Rates and determinants of informed consent: A case study of an international thromboprophylaxis trial

Orla M. Smith, Ellen McDonald, Nicole Zytaruk, Denise Foster, Andrea Matte, France Clarke, Laurie Meade, Nicole O'Callaghan, Shirley Vallance, Pauline Galt, Dorrilyn Rajbhandari, Marcelo Rocha, Sangeeta Mehta, Niall D. Ferguson, Richard Hall, Robert Fowler, Karen Burns, Ismael Qushmaq, Marlies Ostermann, Diane Heels-AnsdellDeborah Cook

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18 Citations (Scopus)


Background: Successful completion of randomized trials depends upon efficiently and ethically screening patients and obtaining informed consent. Awareness of modifiable barriers to obtaining consent may inform ongoing and future trials. Objective: The objective of this study is to describe and examine determinants of consent rates in an international heparin thromboprophylaxis trial (Prophylaxis for ThromboEmbolism in Critical Care Trial, clinicaltrials.gov NCT00182143). Design: Throughout the 4-year trial, research personnel approached eligible critically ill patients or their substitute decision makers for informed consent. Whether consent was obtained or declined was documented daily. Setting: The trial was conducted in 67 centers in 6 countries. Measurements and main results: A total of 3764 patients were randomized. The overall consent rate was 82.2% (range, 50%-100%) across participating centers. Consent was obtained from substitute decision makers and patients in 90.1% and 9.9% of cases, respectively. Five factors were independently associated with consent rates. Research coordinators with more experience achieved higher consent rates (odds ratio [OR], 3.43; 95% confidence interval, 2.42-4.86; P < .001 for those with > 10 years of experience). Consent rates were higher in smaller intensive care units with less than 15 beds compared with intensive care units with 15 to 20 beds, 21 to 25 beds, and greater than 25 beds (all ORs, < 0.5; P < .001) and were higher in centers with more than 1 full-time research staff (OR, 1.95; 95% confidence interval, 1.28-2.99; P < .001). Consent rates were lower in centers affiliated with the Canadian Critical Care Trials Group or the Australian and New Zealand Intensive Care Society Clinical Trials Group compared with other centers (OR, 0.57; 95% confidence interval, 0.42-0.77; P < .001). Finally, consent rates were highest during the pilot trial, lowest during the initiation of the full trial, and increased over years of recruitment (P < .001). Conclusions: Characteristics of study centers, research infrastructure, and experience were important factors associated with successfully procuring informed consent to participate in this thromboprophylaxis trial.

Original languageEnglish
Pages (from-to)28-39
Number of pages12
JournalJournal of Critical Care
Issue number1
Publication statusPublished - Feb 2013
Externally publishedYes


  • Clinical research
  • Critical care
  • Informed consent
  • Intensive care
  • Randomized trials
  • Studies

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