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Original research
Designs of colonoscopic adenoma detection trials: more positive results with tandem than with parallel studies - an analysis of studies on imaging techniques and mechanical devices
  1. Katharina Zimmermann-Fraedrich1,
  2. Heiko Pohl2,
  3. Thomas Rösch1,
  4. Douglas K Rex3,
  5. Cesare Hassan4,
  6. Evelien Dekker5,
  7. Michal Filip Kaminski6,
  8. Michael Bretthauer7,8,
  9. Jocelyn de Heer1,
  10. Yuki Werner1,
  11. Guido Schachschal1,
  12. Stefan Groth9
  1. 1 Interdisciplinary Endoscopy, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  2. 2 Gastroenterology and Hepatology, VA White River Junction/Dartmout Hitchcock Medical Center, White River Junction, Vermont, USA
  3. 3 Division of Gastroenterology and Hepatology, Indiana University School of Medicine, Indiana University Hospital, Indianapolis, Indiana, USA
  4. 4 Gastroenterology Unit, Nuovo Regina Margherita Hospital, Rome, Italy
  5. 5 Department of Gastroenterology and Hepatology, Amsterdam University Medical Centers, Amsterdam, The Netherlands
  6. 6 Department of Gastroenterology, Hepatology and Oncology, Center for Postgraduate Medical Education, Warsaw, Poland
  7. 7 Clinical Effectiveness Research Group, Department of Health Management and Health Economics, University of Oslo, Oslo, Norway
  8. 8 Section of Gastroenterology, Department of Transplantation Medicine, Oslo University Hospital, Oslo, Norway
  9. 9 Gastrozentrum Hirslanden, Zurich, Switzerland
  1. Correspondence to Dr Thomas Rösch, Interdisciplinary Endoscopy, University Hospital Hamburg-Eppendorf, Hamburg 20246, Germany; t.roesch{at}


Background and aims Adenoma detection rate (ADR) has been shown to correlate with interval cancers after screening colonoscopy and is commonly used as surrogate parameter for its outcome quality. ADR improvements by various techniques have been studied in randomised trials using either parallel or tandem methodololgy.

Methods A systematic literature search was done on randomised trials (full papers, English language) on tandem or parallel studies using either adenoma miss rates (AMR) or ADR as main outcome to test different novel technologies on imaging (new endoscope generation, narrow band imaging, iScan, Fujinon intelligent chromoendoscopy/blue laser imaging and wide angle scopes) and mechanical devices (transparent caps, endocuff, endorings and balloons). Available meta analyses were also screened for randomised studies.

Results Overall, 24 randomised tandem trials with AMR (variable definitions and methodology) and 42 parallel studies using ADR (homogeneous methodology) as primary outcome were included. Significant differences in favour of the new method were found in 66.7% of tandem studies (8222 patients) but in only 23.8% of parallel studies (28 059 patients), with higher rates of positive studies for mechanical devices than for imaging methods. In a random-effects model, small absolute risk differences were found, but these were double in magnitude for tandem as compared with parallel studies (imaging: tandem 0.04 (0.01, 0.07), parallel 0.02 (0.00, 0.04); mechanical devices: tandem 0.08 (0.00, 0.15), parallel 0.04 (0.01, 0.07)). Nevertheless, 94.2% of missed adenomas in the tandem studies were small (<1 cm) and/or non-advanced.

Conclusions A tandem study is more likely to yield positive results than a simple parallel trial; this may be due to the use of different parameters, variable definitions and methodology, and perhaps also a higher likelihood of bias. Therefore, we suggest to accept positive results of tandem studies only if accompanied by positive results from parallel trials.

  • colonic adenomas
  • colonoscopy

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  • Contributors KZF, JdH, GS and SG performed the literature analysis which was screened and selected by KZF and TR. The analyses were done and controlled by KZF, JdH, GS, SG, TR, YW, MB and HP. HP performed the statistical analysis and produced the figures. All authors had access to the data of the analyses and had reviewed and approved the final manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data relevant to the study are included in the article or uploaded as online supplementary information. This is a literature analysis where the papers have been published and are summarised in detail in the suppl appendix.