Affiliations of authors: J. D. Lurie, Veterans Affairs Medical Center, White River Junction, VT; H. G. Welch, Veterans Affairs Medical Center, White River Junction, and Center for the Evaluative Clinical Sciences, Dartmouth Medical School, Hanover, NH.
Correspondence to present address: Jon D. Lurie, M.D., M.S., SPORT/The Spine Center, Dartmouth Hitchcock Medical Center, One Medical Center Dr., Lebanon, NH 03756-0001 (e-mail: jon.d.lurie{at}dartmouth.edu).
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ABSTRACT |
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INTRODUCTION |
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In the clinical trials, almost all positive FOBTs were followed-up with a complete colorectal evaluation (2,3). Typically, a single screening FOBT consists of three separate cards; the patient applies a fecal sample onto one card after each of three bowel movements and then returns the cards for processing by the laboratory. A recent clinical guideline by the American College of Physicians (7) states that any positivity on one or more cards should be followed-up with a complete colonoscopy or a flexible sigmoidoscopy with an air-contrast barium enema. Unfortunately, there is evidence that the follow-up of FOBT in the community is quite variable (3,8,9). This variation in follow-up may significantly increase the cost and decrease the effectiveness of screening and may lead some physicians to question the appropriateness of population screening (10).
In this study, we examined different diagnostic testing procedures following FOBT in elderly Medicare beneficiaries. Accurate description of current practice patterns may improve our understanding of how the efficacy of FOBT seen in clinical trials will translate into effectiveness when FOBT is used in an uncontrolled clinical environment. We attempt to shed light on the following two questions: 1) Are there additional costs that will likely accompany population screening? 2) Might the benefit of screening FOBT be lower in clinical practice than what is seen in controlled trials?
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METHODS |
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As part of work on the Dartmouth Atlas of Health Care (11), we used
data from Medicare's National Claims History System to study beneficiaries who received
FOBT. These files contain all physician claims for a 5% sample of Medicare Part B
beneficiaries. We excluded the few beneficiaries who were younger than age 65 years and the
small number enrolled in risk-contract managed care plans. Available information includes
Current Procedure Terminology (CPT) codes (12); International
Classification of Diseases, 9th revision (ICD-9), diagnostic codes (13); and the date of service. A detailed list of all CPT and ICD-9 codes used in these
analyses appears in Appendix Table 1.
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Cohort Selection
Approximately 55 000 beneficiaries had a claim for FOBT during the first 4 months of 1995. Because FOBT is relatively inexpensive, it may be performed more often than it is billed for. As a result, the 55 000 beneficiaries whom we identified may only be a subset of the Medicare population who received FOBT.
Medicare only recently approved payment for screening FOBT; therefore, there was no direct way to separate screening FOBTs from those obtained as part of a specific diagnostic work-up. However, we defined a cohort whom we believe represents a screening population, generally defined as a population that lacks any clinical evidence of the target condition. We excluded beneficiaries with claims-based evidence of conditions for which FOBT might be used diagnostically. Specific exclusion criteria included ICD-9 codes for any of the following: digestive system disease; general symptoms, such as anorexia, weight loss, or abdominal pain; anemia; or any neoplasm. Additional exclusion criteria included CPT codes for diagnostic tests, such as iron studies, bone marrow examination, liver function tests, or abdominal radiographs. Beneficiaries were excluded if any of these codes appeared in the 1995 claims data prior to or on the same day as the initial FOBT. The final study cohort included 24 246 people.
Definition of a Positive Screen
Although we do not know which FOBTs were positive, we used as a proxy measure those FOBTs that were followed by relevant diagnostic testing. Those beneficiaries who had a positive FOBT that was not acted upon would be missed by this definition. Those who had relevant testing for unrelated reasons would be falsely included.
Relevant Downstream Events
We followed each beneficiary in the cohort for 8 months after their initial FOBT and assessed the following three major categories of subsequent diagnostic testing: 1) complete colonic evaluationcolonoscopy or flexible sigmoidoscopy with air-contrast barium enema; 2) partial colonic evaluationflexible sigmoidoscopy alone, flexible sigmoidoscopy with single column barium enema, or a barium enema only; and 3) other gastrointestinal (GI) testingcomputed tomography or magnetic resonance imaging of the abdomen, upper GI series, serum carcinoembryonic antigen levels, or esophagogastroduodenoscopy.
One possible diagnostic follow-up for a positive FOBT is to repeat the FOBT (6). However, there are other reasons to repeat a FOBT, such as the specimen was inadequate, only one of the three cards was completed, or the specimen was placed on the wrong side of the card. As a result, we do not believe that repeat FOBT is a reliable indicator of an initial positive FOBT in the Medicare claims data and did not include it as part of our relevant downstream events.
