Discussion
The present large prospective study focused on the factors that are responsible for highly variable adenoma detection rates. For the first time, we used advanced statistical modelling that takes the cluster structure of the data into account to simultaneously examine the factors that are related to patients and the factors that are related to colonoscopists and their instruments; thus, we avoided the potential biases due to masking effects or piggyback effects that are likely to arise when factors are tested without adjustment.
We found a substantial heterogeneity in the ADRs between colonoscopists that could partially be explained by covariates. We showed that there was no correlation between the ADR and either case volume or colonoscopy outcome quality, which was corroborated with an even larger database from the German national registry. Although case volume plays a role in the quality of surgical procedures, case volume did not play a major role in determining SC quality in our study. The present study was the first to examine the influence of case volume on the effectiveness of diagnostic endoscopy. Investigations of case volume in the area of gastrointestinal endoscopy have only been analysed and shown for endoscopic retrograde cholangiopancreatography (with respect to complications). For diagnostic tests, outcome quality parameters, such as the detection of findings (the ADR in the present study), are probably more important parameters than complications, especially because complications are not that common in SCs. The present results have to be interpreted within the German screening programme, which sets a cut-off of 200 colonoscopies as the minimal annual number for accreditation. It could be that even lower annual numbers may show some correlation with the ADR. However, because recent European guidelines set a higher minimum level of required annual colonoscopies (ie, 300), we can conclude that 200 annual colonoscopies are sufficient to guarantee a quality that is independent of case volume.
The present study showed that certain colonoscopist- and endoscope-related factors contributed to the variation in the adenoma detection rates. Although these factors explained a substantial proportion (approximately 40%) of the variation, they did not explain all of the differences between the colonoscopists. The remaining heterogeneity is likely due to differences in the colonoscopists' skill levels that could not be directly measured in the present study.
Only a small number of factors that may influence the ADR have been analysed and found to be relevant, which may be due to the limited case numbers in previous studies. Interestingly, instrument withdrawal is probably the only influence shown in some studies to correlate with the ADR. In the present observational study, we did not subtract biopsy or polypectomy time from the overall examination times, which was similar to previous studies. Thus, we only used withdrawal times from the cases without polyps for our correlation, which may be a methodological limitation. In contrast to previous studies, we could not find any correlation between the withdrawal time and the ADR. This may be due to the self-selection of the physicians who participated in the study as none of them had withdrawal times below 6 min or detected less than 0.6 adenomas per patient. Furthermore, the effect of increasing withdrawal time on the ADR appears to be controversial. The US group that showed the most impressive correlation between withdrawal time and the ADR also studied the influence of a quality assurance programme. After implementing their protocol of careful inspection during a minimum of 8 min for withdrawal, they observed significantly greater rates of overall and advanced neoplasia detection during screening colonoscopies, but this might have also been due to greater colonoscopist attentiveness. Interestingly, a much larger study that systematically implemented a 7 min withdrawal protocol with an increase in adherence from 65% to 100% could not show any increase in the ADR. Therefore, if the true effect of withdrawal time is analysed further, different methodology (eg, measuring the times of all colonoscopies with a stopwatch, ie, halted during biopsy or polypectomy) and large patient numbers should be prerequisites.
To the best of our knowledge, no correlation between physicians' CME activities and their outcome qualities (ADR for colonoscopy) have currently been examined for colonoscopies or any other endoscopic procedures. A recent health technology review that analysed 136 articles and nine systematic reviews concluded that despite the limited overall quality of the literature, CME was effective, at least to some degree, in achieving and maintaining the objectives that were studied, including knowledge (22 of 28 studies), attitudes (22 of 26 studies), skills (12 of 15 studies), practice behaviour (61 of 105 studies) and clinical practice outcomes (14 of 33 studies). Only one paper dealing with endoscopy was mentioned; this paper focused on the training that is needed for novices to perform endoscopic procedures. The correlation of CME activities with ADR confirms previous evidence reported in a review that showed that almost two-thirds of the interventions in medical education led to an improvement in at least one major outcome measure in the various areas analysed. The present study was the first to show that interventions in medical education also appear to lead to improvements in screening colonoscopies. We can only speculate which part of the CME activities may have been responsible because the CME account did not specify which type of meetings were attended. However, larger scientific meetings and meetings with hands-on activities obtain higher CME points in the German system. Overall, a better understanding of polyp morphology and examination techniques, both of which are taught during a variety of meetings, may be correlated with better colonoscopy performance.
We believe that the correlation between the generation of the instrument and the ADR deserves some comments. Most studies that have analysed new imaging features, such as narrow band imaging, only compared the new feature within the same generation instrument using the same high quality scopes; these studies did not show any differences in adenoma detection rate. A recent meta-analysis that compared high-definition instruments with standard instruments from one generation earlier only found marginal differences in the adenoma detection rates. Among the five studies that were included in the meta-analysis, only two were randomised, and they did not show differences between the two subsequent generations of instruments. A small randomised study that compared two subsequent generations of instruments, however, found a large increase in the adenoma detection rate with newer scopes. In addition, a large comparative study that observed the same examiners using different generation scopes over two different time periods found a 15–20% increase in the adenoma detection rate by uniform use of the newest scopes as compared to older equipment from different generations. Thus, changes in several colonoscope features—for example, to be found when instruments are compared from the latest generations and those from two generations before—appear necessary before an effect on the adenoma detection rate can be observed in a larger study as with ours.
The present study had several limitations, such as the moderate number of participating colonoscopists (n=21) and their self-selection (ie, only colonoscopists with substantial experience agreed to participate in the study). In addition, we were not able to determine the generation of the instrument that was used on each patient; thus, we could not analyse the instrument effect in the practices that used instruments from multiple generations (that is, mixed generation instruments (n=8/21)). Nevertheless, we believe that the large number of examinations in the present study may counterbalance these limitations.
In conclusion, case volume cannot be taken as a quality parameter per se for screening colonoscopies above an annual colonoscopy number of 200. In countries with a quality programme that defines the minimal case load, case volume does not appear to be a parameter that patients have to worry about with respect to SC quality, and case volume is not suitable for benchmark comparisons. Both individual colonoscopist factors and instrument quality play a greater role than case volume in SC quality. Further studies are needed to show which measures are helpful in improving the quality of screening colonoscopies.