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ELISA stands for enzyme-linked immunoassay. It is a commonly used laboratory test to detect antibodies in the blood.

Alternative Names

Enzyme-linked immunoassay; EIA

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.

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.

How to Prepare for the Test

No special preparation is needed.

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.


Veins and arteries vary in size from one patient 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 light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)


Ashihara Y, Kasahara Y, Nakamura RM. Immunoassay and immunochemistry. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 44.

Review Date: 11/2/2014
Reviewed By: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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