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What is Fluorescent Treponemal Antibody Absorption (FTA-Abs) test?

The fluorescent treponemal antibody absorption (FTA-Abs) test is a blood test that looks for the presence of antibodies to the bacteria Treponema pallidum - the causative agent for syphilis - in the body. Syphilis is a sexually transmitted disease that spreads through direct contact with an infected person. It manifests in the form of chancre (small, painless sores) that show up on the genital region near the anus and mouth and eventually develop into rashes and flu-like symptoms. In the final stage, the heart, brain, bones, joints, lungs and almost all other organs can be affected. An infected pregnant lady can pass the disease to the foetus.

Antibodies are special proteins made by the immune system when it detects harmful substances such as bacteria, virus and fungus. Specific antibodies are made against specific microbes. Thus, people suffering from syphilis will have specific antibodies against the bacteria T. pallidum.

  1. Why is a Fluorescent Treponemal Antibody Absorption (FTA-Abs) test performed?
  2. How do you prepare for a Fluorescent Treponemal Antibody Absorption (FTA-Abs) test?
  3. How is a Fluorescent Treponemal Antibody Absorption (FTA-Abs) test performed?
  4. What do Fluorescent Treponemal Antibody Absorption (FTA-Abs) test results mean?

Your healthcare provider will order an FTA-Abs test if you have the following symptoms and signs of syphilis:

FTA-Abs test may also be recommended in the following situations:

  • If your partner has been diagnosed with syphilis
  • If you have been diagnosed with any other STD such as gonorrhoea
  • During the first and third trimesters of pregnancy and after delivery
  • If you recently had unprotected sex with multiple partners 
  • If you are a man who engages in sexual activity with other men
  • If you have HIV

FTA-Abs test is generally considered a confirmatory test for syphilis. It may be ordered if you get a positive result in screening tests, such as rapid plasma reagin and venereal disease research laboratory tests.

You are not required to perform anything special to prepare for this test. Let the healthcare provider know if you are consuming any medicines, including non-prescription and illegal drugs, supplements and vitamins. Certain medications may interfere with the results of this test. However, do not discontinue any drug unless asked by the doctor. 

For this test, a doctor or laboratory technician will collect a small amount of blood from a vein in your arm - you may feel a slight prick. In case you are afraid of needles or blood, distract yourself by talking to someone or look away. 

After the test, the sample will be immediately sent to the laboratory for analysis.

Normal results:

Normal or negative results indicate that you do not have syphilis or never had the disease in the past. Usually, anti-treponemal antibodies take a few weeks to develop. If you are sure you have been infected, ask your doctor if you need a retest.

Abnormal results:

Abnormal or positive test results mean that your body has antibodies against T. pallidum bacteria and that you either have a syphilis infection or had one in the past. The results will be positive even if you had been previously diagnosed with syphilis and successfully treated for the disease.

Rarely, you may get a false-positive result, which means that you have some antibodies in your body but you do not have syphilis. This may occur if you have yaws (a chronic infection of the skin, bones and joints) or pinta (skin disease). Some women who have lupus may also show a false-positive result for this test.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. World Health Organization [Internet]. Geneva (SUI): World Health Organization; Yaws
  2. National Organisation of Rare Disorders [Internet]. Danbury, CT, U.S. Pinta
  3. American Pregnancy Association [internet]. Syphilis
  4. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2018. Syphilis
  5. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Rapid Plasma Reagin
  6. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2018. Tests for Brain, Spinal Cord, and Nerve Disorders
  7. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests
  8. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services; Syphilis - CDC Fact Sheet (Detailed)
  9. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; VDRL (CSF)
  10. National Institute of Allergies and Infectious diseases [internet]: National Institute of Health. US Department of Health and Human Services; Syphilis
  11. Tsang RSW, Radons SM, Morshed M. Laboratory diagnosis of syphilis: a survey to examine the range of tests used in Canada. Can J Infect Dis Med Microbiol. 2011;22(3):83-87. PMID: 22942884
  12. UFHealth [internet]: University of Florida; Syphilis
  13. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; Health Information. Syphilis Tests
  14. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Congenital syphilis
  15. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Syphilis
  16. National Health Service [internet]. UK; Blood Tests
  17. US Preventive Services Task Force (USPSTF), Bibbins-Domingo K, Grossman DC, et al. Screening for syphilis infection in nonpregnant adults and adolescents: US Preventive Services Task Force recommendation statement. JAMA. 2016;315(21):2321-2327. PMID: 27272583. PMID: 27272583
  18. Chernecky CC, Berger BJ. Fluorescent Treponemal Antibody-Absorbed Double-Stain (FTA-Abs DS) Test - Serum. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders. 2013. Pp:533,534.