Colorectal cancer (CRC) is the third most common cancer and third leading cause of cancer death in Kansas (1). In 2002, the US Preventive Services Task Force (USPSTF) strongly recommended that people aged 50 years or older be screened for CRC on the basis of evidence that screening is effective in reducing CRC mortality rates (2,3). As a result of this recommendation, CRC screening has been widely promoted by many groups, including the National Cancer Institute, the Centers for Disease Control and Prevention (CDC), and the American Cancer Society (ACS). Use of CRC tests among US adults has been increasing (4–6). From 2000 to 2010, the percentage of US adults aged 50 to 75 receiving any CRC screening test within recommended intervals increased from 38.6% to 59.1% (4,7). At the same time, CRC incidence has been declining and the proportion of cases diagnosed at a localized stage has been increasing, trends attributed to a combination of risk-factor reduction and increased screening rates (8). However, CRC screening rates still lag behind those for other effective cancer screening tests. In 2010, less than half of CRC cases were diagnosed at a localized stage in both Kansas (41%) and the United States (39%) (1,7,9). Although CRC screening is promoted as a key tool for improving CRC outcomes, few data are available on how often CRC cases are identified through screening or surveillance in asymptomatic patients versus diagnostic workup for symptoms, particularly at the population level. Documenting trends in CRC identification methods could provide additional insight into the contributions of screening to CRC prevention and morbidity reduction. In addition, analyses of patient and tumor characteristics by identification method could identify population subgroups not benefiting from CRC screening and tumor subgroups not amenable to identification by screening. We sought to explore the circumstances leading to the identification of CRC, to examine relationships between identification method and patient and tumor characteristics, and to develop a process for assessing CRC identification methods among Medicare-linked CRC cases from a population-based cancer registry.

A total of 1,589 CRC cases who met the study eligibility criteria were included in the analysis. Of these, 1,333 patients had a claim for any CRC test in the 60 days before diagnosis. The distribution of CRC test use included 1,257 with colonoscopy, 176 with FOBT/FIT, 140 with sigmoidoscopy, 40 with double-contrast barium enema and 2 with CT colonography. There were 267 patients who had claims for more than 1 type of CRC test in the 60 days before diagnosis. Nineteen percent (n = 294) of the patients were classified as having screening- or surveillance-identified CRC (Table 2). Patients with screening/surveillance-identified CRC were more likely to be diagnosed at a local stage (P < .001), aged 65 to 74 years (P < .001), and married (P = .003). Patients with a colonoscopy claim were more likely to be classified as having screening- or surveillance-identified CRC than patients with claims for another CRC test (23% vs 3%, P < .001).

In the bivariate analysis, younger age, male sex, and being married were significantly associated with increased odds of having screening/surveillance-identified CRC (Table 3). Low-income patients were significantly less likely to have screening/surveillance-identified CRC (P = .05). In the multiple logistic regression analysis, only being aged 65 to 74 years remained a significant predictor of having screening- or surveillance-identified CRC. Compared with this age group, patients aged 75 to 84 years had 41% lower odds of having screening- or surveillance-identified CRC; patients aged 85 years or older (P < .001) had 72% lower odds.

In this study we developed a process for assessing CRC identification methods among Medicare-linked CRC cases from a population-based cancer registry by expanding on a previously published algorithm for determining colonoscopy indication. To maximize the number of CRC cases eligible for identification method classification, we also considered use of other CRC tests and symptom history among those without colonoscopy claims. Using our method, 19% of the Medicare-linked CRC cases diagnosed in 2008–2010 in Kansas were identified through screening or surveillance, while 81% were diagnostic-identified. Our finding of 19% screening/surveillance-identified in a population-based CRC cohort is consistent with that reported in a CRC cohort served by a single major medical institution (20%) during 2004–2011 (14). Another study in a health care system and a community hospital during 2002–2004 found that 9% of CRC cases were screening-identified (15).

Certain factors could contribute to misclassification of identification method for CRC cases. First, it is possible that CRC test procedure codes and CRC-related symptom diagnosis codes for some patients were not documented in their Medicare claims history, either because of coding errors or because claims were sent to another payer (16–19). To minimize the impact of patients with non-Medicare primary payers before CRC diagnosis, we used the primary payer fields in the KCR database to identify patients with other sources of insurance and manually reviewed the completeness of their claims history. Of the patients included in the study, only 21 cases (1%) had a sole non-Medicare primary payer in the KCR database. Second, the 60-day window before diagnosis that we chose may not have captured all CRC-related tests. Sixteen percent of the patients (n = 256) in our study did not have a claim for a CRC test in the 60 days before diagnosis and as a result were classified as diagnostic-identified. This apparent lack of CRC testing could be legitimate because the patient was diagnosed through other means (eg, diagnostic imaging) or could be an artifact introduced by inaccurate diagnosis dates. We further examined the claims and KCR records for these 256 patients and found that 228 patients had a claim with a CRC-related symptom code within a year before diagnosis and an additional 15 patients had symptoms documented in the KCR database. Patients without CRC tests were more likely than their counterpart patients with CRC tests to have a CPT code documented for a diagnostic radiology procedure of the abdomen or pelvis (X-ray, CT, or MRI) in the 60 days before diagnosis. These insights increase our level of confidence in classifying these 256 patients as diagnostic-identified.

We found that CRC patients aged 65 to 74 years and who were male and married had increased odds of having screening/surveillance-identified CRC compared with their counterparts at the time of CRC diagnosis. However, younger age at diagnosis was the only factor associated with having screening/surveillance-identified CRC after adjusting for sex, marital status, comorbidity index, and income. Although low income had a marginal association with increased odds of having diagnostic-identified CRC, the significance level was diminished after adjusting for other risk factors.

The observed decrease in screening/surveillance-identified CRC with increasing age could be due to several factors. Changes in CRC screening recommendations and Medicare coverage for CRC screening have occurred since 1998 (2,20). The 2002 USPSTF recommendation applied to all adults aged 50 or older without regard to an age at which to stop screening, but in 2008 the USPSTF recommended routine cancer screening to begin at age 50 and continue only until age 75 (in people with adequate screening histories). It is reasonable to assume that these changes affected various age cohorts differently; older patients would receive less lifetime benefit from recent improvements in screening technology and availability. We did not have access to enough claims history to evaluate long-term adherence to CRC screening recommendations for the patients in our study but historically low CRC screening rates indicate that many of the patients in the older age groups had an adequate history of negative screenings before their CRC diagnosis. Independent of screening recommendations, physicians may be less likely to recommend CRC screening in older people because of significant comorbidities, limited life expectancy, or both (21–23).

Understanding CRC screening patterns is important for CRC prevention and control at a population-based level. Unfortunately, estimating population-level use of CRC screening and the extent to which it contributes to CRC identification remains challenging, because no single data set is readily available to address this question. Various data sources including Medicare and Medicaid claims files, medical records, and surveys have been used to address this question but each has its own limitations and unique issues. Still, no single source exists for reliable information about how frequently CRC is identified through screening versus diagnostic workup. To examine CRC identification methods, our study not only used Medicare claims files to identify CRC tests but also considered CRC-related symptoms documented in the Medicare claims files as well as data in the Kansas Cancer Registry.

As with any evaluation of clinical practice that relies on administrative claims data, a limitation of our study is the generalizability of our findings. The clinical experiences of the Medicare population and the way these experiences are reflected in their claims history may not be generalizable to other groups. However, despite this limitation, we believe that the combination of administrative claims data with population-based registry records can offer novel and important insights into screening patterns and identification methods among people diagnosed with CRC and that these techniques could also be extended to other screen-detectable cancers.