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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

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

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 used routinely to confirm whether a positive screening test for syphilis (either VDRL or RPR ) reflects true infection with syphilis. It may also be done when either primary or tertiary syphilis are suspected and the initial screening tests are negative, because screening tests during these stages of syphilis may be falsely negative.

Normal Values

A negative or nonreactive result means there is no current or past infection with syphilis.

What abnormal results mean

A positive FTA-ABS usually indicates infection with syphilis. 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)

References

Hook EW III. Syphilis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 340.

Centers for Disease Control and Prevention, Workowski KA, Berman SM. Diseases characterized by genital ulcers. Sexually transmitted diseases treatment guidelines 2006. MMWR Morb Mortal Wkly Rep. 2006 Aug 4;55(RR-11):14-30.

Eckert LO, Lentz GM. Infections of the lower genital tract: vulva, vagina, cervix, toxic shock syndrome, HIV infections. In: Katz VL, Lentz GM, Lobo RA, Gershenson DM, eds. Comprehensive Gynecology. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2007:chap 22.


Review Date: 7/27/2009
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; and Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Redmond, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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