SYPGR - Clinical: Syphilis IgG Antibody with Reflex, Serum

Test Catalog

Test Name

Test ID: SYPGR    
Syphilis IgG Antibody with Reflex, Serum

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

Aids in the diagnosis of active Treponema pallidum infection


Routine prenatal screening

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

If syphilis IgG is positive, then rapid plasma reagin (RPR) will be performed at an additional charge.


If RPR is positive, then RPR titer will be performed at an additional charge.


If RPR is negative, then syphilis antibody 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 nontreponemal screening test, such as the rapid plasma reagin (RPR) or the venereal disease research laboratory (VDRL) tests. Because these tests measure the host's antibody response to nontreponemal 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.


Recently, enzyme immunoassays (EIA) and multiplex flow immunoassays (MFI) were introduced to assess serologic response to T pallidum. The Bio-Rad BioPlex Syphilis IgG assay is an example of MFI technology, which utilizes specific, treponemal antigens coated on microspheres for the detection of IgG-class antibodies to T pallidum. The BioPlex Syphilis IgG assay is highly sensitive and specific (see Supportive Data), and allows for an objective interpretation of results. Due to several factors including the low prevalence of syphilis in the United States, the increased specificity of treponemal assays, and the objective interpretation of MFI and EIA technology, initial serologic testing by a treponemal-specific assay (eg, EIA or MFI) is now commonly performed in clinical laboratories. Specimens testing positive by the treponemal-specific assay are then tested by RPR to provide supplementary serologic data, as well as to provide an indication of the patient's disease state and history of treatment.


During early primary syphilis, patients may present with nonspecific clinical findings and serology tests may be negative. As the disease progresses into the secondary phase, IgG-class antibodies to T pallidum reach peak titers, and may persist indefinitely regardless of the disease state or prior therapy. 


For prenatal syphilis screening, the IgG test is recommended. IgM testing should not be performed during routine pregnancy screening unless clinically indicated.


T pallidum IgG antibodies persist indefinitely, regardless of whether the patient has been treated or not. To determine if a patient has been treated for syphilis, the RPR test is performed. If the RPR is positive, the results may suggest active, untreated syphilis. In contract, a positive syphilis screening test and a negative RPR most likely suggest past, successfully treated syphilis.

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.


Interpretation Provides information to assist in interpretation of the test results

Syphilis screening at Mayo Clinic is performed by using the reverse algorithm, which first tests sera for Treponema pallidum specific IgG antibodies using an automated multiplex flow immunoassay (MFI). A positive IgG treponemal test suggests infection with T pallidum at some point in the past, but does not distinguish between treated and untreated infections. This is because treponemal tests (eg, EIA, MFI, or fluorescent treponemal antibody-absorbed: FTA-ABS) may remain reactive for life, even following adequate therapy. Therefore, the results of a nontreponemal assay, such as rapid plasma reagin (RPR), are needed to provide information on a patient's disease state and history of therapy.


In some patients, the results of the treponemal screening test (syphilis IgG) and RPR may be discordant (eg, syphilis IgG positive and RPR negative). To discriminate between a falsely reactive screening result and past syphilis, CDC recommends performing a second treponemal-specific antibody test using a method that is different from the initial screen test (eg, T pallidum particle agglutination: TP-PA).(1)


In the setting of a positive syphilis IgG 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 screening result and a negative RPR, a negative TP-PA result is most consistent with a falsely reactive syphilis IgG 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






Unknown history of syphilis




No serologic evidence of syphilis

None, unless clinically indicated (eg, early 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

Unknown history of syphilis




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

Historical and clinical evaluation required

Known history of syphilis



Reactive or N/A

Past, successfully treated syphilis


CIA, chemiluminescence immunoassay; EIA, enzyme immunoassay; MFI, multiplex flow immunoassay; N/A, not applicable; RPR, rapid plasma reagin; TP-PA, Treponema pallidum particle agglutination.              

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

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


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 (MFI) and 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.

Supportive Data

To evaluate the accuracy of the BioPlex Syphilis IgG assay, 1,008 consecutive, unique serum specimens submitted for routine syphilis IgG testing by EIA were also tested on the BioPlex 2200. Specimens showing discrepant results were repeatedly tested by both methods, and also tested by Treponema pallidum-particle agglutination (TP-PA). The BioPlex 2200 Syphilis IgG assay correctly identified 77 (98.7%) of the 78 specimens that were positive by EIA. The EIA-positive, BioPlex-negative specimen was shown to be truly negative by TP-PA and repeat EIA. In addition, the BioPlex assay correctly identified 916 (98.5%) of the 930 specimens that were negative by EIA. Among the 14 BioPlex-positive, EIA-negative specimens, 8 were shown to be truly positive by TP-PA (see Table 2). The BioPlex Syphilis IgG assay demonstrated an adjusted sensitivity and specificity of 100% and 99.4%, respectively.


Table 2. Comparison of the Bio-Rad Syphilis IgG Assay and the Trep-Chek EIA among Prospective Serum Specimens (n=1,008):

EIA Positive

EIA Negative


BioPlex Positive




BioPlex Negative








a. 8/14 positive by TP-PA upon follow-up testing

b. Negative by EIA upon repeat testing

Sensitivity: 77/78 =98.7% (95% Confidence intervals: 92.4%, 99.9%)

Specificity: 916/930 =98.5% (95% Confidence intervals: 97.5%, 99.1%)


To evaluate the accuracy of the TP-PA assay, it was compared to the BioPlex 2200 syphilis IgG MFI assay using 1,200 serum specimens (1,100 prospective and 100 previously characterized sera). The results are summarized in Table 3:


Table 3. Comparison of the BioPlex 2200 syphilis IgG and TP-PA assays using serum samples (n =1,200): 



BioPlex syphilis IgG MFI





No result

Fujirebio TP-PA














Sensitivity =90.18%; (95% confidence interval, 83.15%- 94.61%)

Specificity =99.6%; (95% confidence interval, 99.0%- 99.9%)

Overall percent agreement =98.7%; (95% confidence interval, 96.3%- 100%)


All discrepant samples tested negative by RPR.

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

1. CDC. Discordant results from reverse sequence syphilis screening - five laboratories, United States, 2006-2010. Morb Mortal WKLY Rep 2011;60(5):133-137

2. Tramont EC: Treponema pallidum (Syphilis). In Principles and Practice of Infectious Diseases. Fifth edition. Edited by GL Mandell, JE Bennet, R Dolin. New York, Churchill Livingstone, 2000, pp 2474-2491

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 and Forms Library of PDFs including pertinent information and consent forms, specimen collection and preparation information, test algorithms, and other information pertinent to test