To our knowledge, this is the first study to investigate CRC screening prevalence and predictors in a large, national cohort of AI/AN. Our study determined that only 4.0% of asymptomatic, average-risk AI/AN receiving IHS medical care underwent recommended CRC screening between 1996 and 2004. Women and residents of the Alaska region were more likely to have been screened, but even among women in this region screening was only undertaken 10.8% of the time.
The CRC screening prevalence we detected is below previously published results for AI/AN [4
] and below those for the overall U.S. population [25
]. While there is marked variation in the reported prevalence of CRC screening among AI/AN, with estimates ranging from 26 to 44% [4
], all these estimates exceeded what we discovered. Methodological designs of past studies may in part explain their elevated reported screening compared to ours. CRC screening estimates from previous studies encompassing a similar timeframe as ours are largely based on telephone surveys and patient self-reported questionnaires which introduce recall and selection biases and examine a distinct group of AI/AN who had access to land-line telephones, spoke and understood English and were willing to participate [14
]. Furthermore, some of these studies focused on a small sample of AI/AN within one specific geographical region and did not examine IHS healthcare users [12
Our low CRC screening prevalence requires explanation. Attitudes and perceptions play an important role in people who decide to undergo screening. The lack of understanding CRC screening benefits [26
], concerns or embarrassment [29
], and implications from receiving a diagnosis of CRC [26
] all contribute to lower screening prevalence. Some of these issues have been reported in small studies of AI/AN [12
]. Also, refusal and lack of adherence to screening is higher in minority populations [30
]. However, this has yet to be directly studied in the AI/AN community and such issues may play a role in the low CRC screening prevalence we observed. Furthermore, IHS healthcare providers may not recommend CRC screening, may be unfamiliar with CRC screening guidelines, or they may be impeded by insufficient funding. Another potential barrier to CRC screening may be a limited capacity to provide endoscopic services for screening. Access to specialty care within IHS can be challenging due to limited resources and geographic location thereby limiting the number of trained physicians able to perform endoscopy for screening purposes.
CRC screening predictors may shed light on the cause of the low prevalence of screening we found. We confirmed that geographic region and sex were important predictors, both of which have been reported previously [12
]. One of the strongest predictors for screening pertained to geography. Regional differences in CRC screening are key in that they not only reflect the diversity of the AI/AN community, but exemplify potential differences in access to CRC screening, financial resources, and cultural beliefs about screening. Additionally, regional disparities draw attention to programs aimed at increasing screening within particular communities as well as individual screening preferences by local IHS leadership. Our finding that residing in Alaska was one of the strongest screening predictors reflects a concerted effort by the tribal leadership, IHS, and the Centers for Disease Control and Prevention to increase CRC screening in this community using endoscopy [33
]. A similar result was reflected in the Pacific Coast where there has been an increased effort to use FOBT for CRC screening [35
There was a trend toward increased screening with a greater number of co-morbid medical conditions compared to lower CRC screening in patients with multiple primary care visits. Such a finding appears contradictory to what is reported in the literature [36
]. One possible explanation is that patients in our study with multiple primary care visits may represent a distinct group with other social issues or complex medical problems that are not reflected in the number of co-morbid medical conditions. AI/AN have higher rates of substance abuse, tobacco usage, and obesity resulting in more complex medical and social problems compared with other groups [14
]; all conditions not easily captured in the number of co-morbid medical conditions. Also, healthcare providers may be less inclined to recommend CRC screening to patients with more primary care visits as this may represent a subset of patients who are less compliant with their medications, have a poorer understanding of their disease process, or have diseases that may preclude them from invasive CRC screening.
Another finding of our study was the high CRC incidence estimated among AI/AN IHS users. The age-adjusted CRC incidence rate of 227 cancers per 100,000 person-years is higher than previously reported [2
]. In comparison, using 2006 SEER data, age-adjusted CRC incidence for the U.S. population for individuals older than 50 years was 150 cancers per 100,000; for African-Americans it was 184 cancers; and for Caucasians it was 148 cancers [37
]. Our rate should be interpreted with caution. Our study only examined IHS patients and was limited to a specific age range. We relied on ICD-9 codes to document CRC rather than on a histological diagnosis as has been performed in previous analyses [2
]. Also, miscoding of CRC using ICD-9 codes may occur using RPMS data. To our knowledge, there are no studies available that directly assess the reliability of ICD-9 coding and the diagnosis of CRC in IHS patients using RPMS data. A separate study that examines ICD-9 coding in RPMS and CRC diagnosis with confirmation using IHS medical records would be helpful but has yet to be conducted. Finally, persons eligible for IHS services but less likely to seek them, such as those not experiencing symptoms, are less likely to be included in the analysis.
