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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*‡

Sexually Transmitted Diseases: January 2014 - Volume 41 - Issue 1 - p 29–34
doi: 10.1097/OLQ.0000000000000066
Original Study

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.

The reverse syphilis screening algorithm was improved by using signal to cutoff values from initial ARCHITECT Syphilis TP, obviating the need for confirmatory testing in 65.2% of the screening-reactive samples.

From the *State Key Laboratory of Oncology in South China and Departments of †Clinical Laboratory and ‡Thoracic Surgery, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong, China

S. Dai and P. Chi contributed equally to this work.

No potential conflicts of interest were disclosed.

Research funding: J. Wang received funding support from the Science and Technology Planning Project of Guangzhou, China (2010B031600066).

Correspondence: Junye Wang, PhD, State Key Laboratory of Oncology in South China, Department of Thoracic Surgery, Sun Yat-Sen University Cancer Center, 651 Dongfeng Rd E, Guangzhou 510060, People’s Republic of China. E-mail: wangjunye888@126.com. Wanli Liu is to be contacted at the State Key Laboratory of Oncology in South China, Department of Clinical Laboratory, Sun Yat-Sen University Cancer Center, 651 Dongfeng Rd E, Guangzhou 510060, People’s Republic of China. E-mail: liuwanliliu@126.com.

Received for publication April 25, 2013, and accepted October 21, 2013.

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