European Journal of Cardiovascular Medicine

Syphilis is a multisystem infection caused by spirochete bacterium Treponema pallidum subsp. pallidum. It is commonly sexually transmitted but can also be vertically transmitted during pregnancy, causing congenital syphilis. It also transmit by blood transfusion.[1]  The diagnosis is mainly based on clinical findings and serologic tests since the organism cannot be grown in vitro. The clinical manifestations of the disease are classified by stages: primary syphilis, secondary syphilis, latent syphilis, and late or tertiary syphilis, including neurosyphilis and cardiovascular syphilis.[2] Confirmation of the diagnosis is through serological testing. As no single test is able to diagnose active syphilis, a combination of treponemal and nontreponemal tests are used [3]. Serological test for syphilis consist of Treponemal and non Treponemal tests.  Treponemal tests detect antibody to T pallidum proteins. Nontreponemal tests detect antibodies directed against lipoidal antigens, damaged host cells, and possibly from treponemes.[2] Both tests are used to evaluate the infection and determine whether the disease is active. Wasserman reaction (WR), Rapid plasma reagin (RPR), Venereal disease research laboratory (VDRL), and Toluidine  red unheated serum test (TRUST) are among non-treponemal test. The Fluorescent treponemal antibody-absorption (FTA-Abs), Treponema pallidum haemagglutination assay (TPHA), Treponema pallidum passive particle agglutination assay (TPPA), Enzyme immunoassay (EIA)-based anti treponemal tests (enzyme linked immunosorbent assay (ELISA), chemiluminescence and the majority of commercially available point-of-care are included in group of treponemal tests.[4] These tests have been the main method for screening, diagnosis and monitoring of disease activity.

Study Design: Cross  Sectional  Study.

Study Setting and Study Period: - The Study was conducted in  (Sexually transmitted diseases) STD Outpatient department , at a Tertiary Care Hospital, Hyderabad from 05 February 2024 to 12 January 2025.

Study Population: Patients  attending STD clinic , presenting with symptoms and signs suggestive of Syphilis (genital ulcer, skin rash).

All consecutive blood samples were tested by RPR (Carbogen®, Tulip Diagnostics P Ltd., India), TPHA (Bio-Rad, Marnes-la-Coquette, France), FTA-Abs IgM and FTA-Abs IgG were performed at the Laboratory to detect syphilis. All the procedures were performed as per the manufacturers guidelines.

Statistical Analysis: The statistical test was performed using SPSS ver 20.0 program (IBM Coorporation, New York, USA). The agreement of syphilis RDT with RPR and TPHA were determined by kappa coefficient. We compared the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of syphilis RDT, RPR, and TPHA in reference to FTA-Abs as the gold standard. The sensitivity of syphilis RDT, RPR, and TPHA is the proportion of subjects with diseases/FTA-Abs positive who tested positive with syphilis  RDT, RPR, or TPHA. The specificity of syphilis RDT, RPR, and TPHA is the proportion of subjects without diseases/FTA-Abs negative who tested negative with syphilis  RDT, RPR, or TPHA. The PPV is the proportion of the subjects with positive syphilis RDT, RPR, or TPHA tests who have disease which were FTA-Abs positive. The NPV is the proportion of patients with negative syphilis RDT, RPR, or TPHA tests who do not have the disease which were FTA-Abs negative.

Among 164 samples obtained for syphilis diagnostic test, 43 samples were positive for RDT. The comparison of syphilis RDT with RPR, TPHA, FTA-Abs IgG and FTA-Abs IgM can be seen in Table 1.

Table No. 1 Syphilis RDT compared to RPR, TPHA, FTA-Abs Ig M and FTA Abs IgG

Table No.2 - RPR compared to FTA-Abs IgM and Ig G

Table No. 3 - TPHA compared to FTA-Abs IgM and Ig G

The use of syphilis RDT as screening test mandate a high sensitivity. In this study , the sensitivity of syphilis RDT to IgM FTA-Abs was 100%.

For syphilis diagnostic test, among 164 samples 43 samples were positive with syphilis RDT and the sensitivity of syphilis RDT was similar to RPR and TPHA(100.0%), the specificity was same as TPHA (78.06%), but lower than RPR (85.16%) when compared to FTA-Abs IgM. The sensitivity of syphilis RDT was 61.66% and specificity was 94.23% when compared to FTA-Abs IgG. The sensitivity of TPHA was 100.0% when compared to FTA-Abs IgM and 60.0% when compared to FTA-Abs IgG. The specificity of TPHA was 78.06% when compared to FTA-Abs IgM and 93.26% when compared to FTA-Abs IgG. The sensitivity of RPR was 100.0% when compared to FTA-Abs IgM and 48.33% when compared to FTA-Abs IgG. The specificity of RPR was 85.16% when compared to FTA-Abs IgM and 97.11% when compared to FTA-Abs IgG.

Syphilis RDT has good sensitivity for syphilis diagnosis when compared to FTA-Abs IgM, however the sensitivity is lower when compared to FTA-Abs IgG. Syphilis RDT gives similar results to TPHA as diagnostic tool for syphilis. A negative treponemal test likely indicates the absence of syphilis and no further testing is required.

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