Statistical Methods
We calculated 95% confidence intervals (CIs) by using the exact binomial CI function for proportions in StataTM Software (Stata Statistical Software, release 5.0, 1997; published by Stata Corp., College Station, TX).
To help confirm the validity of our cohort as a screening cohort, we estimated the positive predictive value of FOBT in the subset of patients receiving a subsequent complete colonic evaluation. We used this subgroup because these patients are the only ones in whom the presence of cancer or polyps (the numerator) can be reliably determined. Those people who did not receive a complete evaluation may have had colorectal cancer or polyps that remained undiagnosed during the study period.
We defined the positive predictive value as the proportion of beneficiaries with an FOBT followed by a complete colonic evaluation who had either colorectal cancer or polyps. To calculate the number of patients with disease (the numerator of the positive predictive value), we developed claims-based definitions for new cases of colorectal cancer and colon polyps. Colorectal cancer was defined as an ICD-9 code for any malignant neoplasm of the GI tract, including carcinoma in situ, which was accompanied by a CPT code for treatment: colonic surgery, endoscopic excision or fulguration, radiation therapy, or chemotherapy. The presence of polyps was defined by a CPT code indicating endoscopy with polypectomy. The denominator of the positive predictive value was all beneficiaries with a complete colonic evaluation (i.e., colonoscopy or flexible sigmoidoscopy plus an air-contrast barium enema) following their initial FOBT.
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RESULTS |
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Table 1 shows our primary findings: the numbers of people
undergoing various diagnostic tests per 1000 following FOBT. All results are rounded to the
nearest whole number per 1000. The proportion of all subsequent testing that occurred in each
category of follow-up testing is reported to the nearest whole percent; raw counts are available in
Appendix Table 2
. Approximately 32 (95% CI = 30-34 per
1000) people underwent the recommended evaluation for every 1000 receiving an initial FOBT;
however, this group represents only 34% of those undergoing subsequent diagnostic
testing. Almost as many people received a partial colonic evaluation (31 per 1000; 95% CI
= 29-34 per 1000) or one of the "other GI" tests without evaluation of the
colonic lumen (29 per 1000; 95% CI = 27-32 per 1000).
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In Fig. 1, we compare the results at 2 and 8 months following the
initial FOBT to determine whether the pattern of testing was sensitive to the length of follow-up.
Approximately half of all subsequent testing occurred within 2 months of the initial FOBT. The
pattern of testing at 2 months was similar to that at 8 months. Among beneficiaries receiving
subsequent testing within 2 months, 30% (95% CI =
27%32%) received the recommended evaluation compared with
34% (95% CI = 33%36%) at 8 months, 40%
(95% CI = 37%43%) received only a partial colonic
evaluation compared with 34% (95% CI = 32%36%)
at 8 months, and 30% (95% CI = 27%33%) received
other GI testing without an evaluation of the colonic lumen compared with 32%
(95% CI = 30%34%) at 8 months. Overall, the pattern of
testing was not very sensitive to the length of follow-up.
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DISCUSSION |
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We found an estimated positivity rate of 9.3%. It is quite possible that the real positivity rate in our cohort was higher but that some people received no follow-up testing at all. To the degree that this undercounting of a positive screen occurred, the proportion of people with a positive FOBT who received the recommended evaluation would be even lower than the 34% that we observed. Alternatively, the actual positivity rate may have been lower than 9.3%, and we may have overcounted by including unrelated follow-up testing. However, 9.3% is about what we would predict for a positivity rate in this cohort. The expected positivity rate is 2%4% with nonrehydrated slides and 8%16% with rehydrated slides (6). The positivity rate in our cohort should be at the high end of this range because the rate of FOBT positivity increases with age (3,14,15) and our entire cohort was 65 years old or older, with 40% older than age 75 years. However, even if we drastically overcounted and the actual positivity rate were only about 4%, there still would have been only three quarters of the beneficiaries who received the recommended follow-up.
Our findings of a low rate of recommended follow-up are consistent with previous data on
the work-up of positive FOBT in the community. Table 3 summarizes
some literature and puts our results in context. In randomized trials, the proportion of people with
a positive FOBT who received the recommended follow-up was as high as 90% (2). In the community setting, however, the proportion with the
recommended follow-up has been as low as 21% (8).
