Incidence of the prozone phenomenon in syphilis serology

Obstet Gynecol. 1994 Oct;84(4):609-12.


Objective: To determine the rate of the prozone phenomenon in our patient population.

Methods: Sera from 4328 patients--3504 females (2065 pregnant, 1439 nonpregnant) and 824 males--were tested for syphilis by the rapid plasma reagin (RPR) test, and then rechecked with serial twofold dilutions of up to 16-fold to detect the prozone phenomenon. Chi-square analysis with Yates correction was used, with P < or = .05 considered significant.

Results: The total positivity rate in females was 6% (213 patients); 13% (27) of the positive tests were false-positive reactions as confirmed by a negative anti-treponemal antibody test. Only one prozone reaction was detected, in serum from a male subject, but it was not missed on initial screening.

Conclusion: The rate of prozone phenomenon is very low (95% confidence interval 0-0.4%), and routine serial dilutions are not cost effective.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chi-Square Distribution
  • False Positive Reactions
  • Female
  • Humans
  • Incidence
  • Indicator Dilution Techniques
  • Male
  • Mass Screening*
  • Pregnancy
  • Pregnancy Complications, Infectious / diagnosis*
  • Syphilis / diagnosis*
  • Syphilis Serodiagnosis / methods*