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ELISA

Definition

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

Alternative Names

Enzyme-linked immuno assay; EIA

How the test is performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. This is called a venipuncture.

The sample is sent to a laboratory where the targeted antibody or antigen is linked to  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.

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

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 often used to screen for current or past infections.

Normal Values

Normal values depend on the type of substance being identified. Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What abnormal results mean

Abnormal values depend on the type of substance being identified. In some people, a positive result may be normal.

What the risks are

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)

References

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: Saunders Elsevier; 2011:chap 44.


Review Date: 10/14/2012
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. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.
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