FTA-ABS

Alternative names
Fluorescent treponemal antibody absorption test

Definition

This blood test is used to detect antibodies directed specifically to the bacteria that cause syphilis, Treponema pallidum.

This test is used routinely to confirm whether a positive screening test for syphilis reflects true infection with syphilis.

How the test is performed

Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood).

A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test

No special preparation is necessary.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:

     
  • Infant test or procedure preparation (birth to 1 year)  
  • Toddler test or procedure preparation (1 to 3 years)  
  • Preschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

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 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 non-reactive result indicates no current or past infection with syphilis.

What abnormal results mean

A positive FTA-ABS usually indicates infection with syphilis. This test will remain positive for life even if an individual has received appropriate treatment.

Other illnesses such as yaws and pinta may also result in positive FTA-ABS results.

What the risks are

     
  • Excessive bleeding  
  • Fainting or feeling light-headed  
  • Hematoma (blood accumulating under the skin)  
  • Infection (a slight risk any time the skin is broken)  
  • Multiple punctures to locate veins

Special considerations
FTA-ABS will remain positive for life even if syphilis has been adequately treated. Therefore, it cannot be used to monitor the treatment of syphilis.

Johns Hopkins patient information

Last revised: December 3, 2012
by Martin A. Harms, M.D.

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