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What is an invasive procedure? A definition to inform study design, evidence synthesis and research tracking
  1. Sian Cousins1,
  2. Natalie S Blencowe1,2,
  3. Jane M Blazeby1,2
  1. 1 Centre for Surgical Research, Population Health Sciences, University of Bristol, Bristol, UK
  2. 2 Division of Surgery, Head and Neck, University Hospitals Bristol NHS Foundation Trust, Bristol, United Kingdom
  1. Correspondence to Dr Sian Cousins; sian.cousins{at}


Worldwide, there are at least 230 million invasive procedures performed annually and most of us will undergo several in our lifetime. There is therefore a need for high-quality evidence to underpin this clinical area. Currently, however, there is no widely accepted definition of an invasive procedure and the terms ‘surgery’ and ‘interventional procedure’ are characterised inconsistently. We propose a definition for invasive procedures which addresses the limitations of those currently available. Our definition was developed from an analysis of the 3946 papers from the last decade. A preliminary definition was created based on existing definitions and applied to a variety of papers reporting all types of procedures. This definition was continuously updated and applied iteratively to all articles. The definition has three key components: (1) method of access to the body, (2) instrumentation and (3) requirement for operator skill. It therefore encapsulates all types of invasive procedure regardless of the method of access to the body (incision, natural orifice or percutaneous access), and is relevant whatever the clinical discipline (eg, obstetric, cardiac, dental, interventional cardiology or radiology). Crucially, the definition excludes medicinal products, except where their administration occurs within an invasive procedure (and thereby involves operator skill). The application of a universal definition of an invasive procedure will (1) inform the selection of relevant methods for study design, (2) streamline evidence synthesis and (3) improve research tracking, helping to identify evidence gaps and direct research funds.

  • surgery
  • study design
  • evidence synthesis
  • research tracking
  • definitions
  • invasive procedures

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  • Contributors All authors are based in the Bristol Centre for Surgical Research, the Surgical Innovation theme of the Bristol Biomedical Research Centre (BRC) and the MRC ConDuCT-II (Collaboration and innovation in Difficult and Complex randomised controlled Trials In Invasive procedures) Hub for Trials Methodology Research. SC is a research fellow and NSB and JMB are academic surgeons (MRC Clinician Scientist and professor of surgery, respectively). JMB is an NIHR senior investigator. Repeated challenges in designing and conducting methodological and applied research including recurrent requests from other research groups for advice in this area have led to conceptualisation and writing of this article. SC, NSB and JMB all contributed to the development of the manuscript and approved its final version. JMB is the guarantor.

  • Funding This study was supported by the MRC ConDuCT-II (Collaboration and innovation in Difficult and Complex randomised controlled Trials In Invasive procedures) Hub for Trials Methodology Research and the NIHR Biomedical Research Centre at University Hospitals Bristol NHS Foundation Trust and the University of Bristol. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the National Institute for Health Research or the Department of Health and Social Care.

  • Competing interests None declared.

  • Patient consent for publication Not required.

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