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ELISA blood test
Enzyme-linked immunoassay; EIA
ELISA stands for enzyme-linked immunoassay. It is a commonly used laboratory test to detect antibodies in the blood. An antibody is a protein produced by the body's immune system when it detects harmful substances, called antigens.
Antibodies
An antibody is a protein produced by the body's immune system when it detects harmful substances, called antigens. Examples of antigens include micr...
How the Test is Performed
A blood sample is needed. Most of the time, blood is drawn from a vein located on the inside of the elbow or the back of the hand.
Drawn from a vein
Venipuncture is the collection of blood from a vein. It is most often done for laboratory testing.
The sample is sent to a laboratory where the targeted antibody or antigen is linked to a specific enzyme . If the target substance is in the sample, the test solution turns a different color.
Antigen
An antigen is any substance that causes your immune system to produce antibodies against it. This means your immune system does not recognize the su...
Enzyme
Enzymes are complex proteins that cause a specific chemical change in all parts of the body. For example, they can help break down the foods we eat ...
How to Prepare for the Test
No special preparation is needed.
How the Test Will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
This test is often used to see if you have been exposed to viruses or other substances that cause infection. It is also used to screen for current or past infections.
Normal Results
Normal values depend on the type of substance being identified. Some laboratories use different measurements or test different samples. Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
What Abnormal Results Mean
Abnormal values depend on the type of substance being identified. In some people, a positive result may be normal.
Risks
Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
References
Aoyagi K, Ashihara Y, Kasahara Y. Immunoassay and immunochemistry. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods . 23rd ed. St Louis, MO: Elsevier; 2017:chap 44.
Murray PR. The clinician and the microbiology laboratory. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Updated Edition . 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 16.
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Blood test - illustration
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.
Blood test
illustration
-
Blood test - illustration
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.
Blood test
illustration
Review Date: 12/10/2016
Reviewed By: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
