Cost-effectiveness analysis of immunochemical occult blood screening for colorectal cancer among three fecal sampling methods Yamamoto M, Nakama H

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1 Cost-effectiveness analysis of immunochemical occult blood screening for colorectal cancer among three fecal sampling methods Yamamoto M, Nakama H Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology Immunochemical occult blood screening for colorectal cancer using three different fecal sampling methods followed by a diagnostic examination (colonoscopy) for positive test results. Each participant provided fecal samples on three consecutive days. The first screening method was one-day testing using the sample from the first day only, the second method was two-day screening using the samples from the first and second days and the third method used the results from all three samples. Type of intervention Screening. Economic study type Cost-effectiveness analysis. Study population The study population consisted of adults aged 40 years and over without symptoms of colorectal cancer. Setting This study was set in Nagano prefecture, Japan. It was not clear whether the screening was carried out in primary or secondary care but the authors stated that the test can be used in an office or small hospital laboratory. Dates to which data relate The screening was conducted in No dates were given for the resource use or cost data. Source of effectiveness data The effectiveness data came from a single study. Link between effectiveness and cost data The resource use data were taken from the same patient sample as the effectiveness data. It was not stated whether data were collected retrospectively or prospectively. Study sample No sample size or power calculations were reported. The authors stated that a colorectal screening programme was conducted in five municipalities in Japan. There appears to have been universal screening of persons over 40 years of age since no other population characteristics were reported. It was not clear how the 9,638 participants were recruited. This study sample would be appropriate to study the cost-effectiveness of the screening methods in a general Page: 1 / 5

2 population. Study design This was a non-randomised multicentre study carried out in five municipalities. It was not stated whether the screening was carried out in primary or secondary care or in how many centres. Of the 597 subjects with positive fecal occult blood tests (FOBT), 504 had the colonoscopy representing an 84.4% compliance rate. Analysis of effectiveness The effectiveness numbers were adjusted under the assumption of 100% compliance with colonoscopy. The health outcome was cancer cases detected. The comparison was of different methods of screening on the same group of subjects, thus there was no possibility of confounding bias. Effectiveness results The one-day method revealed 372 positive results, the two-day method revealed 501 positive results and the three-day method revealed 597 positive results. The sensitivities and specificities were calculated to be 58% and 96% for the oneday method, 89% and 95% for the two-day method and 100% and 94% for the three-day method. The sensitivity of the one-day method was significantly different from the two- and three-day methods, (p<0.05). The specificities of the three methods were also significantly different, (p<0.001). Clinical conclusions The three-day method was assumed to be perfectly sensitive and the one-day method was significantly less sensitive. The three-day method was significantly less specific than the two-day method which in turn was less specific than the one-day method. Methods used to derive estimates of effectiveness The authors assumed that all cancer cases were detected by the three-day method (i.e. 100% sensitivity). They suggested that this study provided some information about the accuracy of the test but it was not clear how this related to the assumption of 100% sensitivity. They also assumed that all patients with positive FOBT undergo a colonoscopy rather than the 84% who actually complied. They stated that there was no significant difference in results between those based on hypothetical compliance and those based on actual compliance. Measure of benefits used in the economic analysis Cancer cases detected were the measure of health benefit. Direct costs The following health service costs were included: the costs of the FOBT slides and colonoscopies. The authors chose to exclude treatment costs to clarify the issue of optimal sampling frequency. Resource use and unit cost were reported separately. For the FOBT, the manufacturer's price per slide was used as the unit cost. The source of the colonoscopy cost was not stated. Average costs were used and these were not dated. Discounting was not relevant. Statistical analysis of costs The resource use and unit cost data were treated deterministically, with no allowance for uncertainty. Indirect Costs Page: 2 / 5

