Sign In
Labcorp Oklahoma, Inc.
Test Directory


Non-Treponemal Antibody

Test Number: 5500605
Revision Date 08/01/2022
Test Name Methodology LOINC Code
Non-Treponemal Antibody
Complement Fixation 31147-2 
Specimen Specimen Volume (min) Specimen Type Specimen Container Transport Environment
Preferred 1 mL Serum Clot Activator SST Refrigerated
Testing Schedule Mon-Fri 
Expected TAT 3 Days  
Clinical Use This Non-Treponemal Antibody (RPR) is the Reflex Confirmation test to the Syphilis Antibody Screen. This is also used to check the progress of treatment for active syphilis patients.

Interpretation for the Non-Treponemal Antibody Assay
The Non-Treponemal Antibody Assay, referred to as the RPR assay in past years, is NOT the best test for screening for Syphilis because of the potential for false positive results which most often occur whenever there is a strong immunologic stimulus (e.g. pregnancy, IV drug abuse, dialysis, acute bacterial or viral infection, untreated HIV infection, etc.). The preferred test for screening is the Syphilis Antibody Screening Test (Syp Ab; 5500707) which is an algorithm testing for the Treponemal Antibody and if positive reflexes to the Non-Treponemal Antibody (RPR; 550605) which will provide a titer if positive. A third test in the algorithm is a Treponema Pallidum Particle Agglutination assay (TPPA; 5501065) that will only be performed to further evaluate inconclusive results.

The Non-Treponemal Antibody Assay (RPR) is valuable for confirming an active infection when the Treponemal Antibody (Syp Ab) assay is positive, to assess the success of treatment and to determine the presence of a Syphilis infection in a newborn. The Non-Treponemal Antibody Assay (RPR) should become nonreactive 1 year after successful therapy in a primary Syphilis infection and 2 years in a secondary Syphilis infection; most patients with late Syphilis will be nonreactive by the fifth year after successful therapy. The Non-Treponemal Antibody Assay (RPR) should have a significant decrease of fourfold as early as 3-6 months, following successful treatment. The Non-Treponemal Antibody Assay (RPR) is the only assay necessary for evaluation upon reinfection since the Treponemal Antibody Assay (Syp Ab) will be positive for decades if not for life in an individual who has been previously infected. However, in untreated disease the titers will reach their highest titer during the secondary and early latent stages and decline thereafter, usually to less than 1:4. Over time, at least 25% of untreated persons become Non-Treponemal Antibody (RPR) nonreactive or serofast at a titer less than 1:4.

In newborns, the Non-Treponemal Antibody (RPR) is the test of choice because the overwhelming majority of the Ig anti-Treponemal Antibody (Syp Ab) in the newborn is maternal antibody. Detectable levels of maternal IgG anti-Treponemal Antibody (Syp Ab) can be detected in the baby’s serum up to 15-18 months. 
CPT Code(s) 86592
Lab Section Immunology - Serology