While our overall CRC incidence for AI/AN was high, more strikingly, significant geographical variation existed in CRC detected among IHS AI/AN. This variation was most notable among Alaskan Natives who had three times the CRC incidence rate of other regions. Our findings that geography was linked with higher rates of CRC have been illustrated in previous studies [2
]. One potential reason for this discrepancy in CRC incidence may relate to differential prevalence of CRC screening. CRC screening is a vital tool in the early detection of CRC and the removal of precancerous lesions (polyps) and has led to important reductions in CRC incidence and mortality [1
]. However, AN had nearly ten times the rate of screening compared with other regions indicating that other factors aside from screening may profoundly influence CRC incidence among this group. A number of alternate theories have been postulated to account for these differences in CRC incidence. One possible reason is that geography itself has shaped the risk for CRC in AN: Alaska is separated from the transcontinental U.S. by significant distances and this can affect CRC incidence in many arenas in comparison with other regions of the U.S. Lifestyle factors may contribute to the development of CRC. For example, tobacco usage [39
], higher alcohol consumption and binge drinking [39
], sedentary lifestyle [39
], and obesity [39
] increase one’s risk for CRC; all of which have been consistently shown to be significantly higher in AN compared with other AI in IHS regions [14
]. Also, geography encompasses cultural differences that may include diet and use of alternative medications which may impact CRC incidence. Again, AN have diets low in fruits and vegetables [14
] which may increase their risk for CRC compared to other AI [42
]. Lastly, varying CRC incidence among regions may also reflect a genetic component in the development of CRC among AI/AN. All these factors, either separately or acting in concert with one another, can play a role in the higher CRC incidence noted in AN.
Several limitations may influence the interpretation of our study. First, methodological considerations may have underestimated CRC screening prevalence. In particular, distinguishing between screening and diagnostic/surveillance examinations using RPMS data is challenging. We systematically excluded patients with symptoms/diseases that would have resulted in further endoscopic evaluation for non-CRC screening purposes thus resulting in a more representative patient population of average-risk individuals. Second, IHS provides healthcare to approximately 57% of U.S. AI/AN that are mostly a rural population thereby limiting the generalizability of our results. Third, a subset of IHS patients may have received CRC screening from another health care facility outside of IHS for which we could not account. This data are exceedingly difficult to capture and has not been extensively studied. To date, the only study to examine this issue was a small pilot study that examined the medical records of IHS patients identified as having undergone CRC screening in five IHS facilities. This data demonstrated that only a small fraction of patients underwent screening at a facility outside of IHS (0.6%) [43
]. The number of IHS users who may select to have CRC screening at outside facilities may be higher than this estimate but currently such information is unavailable. Thus, while patients do have the option to obtain CRC screening at facilities outside of IHS limited data suggest that this number is small and unlikely to affect our results. Currently, a survey of IHS sites is being conducted which is assessing CRC capacity and will provide a much better estimate of what is performed within IHS healthcare facilities versus referral. A fourth limitation is that data beyond 2004 may reflect a more accurate representation of CRC screening prevalence for AI/AN. However, our study period overlaps with other studies, few studies exist examining screening in AI/AN after 2004, and the available studies do so only from a regional perspective [12
]. Also, we used coding data to represent CRC screening and this raises issues of systematic and random coding errors occurring in our dataset. Only one small (618 patients), unpublished study has addressed this issue. In this study, the authors discovered a 25% misclassification rate between screening and diagnostic colonoscopy for IHS patients. Further examination of their data revealed a miscoding rate of only 7.6% and was based overwhelming on the use of one specific ICD-9 code that we did not utilize to capture screening methods for our study. Also, this study did not exclude patients who had previously documented symptoms that may have led to a diagnostic endoscopy, a method that we employed in our analysis [43
]. Lastly, a vast majority of IHS AI/AN individuals had multiple comorbid medical conditions which may introduce some ascertainment bias into our results. However, this finding is not surprising given that AI/AN are disproportionally affected by more chronic diseases such as diabetes, hypertension, heart disease, and several forms of cancer when compared with other racial groups [4
]. Moreover, as previously discussed, AI/AN have elevated rates of long-term tobacco usage and alcohol consumption compared with other groups thus predisposing them to the multiple medical consequences/diseases of such usage which is likely reflected in our data. Also, patients with chronic diseases are more likely to seek health care and thus be a part of the IHS medical system as compared with healthy, asymptomatic patients who are less likely to seek care. Despite these limitations, we believe our study adds an important perspective in portraying CRC screening prevalence among average-risk AI/AN.
In conclusion, CRC screening among asymptomatic, average-risk AI/AN who used IHS for medical care was extraordinarily low from 1996 to 2004. Unexplained discrepancies exist in CRC screening prevalence based on sex, geographic location, and health-care utilization. The low prevalence of recommended screening for AI/AN served by IHS is disturbing and highlights potential areas where efforts for awareness and access to CRC screening should be directed.