Test Catalog

Test ID: SYPHT    
Syphilis Total Antibody with Reflex, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Aiding in the diagnosis of recent or past Treponema pallidum infection


Routine prenatal screening


This test is not offered as a screening or confirmatory test for blood donor specimens.


This test is not useful for diagnosis of congenital syphilis.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

If the syphilis total antibody result is nonreactive, billing will be captured under SYPNB.


If the syphilis total antibody result is reactive or equivocal, then the rapid plasma reagin (RPR) screen will be performed, and billing will be captured under SYPPB.


If the RPR screen is reactive, then the RPR titer will be performed at an additional charge.


If the RPR screen is nonreactive, then syphilis antibody Treponema pallidum particle agglutination testing will be performed at an additional charge.


See Syphilis Serology Algorithm in Special Instructions.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Syphilis is a disease caused by infection with the spirochete Treponema pallidum. The infection is systemic, and the disease is characterized by periods of latency. These features, together with the fact that T pallidum cannot be isolated in culture, mean that serologic techniques play a major role in the diagnosis and follow-up of treatment for syphilis.


Historically, the serologic testing algorithm for syphilis included an initial non-treponemal screening test, such as the rapid plasma reagin (RPR) or the VDRL tests. Because these tests measure the host's antibody response to non-treponemal antigens, they lack specificity. Therefore, a positive result by RPR or VDRL requires confirmation by a treponemal-specific test, such as the fluorescent treponemal antibody-absorbed (FTA-ABS) or microhemagglutination assay (MHA-TP). Although the FTA-ABS and MHA-TP are technically simple to perform, they are labor intensive and require subjective interpretation by testing personnel.


As an alternative to the traditional syphilis screening algorithm as described above, many laboratories utilize the reverse syphilis screening algorithm. This algorithm starts with an automated treponemal assay, such as an enzyme immunoassay and multiplex flow immunoassay (MFI), to detect antibodies specific to T pallidum. If the screening assay is positive, the sample is reflexed to a RPR assay, which, if positive, is reported with a titer and is indicative of active or recent syphilis infection. If the RPR is negative, the sample is reflexed to a second treponemal assay, such as the T pallidum particle agglutination (TP-PA) assay. If the TP-PA is positive, this would indicate previously treated or late stage syphilis infection. Alternatively, if the TP-PA is negative, the initial positive screen is interpreted as a false positive result.


Syphilis screening at Mayo Clinic is performed by using the reverse algorithm, which first tests sera for T pallidum specific IgG/IgM antibodies using an automated MFI. A positive treponemal test suggests infection with T pallidum but does not distinguish between recent or past, or treated and untreated infection. This is because treponemal tests may remain reactive for life, even following adequate therapy. Therefore, the results of a non-treponemal assay, such as RPR, are needed to provide information on a patient's disease state and history of therapy.(Table 1)


In some patients, the results of the treponemal screening test and RPR may be discordant (eg, syphilis IgG/IgM positive and RPR negative). To discriminate between a falsely reactive screening result and past syphilis, a second treponemal-specific antibody test is recommended using a method that is different from the initial screen test (eg, TP-PA).


In the setting of a positive syphilis IgG/IgM screening result and a negative RPR, a positive TP-PA result is consistent with either 1) past, successfully treated syphilis, 2) early syphilis with undetectable RPR titers, or 3) late/latent syphilis in patients who do not have a history of treatment for syphilis. Further historical evaluation is necessary to distinguish between these scenarios.(Table 1)


In the setting of a positive syphilis IgG/IgM screening result and a negative RPR, a negative TP-PA result is most consistent with a falsely reactive syphilis IgG/IgM screen.(Table 1) If syphilis remains clinically suspected, a second specimen should be submitted for testing.

Table 1. Interpretation and follow-up of reverse screening results:

Test and result

Patient history

Syphilis total antibody by MFI





Unknown history of syphilis




No serologic evidence of syphilis

None, unless clinically indicated (eg, early/acute/ primary syphilis)

Unknown history of syphilis




Untreated or recently treated syphilis

See CDC treatment guidelines 

Unknown history of syphilis




Probable false-positive screening test

No follow-up testing, unless clinically indicated (eg, acute/primary syphilis)

Unknown history of syphilis




Possible syphilis (eg, early or latent) or previously treated syphilis

Historical and clinical evaluation required

Unknown history of syphilis





Unknown history of syphilis

Known history of syphilis



Reactive or NA

Past, successfully treated syphilis


MFI - multiplex flow immunoassay

NA - not applicable

RPR - rapid plasma reagin

TP-PA -Treponema pallidum particle agglutination

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.













Reference values apply to all ages

Interpretation Provides information to assist in interpretation of the test results


No serologic evidence of infection to Treponema pallidum (syphilis). Repeat testing may be considered in patients with suspected acute or primary syphilis in 2 to 4 weeks.



Rapid plasma reagin (RPR) has been ordered to help distinguish between infection with T pallidum (syphilis) versus a falsely reactive treponemal antibody result.



RPR has been ordered to help distinguish between infection with T pallidum (syphilis) versus a falsely reactive treponemal antibody result.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Despite active syphilis, serologic tests may be negative in severely immunosuppressed patients such as those with AIDS.


In very early cases of primary syphilis, serology tests for syphilis may be negative.


In cases of untreated, late or latent syphilis, the result of rapid plasma reagin may be negative. However, the syphilis screening test multiplex flow immunoassay (MFI) and Treponema pallidum particle agglutination (TP-PA) should be positive. A thorough clinical and historical evaluation should be performed to determine if treatment for latent syphilis is required.


Results should be considered in the context of all available clinical and laboratory data.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Centers for Disease Control and Prevention (CDC): Discordant results from reverse sequence syphilis screening-five laboratories, United States, 2006-2010. MMWR Morb Mortal Wkly Rep. 2011;60(5):133-137

2. Radolf JD, Tramont EC, Salazar JC: Syphilis (Treponema pallidum). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Elsevier; 2020:2865-2892

3. Binnicker MJ, Jespersen DJ, Rollins LO: Direct comparison of the traditional and reverse syphilis screening algorithms in a population with a low prevalence of syphilis. J Clin Microbiol. 2012: Jan;50(1):148-150

Special Instructions Library of PDFs including pertinent information and forms related to the test