The risk of serious complications within 30 days after screening and surveillance colonoscopy was low in our study, with an incidence of perforations of 0.19/1000 exams and gastrointestinal bleeding requiring hospitalization in 1.59/1000 exams. The overall incidence of serious, directly related complications was 2.01/1000 exams, and the incidence of all directly and potentially related events was 3.18/1000 exams (). Immediate procedure-related complications were uncommon (), and aggressive intervention such as administration of reversal medications was infrequent.
Patients who underwent snare polypectomy with cautery had a significantly increased risk of serious complications. Risk increased even further if more than one polypectomy with cautery was performed. We also identified clinical characteristics associated with higher risk. Most notably, the incidence of complications was higher in patients who used warfarin prior to colonoscopy, but was not significantly associated with use of aspirin or non-steroidal anti-inflammatory agents. Data on whether warfarin was stopped before the procedure and the length of time it was withheld were missing in 40% of patients, so we could not analyze how these practices may affect complication risks. Further studies of these issues may help understand the association between colonoscopy complications and the use of this medication. In addition, warfarin use may be a surrogate marker for higher comorbidity, which was not captured well by the data about ASA classification that was available from the colonoscopy reports. Although there was a suggestion that complication rates increased with age, age was not statistically significant in the logistic model. We did not find a significant association between provider characteristics, such as practice setting, trainee participation, or endoscopists’ annual colonoscopy volume, and the risk of complications. However, CORI endoscopists during the study period were fellowship-trained gastroenterologists, and we could not examine the effects of endoscopist specialty. We did not have data about years in practice or board certification to determine if these were related to complication rates.
The risk of perforation in our study is slightly lower than in other published studies 8-10, 18, 19
. Levin, et al., found an incidence of perforation of 0.9/1000 colonoscopies, and an incidence of gastrointestinal bleeding of 3.2/1000 colonoscopies 19
. In this study, the risk of perforation or bleeding in colonoscopies with biopsy or polypectomy was similar to ours. Our lower overall risk of complications may be due to a lower proportion of colonoscopies with biopsy or polypectomy. Rabeneck, et al., also identified polypectomy as a risk factor for complications 18
. In contrast to our study, having a colonoscopy performed by a low-volume endoscopist was a predictor of complications. We did not find a statistically significant association between colonoscopy volume and complication risk, but the small number of colonoscopies performed by low-volume providers in our study limited our ability to address this question. Finally, Warren, et al., using Medicare claims data, found a perforation rate of 0.7/1000 exams, and also found an association of complications with use of biopsy or polypectomy, and with increasing age and comorbidity 17
. Their perforation rates may be slightly higher than ours because they included a larger proportion of older patients, and included exams done for both diagnostic and screening indications.
We used data from the American Heart Association to calculate expected rates of myocardial infarction and stroke in a population with comparable age, sex, and racial distribution 22
. The expected annual adjusted rate of myocardial infarction is 5.0 per 1000, or 0.49 per 1000 over 30 days, comparable to the rates we found here. The expected annual adjusted rate of stroke is 4.9 per 1000, or 0.48 per 1000 over 30 days, again comparable to our results. These findings are similar to those of Warren, et al 17
This study has several strengths. First, unlike most prior studies, we focused primarily on screening and surveillance colonoscopy. This is a large study with follow-up until 30 days post-colonoscopy. Data were collected prospectively in diverse practice settings, with a majority of patients enrolled from community-based practices where most colonoscopies are performed. Because we had access to the CORI data repository, we had detailed information about the colonoscopy itself, including procedure indications and type of biopsy or polypectomy performed. We collected data about pre-procedure use of aspirin, non-steroidal anti-inflammatory agents, warfarin, and clopidogrel to examine the influence of these medications on complication risk.
Our study has some limitations. First, our overall enrollment rate was 53%, potentially biasing our estimates of complication rates. However, the demographic and clinical characteristics of enrolled and non-enrolled patients were generally similar. It is difficult to know the potential magnitude and direction of bias introduced by our enrollment rate. Non-enrollment may be associated with better outcomes as unenrolled patients without adverse events may have declined to participate. Conversely, it is also possible that we could not contact patients with poor outcomes, so that non-enrollment was selectively biased towards patients who had experienced complications. To examine the possibility that subjects were not enrolled because they had experienced a serious colonoscopy complication, we queried the National Death Index to identify potential deaths in non-enrolled patients, and did not find any deaths that could be definitively linked to the colonoscopy. As mentioned above, we did identify one death in a non-enrolled subject when the subject’s family member was contacted at 30 days. Because we could not follow all enrolled subjects to 30 days, we may have under-estimated complication rates. However, the estimated incidence of complications was similar in all enrolled patients and in secondary analyses including only patients with complete follow-up. In the CORI software, there are not standardized definitions for immediate complications such as hypotension or bradycardia. However, endoscopists are asked about the occurrence of unplanned events or the need for unplanned interventions. By ascertaining events in this manner, the colonoscopy reports are likely to capture events that the endoscopist considers clinically significant. In order to ensure adequate ascertainment of these events, endoscopists are required to complete the data entry fields for immediate complications before a colonoscopy report can be finalized.
We did not have detailed information on specific comorbidities but rather used the ASA classification as a general measure of comorbidity. Thus, we could not determine which individual comorbid conditions were associated with complication rates. Finally, CORI endoscopists are generally fellowship-trained gastroenterologists who may differ in important ways from endoscopists who do not participate in CORI, such as having greater interest or expertise in endoscopy. Participating endoscopists may therefore experience different complication rates from endoscopists in general, potentially affecting the generalizability of our results. Nevertheless, our study examined procedures performed in diverse community practice settings as well as academic and VA settings.
In conclusion, colonoscopy is a key colorectal cancer screening modality, but may be associated with higher complication rates than other less invasive screening modalities. We found that complications from screening and surveillance colonoscopy are uncommon, with serious complications directly related to the colonoscopy occurring in approximately 2 of 1000 exams. The overall rate of hospitalizations within 30 days for directly and potentially related events was 3.18/1000 exams. We identified some characteristics associated with higher complication rates, including polypectomy with cautery and pre-procedure warfarin or clopidogrel use. These results may help inform patients, physicians, and policy makers in examining the different options for colorectal cancer screening.