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1 Department of Public Health and Epidemiology, Public Health Building, The University of Birmingham, Edgbaston, Birmingham B15 2TT, 2 Department of Surgery, Queen Elizabeth Hospital, Birmingham B15 2TH and 3 Department of Specialist Radiology, Level 2 Podium, University College Hospital, 235 Euston Road, London NW1 2BU, UK
Correspondence: Dr Tengbin Xiong, Department of Public Health and Epidemiology, University of Birmingham, Public Health Building, Birmingham B15 2PT, UK. E-mail: xiongt{at}adf.bham.ac.uk
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Abstract |
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Introduction |
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The prevalence of extracolonic findings found at CTC is high [10]; when CTC is used as a diagnostic method in symptomatic patients, 52% of patients have one or more incidental lesions [11]. While detection of potentially curable lesions such as an early renal cell carcinoma would benefit many patients, other lesions such as resorbing uterine fibroids are of no importance. CTC may not provide sufficient specificity to fully characterize lesions detected in other intra-abdominal organs, thus initiating further investigations and even surgical interventions for lesions that turn out to be benign. The costs to the patients and health services of these investigations and treatments must be offset against the potential benefits of detecting serious diseases earlier than would otherwise have been the case.
In a previous paper we recorded the ratio of potentially serious to totally benign incidental extracolonic findings from 225 consecutive CTC examinations involving patients with symptoms of bowel disease [11]. In the current study we quantify the direct resource and cost consequences of clinical follow-up of these extracolonic abnormalities.
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Methods |
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We excluded those few cases (n = 4) where the diagnosis of the extracolonic lesions preceded the colonography, since the costs of investigating these lesions were clearly not contingent on use of CTC. Likewise, we also excluded patients (n = 8) whose extracolonic findings were metastatic lesions from a primary colorectal tumour, since it is unlikely that any further investigation in such cases could have been avoided by a different primary diagnostic method; on the contrary, extracolonic findings may have saved costs in some of those cases – a point that we examine, from a sensitivity analysis perspective, in the discussion. This left 104 patients with one or more previously undiagnosed extracolonic lesion unrelated to bowel cancer. 24 of these 104 patients (23%) underwent further actions.
In the current study, we record and classify all the further actions that were taken in response to detection of extracolonic findings in these 24 patients. The cost data for further clinical actions among these patients were derived from NHS Reference Costs manual for 2004 [12]. Costs included those of further tests, outpatient attendances, inpatient and day case activities and other relevant accessed services. All inpatient elective and non-elective costs were based on HRGs (healthcare resource groups) to which we added the costs for inpatients stays that exceeded the norm for that particular procedure – so called "excess bed days". This methodology follows that laid down in the NHS Costing Manual [13].
The calculations were restricted to costs incurred by the NHS; indirect costs such as out-of-pocket expenses incurred by patients and lost productivity were not included. Costs for general practitioner (GP) consultations were also not included since they could not be captured in the scope of this study – again, we return to this issue in the discussion.
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Results |
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. The data are summarized in Table 2, where we classify the resource consumed according to the NHS reference cost categories; for example, elective surgery, outpatient appointments and radiology services. The total cost of all actions contingent on incidental lesions among the 24 included patients was £34 329. Averaged over the sample of 225, this amounts to £153 per patient. 11% of patients (24 out of 225) underwent at least one further action and the 95% confidence limit on this proportion ranges from 7% to 15%. Extrapolating the cost estimates across this range provides a cost interval of £97 to £208.
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Of all the patients with extracolonic findings who underwent further action, 75% were more than 70 years of age, 63% were female patients and 78.8% of the total costs were generated by female patients (£27 067) – this is attributable to the large proportion of extracolonic findings related to the female reproductive organs (Table 3). Nearly half (48.8%) of the total costs were generated by only 9 patients who were more than 80 years of age (the mean age of the patients with extracolonic findings who underwent further action was 74.6 years).
