Ann Lab Med 2017; 37(6): 511-515  
Comparison of Traditional and Reverse Syphilis Screening Algorithms in Medical Health Checkups
Eun-Hee Nah, M.D.¹, Seon Cho, M.S.1, Suyoung Kim, M.S.1, Han-Ik Cho, M.D.², and Jong-Yil Chai, M.D.3
Department of Laboratory Medicine and Health Promotion Research Institute1, Korea Association of Health Promotion, Seoul; MEDIcheck LAB2, Korea Association of Health Promotion, Cheongju; Institute of Parasitic Diseases3, Korea Association of Health Promotion, Seoul, Korea
Correspondence to: Eun-Hee Nah
Department of Laboratory Medicine and Health Promotion Research Institute, Korea Association of Health Promotion, 350 Hwagok-ro, Gangseo-gu, Seoul 07653, Korea
Tel: +82-2-2600-0107 Fax: +82-2-2690-4915 E-mail: cellonah@hanmail.net
Received: January 12, 2017; Revised: March 2, 2017; Accepted: July 3, 2017; Published online: November 1, 2017.
© The Korean Society for Laboratory Medicine. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background: The syphilis diagnostic algorithms applied in different countries vary significantly depending on the local syphilis epidemiology and other considerations, including the expected workload, the need for automation in the laboratory and budget factors. This study was performed to investigate the efficacy of traditional and reverse syphilis diagnostic algorithms during general health checkups.
Methods: In total, 1,000 blood specimens were obtained from 908 men and 92 women during their regular health checkups. Traditional screening and reverse screening were applied to the same specimens using automatic rapid plasma regain (RPR) and Treponema pallidum latex agglutination (TPLA) tests, respectively. Specimens that were reverse algorithm (TPLA) reactive, were subjected to a second treponemal test performed by using the chemiluminescent microparticle immunoassay (CMIA).
Results: Of the 1,000 specimens tested, 68 (6.8%) were reactive by reverse screening (TPLA) compared with 11 (1.1%) by traditional screening (RPR). The traditional algorithm failed to detect 48 specimens [TPLA(+)/RPR(-)/CMIA(+)]. The median TPLA cutoff index (COI) was higher in CMIA-reactive cases than in CMIA-nonreactive cases (90.5 vs 12.5 U).
Conclusions: The reverse screening algorithm could detect the subjects with possible latent syphilis who were not detected by the traditional algorithm. Those individuals could be provided with opportunities for evaluating syphilis during their health checkups. The COI values of the initial TPLA test may be helpful in excluding false-positive TPLA test results in the reverse algorithm.
Keywords: Syphilis, Treponema pallidum, Rapid plasma regain (RPR), Treponema pallidum latex agglutination, Chemiluminescent microparticle immunoassay, Algorithm


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