FTA-ABS test

Definition

The FTA-ABS test is a blood test to detect antibodies to the bacteria Treponema pallidum, which causes syphilis.

This test is used to confirm whether a positive screening test for syphilis means there is a true infection.

Alternative Names

Fluorescent treponemal antibody absorption test

How the test is performed

A blood sample is needed. For information on how this is done, see: Venipuncture

How to prepare for the test

No special preparation is necessary.

How the test will feel

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

Why the test is performed

This test is routinely done to confirm whether a positive screening test for syphilis (either VDRL or RPR) means you have a current syphilis infection.

It may also be done when other syphilis tests are negative, to rule out a possible false-negative result.

Normal Values

A negative or nonreactive result means there you do not have a current or past infection with syphilis.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

A positive FTA-ABS is usually a sign of a syphilis infection. This test result will remain positive for life even if syphilis has been adequately treated. Therefore, it cannot be used to monitor the treatment of syphilis.

Other illnesses such as yaws and pinta may also result in positive FTA-ABS results. Occasionally there can be a false positive result, most often in women with lupus.

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)

Special considerations

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References

Tramont EC. Treponema pallidum (syphilis). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 238.