution when your sample is examined in the laboratory. The color change occurs as a result of a chemical reaction described as an enzyme-antibody reaction.
Purpose of the test
An EIA test is used for children and adults. You may need to have an EIA test if you develop symptoms or have been exposed to certain infections. This test is also used to help diagnose allergies and some autoimmune diseases.
An EIA test can also be used to identify certain medications and for drug screening.
Some of the infections that can be detected by the EIA include:
- VIH virus
- hepatitis C virus
- hepatitis B virus
- virus del herpes
- Lyme's deseaseBorrelia burgdorferibacteria
- Syphilis pale treponemabacteria
Other substances that can be detected by an EIA test include:
- Cancer markers:Cancer markers are proteins or hormones made by some types of cancer and can be detected before the cancer is large enough to be seen on imaging tests.
- Hormone levels:Many steroid hormones and reproductive hormones can be detected with this test.
- Inflammatory markers: Inflammatory and autoimmune diseases can produce antibodies or other proteins that can be detected by EIA.
- Certain medications:Opioids, pain relievers, and sedatives are among the long list of medications that can be identified by the EIA.
An EIA test can be used to help identify if you are allergic to a particular substance. An allergy is characterized by the reaction of an antibody (immune protein) to a harmless substance described as an allergen. An allergen is a substance that induces an allergic reaction.
Types of allergy tests
Another use of EIA is for drug detection. A blood or urine sample can be used to detect the presence of certain drugs, such as cocaine or hallucinogens. This is typically used in a setting such as employment associated drug screening.
Risks and contraindications
An EIA is a simple and risk-free test. If you are healthy enough to tolerate having your blood drawn, you should not have any contraindications to having this test.
If you have bleeding problems,hypotension (low blood pressure), oanemia (low blood cell count and/or red blood cell function), your doctor may give you special precautions when you have this test.
Before the test
Generally, no preparation is needed before having an EIA. If your doctor wants you to stop taking medicine or being exposed to any substance, you will be given specific instructions before the test.
You should be prepared to spend about an hour at the site where your blood or urine will be drawn. It's a good idea to ask about the expected wait time before taking the test, especially if you have other activities planned for the day.
The blood draw procedure itself usually only takes about five minutes, but the time spent getting in, completing the paperwork, and waiting your turn can take longer.
You can go to your doctor's office, a lab in a medical building, or a hospital to have your blood or urine drawn for EIA. Your health care provider and health insurance provider can provide you with a list of approved places you can go to have this test done.
what to wear
For an EIA, blood will usually be drawn from a vein in the antecubital area (the inside of your arm at the elbow) or from a vein in your hand.
When performing this test, you should wear a shirt that is short-sleeved or with sleeves that are easy to roll up to above the elbows. People who go to work after having their blood drawn often like to wear long sleeves to cover the bandage.
If you are going to have a urine test, it is a good idea to wear clothing that is easy to get on or off so that you can collect your urine while holding the sample container.
Food and drink
Unless your doctor has given you specific instructions to avoid a particular food or drink, you may eat and drink as usual before the test, without any restrictions.
Cost and health insurance.
Depending on your health plan, the cost of this test may be covered in whole or in part. You may have to pay a copay even if your health insurance covers most of the cost of the test. It is best to check with your health insurer in advance and verify the cost with the laboratory where you are performing the test.
An EIA blood test costs between $50 and $200. Note that this cost may be higher if you are testing for multiple allergens. An EIA urine test costs between $20 and $40. This can vary depending on the number of substances being tested.
The cost of an on-the-job drug test will probably not be covered by your health insurance, and you or your employer will have to pay for it.
Be sure to bring your insurance card, an ID card, and some method of payment when you take the test. Before you are authorized to have the test performed, you may be required to pay your copay or provide payment in full if you will be paying for the test yourself.
during the exam
When you go to take the EIA test, you will meet the staff who will help you register and fill out the forms. You will also find a nurse orphlebotomistwho will draw blood or help with urinalysis.