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A second limitation to our analysis is that we do not know the results of the FOBT or whether the subsequent testing was directly related to those results. Some of the subsequent testing could represent background testing unrelated to the FOBT or related to new conditions that emerged after the initial FOBT. Our exclusion criteria should have eliminated those beneficiaries with other clinical reasons for receiving the subsequent diagnostic tests that we studied. Of course, our exclusion criteria may have missed some patients with gastrointestinal problems. However, we are confident that the subsequent testing was related to the initial FOBT for two reasons. First, our finding that 9.3% of beneficiaries underwent subsequent diagnostic testing is consistent with the expected positivity rate and supports the hypothesis that we measured true follow-up testing. Second, the time course of subsequent testing, with half of all subsequent tests occurring in the first 2 months after the initial FOBT, strongly suggests a link between the subsequent testing and the initial FOBT. It is unlikely that new conditions arose after the initial FOBT to prompt testing in this short time frame.
Despite our efforts to confirm the validity of our findings, the reader might take the "other" diagnostic testing (computed tomography, magnetic resonance imaging, or carcinoembryonic antigen) as prima facie evidence that these tests were not done as part of screening for colorectal cancer. However, it is worth considering that this other testing may in fact represent real world practice. FOBT is relatively cheap, easy, and noninvasive; therefore, it may be ordered without much thought to follow-up. In fact, Cooper et al. (16) found that almost a third of primary care physicians surveyed would recommend FOBT even for a 75-year-old patient with unresectable non-small-cell lung cancer. However, when faced with a positive test and the prospect of an invasive follow-up test like colonoscopy, the physician or patient might reconsider. In the same study by Cooper et al. (16), physicians were often reluctant to recommend sigmoidoscopy even when it would have been appropriate. Thus, if FOBT were performed on some Medicare beneficiaries for whom physicians were reluctant to pursue endoscopy, these other tests might have been obtained as less invasive substitutes to follow-up on positive screens. This hypothesis is supported by the finding that these other GI tests were performed slightly more often on the older beneficiaries than on the younger ones. The low proportion of patients receiving the recommended evaluation may then represent a combination of incomplete follow-up in some case patients and a reconsideration of the initial screening decision in others.
Implications
We found a substantial amount of testing other than colon evaluations that occurred following FOBT. Some people might argue that this other testing is not extraneous but rather is indicated. In particular, Hsia et al. (17) showed that important upper GI tract lesions were common in patients with a positive FOBT. Similarly, a recent study (18) identified upper tract lesions as the cause of positive FOBT more often than colon lesions. Nearly 60% of these upper GI tract lesions resulted in a change in the patient's treatment. Thus, while upper GI tract evaluation is certainly ineffective for detecting colon cancer, it is not surprising that many physicians might pursue such testing after a positive FOBT. However, these additional tests represent substantial additional costs to screening that are largely ignored in formal cost-effectiveness models (19). Furthermore, including upper GI tract evaluation in the diagnostic follow-up of positive screening FOBT amounts to screening for upper GI tract lesions. Although these tests may detect important lesions, there is no evidence that screening for these lesions is beneficial. There is an important need to better define which follow-up diagnostic procedures are truly useful following screening FOBT.
Fueled by the knowledge of benefit from FOBT screening in clinical trials, there is almost unanimous endorsement of colorectal cancer screening with FOBT. However, screening FOBT is a complex task, and myriad clinical details will determine the effectiveness of population screening. The screening FOBT offers little benefit without proper follow-up testing and treatment. Thus, the effectiveness of screening will be reduced if only a small proportion of people receives the recommended follow-up evaluation. Our study suggests that, with current patterns of practice, population screening may be less effective than estimated from controlled trials.
We cannot determine from this study why only about a third of Medicare beneficiaries received the recommended follow-up testing. It may be that physicians were hesitant to recommend invasive testing in some patients and sought less invasive alternative follow-up tests. It may be that patients were hesitant to follow the physicians' recommendation for a complete colonic evaluation. It is important to note that, while our data were from 1995, the American College of Physician's guideline for colorectal cancer screening (7) was not published until 1997. Current physician practice may adhere more closely to the recommended complete colonic evaluation as consensus on the proper approach to colorectal cancer screening evolves. Further evaluation of current practice patterns following screening FOBT should help answer this question. Future work should focus on evaluating the usefulness of different follow-up tests after a positive FOBT, why physicians choose different follow-up tests after their patient has a positive FOBT, and patients' understanding of the downstream consequences of FOBT when they decide whether or not to be screened.
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NOTES |
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REFERENCES |
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Manuscript received March 30, 1999; revised July 20, 1999; accepted August 6, 1999.
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