Adverse Events After Outpatient Colonoscopy in the Medicare Population

Context The complication rates of colonoscopy are well established in middle-age patients but are not known for elderly persons. Contribution The authors measured 30-day rates of cardiac and gastrointestinal events in a random sample of 53220 Medicare beneficiaries who had outpatient colonoscopy and in a matched set of beneficiaries who did not. Rates were higher in colonoscopy patients, with advancing age and preexisting comorbid conditions (especially diabetes, heart failure, atrial fibrillation, stroke, and chronic obstructive pulmonary disease), and after polypectomy. Caution The study used diagnostic billing codes rather than medical record review. Implication Advancing age and an increasing number of comorbid conditions are reasons to be cautious about recommending colonoscopy. The Editors Since 1998, Medicare has covered colorectal cancer screening of average-risk beneficiaries age 50 years or older with fecal occult blood testing, sigmoidoscopy, and double-contrast barium enema. In July 2001, Medicare expanded this coverage to include screening colonoscopy. Use of colorectal cancer screening by Medicare beneficiaries has increased subsequent to the coverage (1). However, the increased use is largely attributable to colonoscopy (2). Primary care physicians play an important role in colorectal cancer screening. Physician recommendation is 1 of the strongest predictors of whether patients are screened (35). Guidelines suggest that providers and patients should discuss the advantages and disadvantages of the different screening tests (6). However, studies show that primary care physicians' discussions with patients about colorectal cancer screening lack key information, especially an explanation of procedure risks (7, 8). Of the 4 types of colorectal cancer screening tests recommended by major expert groups (911), colonoscopy is the most invasive and has the greatest risk for complications. Yet, studies documenting adverse events after colonoscopy are limited because they have included persons of all ages and, in some studies, adverse events have not been the main focus of the analysis (1225). Despite the increasing use of colonoscopy in elderly persons, no population-based studies have examined the risks of colonoscopy in elderly persons. Recent guidelines note that complications of colonoscopy by age cannot be estimated because of the limitations of currently published studies (26). We address this gap in the literature by determining risks for adverse events after outpatient colonoscopy in elderly persons. We also assess whether particular patient subgroups are at increased risk for adverse events. Information about the risks of colonoscopy can assist primary care physicians with recommendations about the most appropriate method of colorectal cancer screening for older patients. Methods Overview We used Medicare data to identify a cohort of beneficiaries who underwent colonoscopy between 1 July 2001 and 31 October 2005. Medicare claims are longitudinal, allowing us to determine adverse events resulting in emergency department or hospital use within 30 days after colonoscopy. Claims were also used to assess the presence of selected health conditions in the year before colonoscopy. In addition, we used the Medicare data to identify a comparison group of beneficiaries who had not undergone colonoscopy. The comparison group enabled us to estimate the baseline risk for adverse events in the elderly population. Data Sources Data for this analysis came from a random 5% sample of Medicare beneficiaries who resided in one of the Surveillance, Epidemiology, and End Results cancer registry areas (27), which represent about 25% of the U.S. population. For these beneficiaries, we reviewed their physician, outpatient, emergency department, and hospital claims. Diagnoses and procedures are reported on Medicare claims by using Healthcare Common Procedure Coding System (28, 29) and International Classification of Disease, Ninth Edition, Clinical Modification (ICD-9-CM), codes (30). The Appendix Table lists the codes used to identify all diagnoses and procedures in this analysis. Appendix Table. Identification Codes for All Diagnoses and Procedures Defining the Cohort and Colonoscopies We identified 118002 colonoscopies from Medicare physician bills. The analysis included colonoscopies performed in the outpatient setting. We excluded procedures that were performed in the inpatient setting (n= 20814), those coded by the physician as incomplete (n= 810), and those done in persons at high risk for perforation. The latter group included persons with a diagnosis of diverticulitis, Crohn disease or ulcerative colitis, or colorectal cancer (n= 3139). We limited the cohort to persons age 66 to 95 years at the time of their procedure (8430 persons younger than 66 years were excluded) in order to have 12 months of claims before the colonoscopy that could be reviewed for the presence of comorbid