Skip Navigation LinksHome > January 2014 - Volume 41 - Issue 1 > Improved Reverse Screening Algorithm for Treponema pallidum...
Sexually Transmitted Diseases:
doi: 10.1097/OLQ.0000000000000066
Original Study

Improved Reverse Screening Algorithm for Treponema pallidum Antibody Using Signal-to-Cutoff Ratios from Chemiluminescence Microparticle Immunoassay

Dai, Shuqin MD, PhD*†; Chi, Peidong MMed*†; Lin, Yuehao BM*†; Zheng, Xin MMed*†; Liu, Wen MMed*†; Zhang, Jingping MD*†; Zeng, Qiuyao BM*†; Wu, Xingping BM*†; Liu, Wanli MD*†; Wang, Junye MD, PhD*‡

Supplemental Author Material
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Abstract

Background

The widespread reverse syphilis screening algorithm involves 1 more treponemal test than the traditional screening algorithm, resulting in increased medical costs. In the first screening step of the algorithm, a chemiluminescence microparticle immunoassay is used to detect Treponema pallidum (TP) antibody on the basis of signal-to-cutoff (S/CO) ratios. We hypothesized that by analyzing S/CO ratios, we could determine a strategy to reduce unnecessary confirmatory testing.

Methods

The ARCHITECT Syphilis TP assay using the chemiluminescence microparticle immunoassay was used as a syphilis screening test, and all reactive results were followed up with a toluidine red unheated serum test (TRUST) and a TP particle agglutination (TPPA) assay. We evaluated the S/CO ratios of 319 reactive samples of a total of 8980 that were included in the screening tests. A receiver operating characteristic curve was used to determine the optimal S/CO ratio to predict confirmatory TPPA results.

Results

When the S/CO ratio was 9.9 or greater, the specificity and positive predictive value were both determined to be 100.0%. All samples (194/194) with S/CO ratios of 9.9 or greater, even with negative results for TRUST, were confirmed to be positive for treponemal antibody.

Conclusions

A sample with an S/CO ratio of 9.9 or greater in initial screening does not need an extra confirmatory TPPA test, although the sample has a negative result for TRUST. We propose a potentially cost-effective reverse screening algorithm, obviating the need for the secondary treponemal testing in 65.2% of the screening-reactive samples.

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