3 The authors also excluded "non-medical" costs to clarify the issue of sampling frequency. Currency The unit cost and price are reported in dollars (presumably US dollars) and in Japanese Yen. No conversion rates were reported. Sensitivity analysis No sensitivity analysis was carried out. Estimated benefits used in the economic analysis The one-day method detected 13 cancer cases, the two-day method detected 20.1 cases and the three-day method detected 22.5 cases. These figures were adjusted assuming 100% compliance with colonoscopy for positive results. The unadjusted numbers of cases were 11, 17 and 19 respectively. Cost results The total costs of the screening and diagnostic tests were $77, for the one-day method, $120, for the twoday method and $160, for the three-day method. Synthesis of costs and benefits Benefits and costs were combined in calculating the cost per case detected. The average costs per case detected were $5, for one-day testing, $6, for two-day testing and $7, for three-day testing. An incremental analysis was not performed. Authors' conclusions The authors suggested a two-day collection method based on the fact that it cost only slightly more per case detected than the one-day method but had greater diagnostic accuracy. CRD COMMENTARY - Selection of comparators In using average costs, the authors have implicitly compared the cost-effectiveness of each collection method with no screening. Comparing one-day screening with no screening was relevant if no screening was current practice (as in the NHS). But conditional on deciding to screen, the decision of how many samples to collect is an inherently incremental one. Thus it is more reasonable to compare two-day screening with one-day screening and three-day screening with twoday screening. It is not sensible to consider only no screening and three-day screening and ignore the intermediate options. Validity of estimate of measure of effectiveness The study design appears to have been appropriate for the study question. The study population appears to have been representative of those who would attend a universal screening programme for people aged 40 years or older. Since the three testing methods were performed on the same group of subjects, there was no need to randomise and no possibility of bias due to confounding. Validity of estimate of measure of benefit The authors used an intermediate outcome (cases detected). It would be helpful to know the health (e.g., QALY) impact of this since the methods have different sensitivities. Studies in the UK and Denmark have shown screening to have an impact on mortality from colorectal cancer. Page: 3 / 5

4 Validity of estimate of costs The authors chose to exclude the costs of treating any cancers detected. However, the choice of sampling frequency may affect subsequent treatment costs. If a screening method has a low sensitivity it may fail to detect asymptomatic cases which may then be more costly to treat when they eventually present. Also, this study used average test costs. The marginal costs of additional tests (i.e. of more frequent sampling) may decline because the capital equipment is already in place or because the testers learn by doing. Equally, if the testing facilities are already operating at capacity, marginal costs may be increasing. Other issues The analysis, though transparent, has methodological shortcomings. The authors seemed to conclude that two-day screening should be adopted because it is more accurate and only slightly more expensive than one-day screening. Thus, their judgement is of an incremental nature but is made arbitrarily. Why is it worth incurring the extra cost of the twoday method but not the three-day one? If current practice is no screening, the decision should be to choose the most effective method that falls within the boundary of acceptable cost-effectiveness. If the option were to move from oneto two-day screening, an incremental analysis should be performed and the decision based on the maximum willingness to pay for a cancer case detected. It is difficult to know what this value is. If the authors had included the costs of cancer treatment and final outcomes, these could be compared with a cost per life year gained or a cost per QALY. The assumptions that the three-day method is 100% sensitive and that colonoscopy is a perfect diagnostic test could have been subjected to sensitivity analysis or, if final costs and outcomes had been calculated, threshold analysis to see how far these assumptions can be relaxed before the screening programme is no longer cost-effective. The authors adjusted the effectiveness figures based on the assumption of 100% compliance with colonoscopy but state that actual compliance was more relevant than hypothetical compliance. While they claimed that there is no significant difference between these two scenarios, this appears to have been based on the assumption that those who comply are the same as those who do not: it may have been better had the figures not been adjusted. Implications of the study The authors suggested that two-day screening may be a cost-effective policy but did not take into account the impact of differently sensitive tests on eventual treatment costs. Source of funding Supported in part by Grants-in-Aid for Scientific Research (No ) from the Ministry of Education, Science and Culture of Japan and Cancer Research (No 8-2) from the Ministry of Health and Welfare of Japan. Bibliographic details Yamamoto M, Nakama H. Cost-effectiveness analysis of immunochemical occult blood screening for colorectal cancer among three fecal sampling methods. Hepato-Gastroenterology 2000; 47(32): PubMedID Indexing Status Subject indexing assigned by NLM MeSH Adult; Aged; Colorectal Neoplasms /diagnosis /economics; Cost-Benefit Analysis; Female; Humans; Japan; Male; Mass Screening /economics; Middle Aged; Occult Blood; Predictive Value of Tests AccessionNumber Page: 4 / 5

5 Powered by TCPDF ( Date bibliographic record published 31/10/2001 Date abstract record published 31/10/2001 Page: 5 / 5