conditions. To ensure complete data for the analysis, we required all patients to have continuous enrollment in Medicare Parts A and B and fee-for-service coverage during the year before their colonoscopy and for 30 days after the procedure (7014 persons were excluded on this basis). The date of the procedure was determined from the physician claim. We also removed from the analysis 4421 patients who had more than 2 colonoscopies during our study period and 812 patients who had 2 colonoscopies less than 60 days apart. Finally, we excluded 12912 persons who had their procedure outside of a SEER area because we did not have complete data for these cases. We assigned each outpatient colonoscopy to 1 of 3 categories: screening, diagnostic, and procedures with polypectomy. We used procedure codes on the colonoscopy claim to classify the type of procedure. In addition, procedures with a pathology bill for examination of a colorectal polyp within 7 days of the procedure were classified as polypectomies. Per Medicare coding policy, colonoscopies that were initiated as screening or diagnostic procedures are coded as polypectomy if polyps were removed during the procedure. Therefore, our polypectomy group comprised persons who underwent colonoscopy for screening and diagnostic reasons. Each procedure needed to be accompanied by an ICD-9-CM diagnosis code that identified the reason for the procedure. We used these codes to determine why the colonoscopy was performed. We assessed adverse events after outpatient colonoscopy. We used a matched cohort design, identifying a comparable group of Medicare beneficiaries who had not undergone colonoscopy from 1 July 2001 to 31 October 2005. For ease of reference, we refer to persons undergoing colonoscopy as the colonoscopy group and their matched cohort as the matched group. We used the matched group to determine whether the risk for adverse events observed in the group undergoing colonoscopy was higher than that in the general Medicare population. All potential matches were randomly assigned a pseudo-date of procedure that corresponded to the procedure date for the case patients, as has been done in other analyses (31). Characteristics used in matching each person in the colonoscopy group with a person in the match group were birth year, procedure year, race, sex, state or county of residence, and comorbidity score. We excluded colonoscopies with no corresponding beneficiary in the match group (n= 473). Our final cohort consisted of 53220 colonoscopies. Adverse Events We identified all adverse events occurring within 30 days after outpatient colonoscopy that were severe enough to require an emergency department visit or hospitalization. For the matched group, we identified all adverse events within 30 days of the pseudo-date of procedure. The 30-day risk for adverse events requiring an emergency department visit or hospitalization was calculated per 1000 procedures. Adverse events were classified into 3 groups: serious gastrointestinal events (perforation, gastrointestinal bleeding, or the administration of blood transfusions), other gastrointestinal events (paralytic ileus, nausea, vomiting and dehydration, abdominal pain), and cardiovascular events (myocardial infarction or angina; arrhythmias; congestive heart failure [CHF]; cardiac or respiratory arrest; or syncope, hypotension, or shock). We did not include death as a complication because the number of deaths was too small to provide statistical power (53 of 53200 colonoscopies) and the cause of death cannot be determined from claims data. Measurements Variables included as covariates in the models were patient age group, race, sex, and state and county of residence, all of which are reported in the Medicare data. Information about whether a patient resided in an urban or rural location was based on a link to the Area Resource File (32). We used U.S. Census data associated with the ZIP code of the patient's residence to measure his or her socioeconomic status. These proxy variables included information at that ZIP code level about the median household income, percentage of persons with a college education, and percentage of households with foreign-born persons. Comorbid conditions were identified from diagnoses reported on physician and hospital claims in the year before the procedure date by using Romano and colleagues' modification of the Charlson comorbidity index (33, 34). Although a summary measure of comorbidity is useful to ensure comparability between the colonoscopy and matched groups, it does not provide information about the risk for adverse events for persons with specific health conditions. We therefore identified 5 comorbid conditions that are common in elderly persons: diabetes, stroke (cerebrovascular accidents and transient ischemic attacks), chronic obstructive pulmonary disease (COPD), atrial fibrillation, and CHF. We obtained our data primarily from Medicare claims. We had no missing information for patients' age, race, sex, or resid