Before the test, you will be asked to log in, show your test order, and present your identification and insurance information. You may also be asked to wait your turn if they are not ready for you right away.
throughout the test
A nurse or phlebotomist will call you to have your blood drawn. You will be asked to sit down. They will also usually ask which hand he writes with or which arm he prefers to have blood drawn from. They usually try to avoid drawing blood from the arm you write with.
A tourniquet or band will be placed around your arm. Your nurse or phlebotomist will then feel the vein and clean the area around it.
A small needle will then be inserted into your vein, and a tube will usually be placed on the other side of the needle to collect the blood. The needle will be inserted into your arm for less than a minute. When the needle is withdrawn, a small cotton or gauze ball will be placed on the puncture site with a little pressure to stop bleeding. You may be asked to put pressure on it for a few minutes.
7 tips to facilitate blood collection
A urine sample
If you are having aurine tests, they may tell you how to collect your urine sample. You will be taken to a private bathroom, given a container to collect your urine, and instructed to clean yourself before collecting it to avoid contamination.
Once the bleeding stops (this usually takes less than a minute), a bandage will be placed over the puncture site and you are free to leave.
If you feel dizzy or lightheaded, or if you continue to bleed from the puncture site after the test, be sure to tell your nurse or phlebotomist.
You can drive home after the test and you do not need to be accompanied by anyone. After the exam, the bandage should be left on the puncture site for about 24 hours to keep it clean.
On the first day after the test, it's a good idea to avoid heavy lifting with the arm used to draw blood.
Most people have no problems after an EIA test. Some people notice pain or small bruises around the puncture site, but this should not last more than a few days.
manage side effects
If you have health problems or have anemia, you may experience some side effects after having your blood drawn. Symptoms can include dizziness, lightheadedness, and fatigue.
If you have a bleeding condition, the puncture site may continue to bleed.
If you have severe or persistent pain, bruising, bleeding, or dizziness after your blood draw, talk to your doctor about it.
Interpretation of results
EIA test results generally take anywhere from a few hours to a few days. Your doctor should be able to give you a time frame to wait for the results, and if you will be notified, you should call to verify or receive them electronically.
How the EIA works
The interpretation of your EIA test is based on a color change. This test can be read as positive or negative, and can also produce a quantitative result, which compares the reaction to the standard or normal range.
Because this test is used for many different indications, each indication has its own normal range and standard result, which will be included in the test report.
An EIA uses a sample of your blood or urine. The sample is exposed to a protein that is known to bind to a very specific substance, such as an antibody. Because EIA is used for a wide variety of diagnoses, the protein used for your test depends on the condition for which you are being tested. For example, if you have an EIA to diagnose hepatitis B, this test cannot be positive or negative for a different condition, such as HIV.
After your sample is exposed to a selected protein, a substance in your blood sample can bind to the protein. After this initial step, the residue is washed and an enzyme is introduced into the solution. The enzyme is selected because it binds to the protein that was initially loaded with your sample. If a binding reaction occurs, the enzyme induces a color change.
If the color of the solution changes, this is considered an indication that the substance being tested for is present and is considered a "positive" test. If no color change occurs, it is considered a negative test.
Sensitivity and specificity
EIA tests are very sensitive and very specific. The antibodies used in an EIA test only bind to the substance being tested for and nothing else, making the result specific. The color change can occur in response to a very small amount of the substance being tested, making these tests very sensitive.
That said, all tests can produce false positives (incorrectly saying you have a diagnosis, even when you don't) and false negatives (incorrectly saying you don't have the diagnosis, even when you do). The false positivity or false negativity rate is different for each condition tested by the EIA.
You may need a follow-up EIA in some situations. If you are having an allergy test, you may need to repeat the test after a delay to see if there has been any change in your allergic reaction.
When the EIA test has been used to detect an infection, it may not need to be repeated if symptoms improve with treatment. However, some infections, such as HIV, need to be controlled and you may need to repeat the test at regular intervals.
If you obtained your EIA for a drug test at work, retesting is based on your employer's policy.
A word from Verywell
There is a high chance that you will need to take an EIA test at some point. The test is very safe with rare side effects.
The results should be interpreted in light of standard measurements and also with attention to your general health and symptoms. This test can be useful for many indications, and the results can provide information about your health that other tests do not normally provide.