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Randomised controlled trial on whether advance knowledge of prostate-specific antigen testing improves participant reporting of unprotected sex
  1. Sarah C Thomsen1,
  2. Maria F Gallo1,
  3. Wilkister Ombidi2,
  4. Zablon Omungo3,
  5. Barbara Janowitz1,
  6. Mark Hawken2,
  7. Heidi Tucker1,
  8. Emelita L Wong1,
  9. Marcia M Hobbs4
  1. 1Family Health International, Research Triangle Park, North Carolina, USA
  2. 2International Centre for Reproductive Health, Mombasa, Kenya
  3. 3Family Health International, Nairobi, Kenya
  4. 4University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
  1. Correspondence to:
 Dr M F Gallo
 Centers for Disease Control and Prevention, Division of Reproductive Health, 4770 Buford Highway, NE, MS K-34, Atlanta, GA 30341, USA; mgallo{at}


Objectives: To determine whether the process of informing research participants that they would be tested for the presence of a biological marker of semen exposure would reduce bias in their reports of unprotected sex.

Methods: A randomised trial of 210 female sex workers from Mombasa, Kenya, was conducted, where half the group had advance knowledge (via the request for informed consent) that they would be tested for prostate-specific antigen (PSA) in their vaginal fluid before they reported on sex and condom use for the past 48 h. The other half were invited to participate (via additional informed consent) in the test for PSA after they had already consented to be questioned and reported on these sexual behaviours. A trained nurse instructed participants to self-swab to collect vaginal fluid specimens, which were tested for PSA using ELISA.

Results: Reporting of unprotected sex did not differ between those with advance knowledge of the test for PSA and those without this knowledge (14.3% v 11.4%, respectively; p = 0.27). Surprisingly, more women with advance knowledge (15.8%) had discrepant self reports and PSA results than women without advance knowledge (9.1%); however, the difference was not statistically significant (OR 1.9; 95% CI 0.8 to 4.5).

Conclusions: Knowing that one’s answers to a questionnaire could be verified with a biological marker of semen exposure did not make respondents more likely to report unprotected sex.

  • PSA, prostate-specific antigen

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  • Competing interests: None.

  • Contributors: The idea for the study came from BJ, who also reviewed analyses and the text. SCT designed and oversaw the conduct of the study and, along with, MFG, who coordinated the PSA portion of the study, wrote the bulk of the text. MH was the principal investigator and WO was the research coordinator. ZO conducted training and monitored the study. ELW designed and approved all statistical analyses, which were carried out by HT. MMH oversaw all laboratory procedures. All authors contributed to the writing of the manuscript and have reviewed and approved its content.

  • Published Online First 29 November 2006