title: Incidence and risk factors for the prozone phenomenon in serologic testing for syphilis in a large cohort.
abstract: BACKGROUND
  The prozone phenomenon is known to be associated with high antibody titers; other associations, such as host factors, have not been elucidated.
  
  
  METHODS
  A retrospective analysis was conducted to evaluate the incidence of the prozone phenomenon of the syphilis rapid plasma reagin (RPR) test among 46 856 clinical samples, between June 2010 and June 2013. Logistic regression was used to analyze the risk factors of the prozone phenomenon.
  
  
  RESULTS
  Our results showed that the incidence of the prozone phenomenon was low (0.83%) and could occur during any clinical phase, particularly during primary and secondary syphilis. Pregnancy and neurosyphilis were associated with the prozone phenomenon; sex, age, and whether the patient had been treated were not. The results also revealed that the prozone phenomenon not only occurred in patients with a high titer but also could occur in patients with a moderate/low titer. In fact, almost 31% of the patients with the prozone phenomenon had titers ≤1:16.
  
  
  CONCLUSIONS
  The prozone phenomenon in the RPR test was associated with the phase of syphilis, pregnancy, and neurosyphilis as well as a range of RPR titers between 1:8 and 1:512. This latter finding is in contrast to previous reports that the prozone phenomenon is associated with very high RPR titers.
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University Xiamen Zhongshan Hospital, Fujian Medical University Xiamen Zhongshan Hospital, Fujian University of Traditional Chinese Medicine, Xiamen.
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Liu
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University Xiamen Zhongshan Hospital, Fujian University of Traditional Chinese Medicine, Xiamen.
authors.forename: Li-Rong
authors.initials: LR
authors.lastname: Lin
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University.
authors.forename: Man-Li
authors.initials: ML
authors.lastname: Tong
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University.
authors.forename: Hui-Lin
authors.initials: HL
authors.lastname: Zhang
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University.
authors.forename: Song-Jie
authors.initials: SJ
authors.lastname: Huang
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University.
authors.forename: Yu-Yan
authors.initials: YY
authors.lastname: Chen
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University.
authors.forename: Xiao-Jing
authors.initials: XJ
authors.lastname: Guo
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University.
authors.forename: Ya
authors.initials: Y
authors.lastname: Xi
authors.affiliation: Department of Chemistry and Biology, College of Science, National University of Defense and Technology, Changsha, China.
authors.forename: Long
authors.initials: L
authors.lastname: Liu
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs.
authors.forename: Fu-Yi
authors.initials: FY
authors.lastname: Chen
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University.
authors.forename: Ya-Feng
authors.initials: YF
authors.lastname: Zhang
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University.
authors.forename: Qiao
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Zhongshan Hospital, Medical College of Xiamen University Xiamen Zhongshan Hospital, Fujian University of Traditional Chinese Medicine, Xiamen ShenZhen Research Institute of Xiamen University, ShenZhen, China.
authors.forename: Tian-Ci
authors.initials: TC
authors.lastname: Yang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000372:Agglutination Tests; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D011935:Reagins / Q000097:blood*; D012189:Retrospective Studies; D012307:Risk Factors; D013587:Syphilis / Q000175:diagnosis*; D013588:Syphilis Serodiagnosis; D055815:Young Adult
chemical_list: D011935:Reagins
keywords: prozone phenomenon; rapid plasma reagin; serologic test; syphilis