Background:
Colorectal cancer/CRC-Screening has the potential for both early detection and prevention. There are several candidates for first-line screening tests. Colonoscopy is a possible first-line test and plays a key role for further diagnosis and intervention as the final common pathway of all first-line screening-tests. For a screening intervention colonoscopy is very invasive and holds the small risk of serious complications.

Methods:
Starting from a recent overview by the "Australian Institute for Health and Welfare/AIHW", guidelines and position papers on quality assurance in CRC-screening with a particular focus on screening-colonoscopies were searched. Apart from the European Guidelines for Quality Assurance in Colorectal Screening and Diagnosis (2010) additional position papers were identified and the major stakeholders in Austria contacted.

Results:
Organized CRC-screening programs in Australia, England, Finland, France, Italy, Poland, Scotland and Slovenia are briefly presented. Quality assurance in the English program is outstanding. Germany mandates compulsory and comprehensive quality assurance of (opportunistic) screening-colonoscopies. In Austria quality assurance to this degree is only safeguarded in the province of Vorarlberg. Organized screening-programs in Ireland, the Netherlands and Norway are in their initial stages. The comprehensive, and coordinated pilot-study based planning and the institutional groundwork done in the Netherlands can be taken as an example to learn from.
Participation rates effectively observed in real life CRC-screening programs vary considerably. They tend to be higher with FOBT (gFOBT 37-66%, iFOBT 17-48%) than with flexible sigmoidoscopy (24%) and colonoscopy (18-24%).
Position papers of key Austrian stakeholders emphasize the importance of quality assurance in CRC-screening and in screening-colonoscopy in particular. For quality assurance of screening-colonoscopy an established range of quality measures is available. The comprehensiveness of indicators and the defined target ranges of measures endorsed by national and international institutions vary however. Existing voluntary quality assurance measures of screening-colonoscopy in Austria (ÖGGH certificate) are not among the most stringent when compared with organized programs in England and the Netherlands or with the recommendations of one Spanish medical society.

Discussion:
The emerging evidence on effectiveness of CRC-screening allows to tentatively infer that all CRC-screening strategies might prove to have similar effect sizes when introduced into programmatic screening-practice. Quality assurance and participation rates may be of key importance for realizing potential net health gains from CRC-screening instead.
Even if quality assurance is made mandatory in the context of opportunistic screening, it cannot match the stringent and comprehensive quality focus of organized screening-programs. The publication of the European Guidelines for Quality Assurance in Colorectal Cancer Screening and Diagnosis have encouraged the dynamic towards establishing organized and quality assured CRC-screening programs.
Examples of how to plan and organize quality assurance in population-based CRC-screening programs is available. Interesting models to learn from can, for instance, be found in England, the Netherlands and in Norway.