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Discussion |
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Not only may diagnostic studies yield different results from screening studies, but there may also be salient differences between one diagnostic study and another according to the population served, availability of CTC and perceptions of participating clinicians. For example, where CTC is a scarce resource, it is theoretically possible that clinicians will preferentially select patients for CT whose symptoms suggest extracolonic pathology. We should therefore consider the possibility that the population reported here contained a higher proportion of cases with symptoms triggering suspicion of non-bowel pathology than would be encountered should CTC more completely supplant other tests as the primary diagnostic method. We have a number of reasons for arguing that this potential bias did not significantly undermine the generalizability of our findings. First, the incidence of extracolonic lesions was similar in our series to that found in a systematic review [10] for diagnostic CTC (52% vs 46%). Second, most of the lesions found were at a very early stage (e.g. small abdominal aneurysms) or were of a long-standing nature (e.g. fibroids) [10]; and were therefore unlikely to have caused symptoms. Even the lesions that prompted surgery (see Table 1
) are generally silent – some notoriously so. Last, cases referred all had symptoms that prompted their referral to a specialist clinic for colorectal cancer and the incidence of colon cancer was high (14%), suggesting that clinicians were forecasting bowel pathology and were not (successfully) selecting out a sub-population whose symptoms pointed to non-bowel pathology. A randomized trial of CTC versus barium enema and CTC versus colonoscopy (the SIGGAR1 trial) [15] is currently underway. This multicentre study, which aims to recruit over 4000 patients by 2008, will provide more generalizable information since it is being conducted over many centres.
Costs of incidental lesions
The costs of managing incidental lesions (£150) appear high relative to the cost of the CTC itself. The cost of CTC is not given in the NHS costing manual, but this was computed at £103 by Nicholson [16] in his study comparing the costs of CTC with fibre optic colonoscopy. Furthermore, the cost of CTC computed for the SIGGAR1 trial was £120 to £150 [15]. By way of comparison, the cost of a barium enema is £68 [12] and it may be reasonable to conclude that the cost of colonography would be 2–2.5 times higher. This leads us to the conclusion that the costs contingent on finding incidental lesions are similar to, or greater than, those of the original colonographies themselves.
The further investigations and treatments recorded in Table 1 reflect the clinical judgement of individual clinicians. Some, such as the use of MRI rather than ultrasound to investigate, respectively, liver and ovarian lesions in patient numbers 27 and 37, might be regarded as unnecessarily elaborate. However, there are few really solid evidence-based guidelines to direct clinicians in these circumstances and our results reflect real world behaviour rather than the most parsimonious choice consistent with good practice.
Comparison with other studies
Several papers have reported the high prevalence of extracolonic findings found at CTC [10, 17], but only three studies (all from the USA) estimated the costs incurred by the clinical follow-up for extracolonic findings [7, 17, 18]. Based on Medicare reimbursement values these amounted to an additional $28, $28.12 and $34.33 per CT colonographic examination, respectively. The authors concluded that the cost of evaluating these lesions is low, since serious extracolonic diseases can be detected by CTC and the costs seemed justified. However, we estimated that the cost for follow-up of extracolonic findings was over 5 times higher. We have identified three reasons why our costs were higher. First, and of greatest importance, the costs evaluated in the American studies were related purely to investigations and excluded interventional procedures (e.g. endoscopy or surgery) and the associated inpatient stays. In our study, 87% of the total costs were generated by surgical treatments and their sequelae (Table 2). Second, the male–female ratios are different in these studies: 1.7:1 [7], 1.2:1 [18] and an all male population [17], respectively. The lower proportion of female patients may have led to more conservative estimates (in this study the male-female ratio was 1:1.5). Lastly, the median age was greater in our study (74 years) compared with 62–64 years in the American studies [11], which included many patients undergoing CTC for screening purposes [7, 17, 18].
Costs and savings not measured
We excluded costs for GP consultations, although in this series most further actions related to extracolonic findings were initiated by the hospitals rather than GPs (only two further actions were initiated by GPs). Including such costs would not materially affect our conclusions, since the unit cost of a GP consultation is a modest £20 [19].
The use of intravenous contrast enhancement with CTC was also reviewed in our original study [11]. 72% of patients received contrast. No complications due to contrast were recorded. The detection rate of extracolonic lesions was significantly higher when intravenous contrast was used (62% vs 24%), but it would be a mistake to infer cause and effect – the radiologist may be prompted to use contrast by the discovery of an incidental lesion or a colon cancer. In the latter case, CTC may actually save money by reducing the need for subsequent investigation. If all of the 31 patients with colon cancer would have been referred for a subsequent abdominal CT scan (with a unit cost of £49), had their diagnoses been made by other means, then this would have saved £1519. This would reduce the cost per patient from £153 to £146.
Implications
This study has found that the additional financial costs of further investigation and treatment of extracolonic lesions detected at CTC is approximately £150 per examination.
In addition to costs borne by the service (third party payer), there are also disadvantages for patients in discovering incidental extracolonic lesions – anxiety, financial loss, pain, morbidity and (very occasionally) death contingent on the discovery, investigation and treatment of the lesions. These side-effects and the health service costs must be offset against the good that may arise from early detection of potentially lethal diseases. The problem lies in estimating the number of life years saved on average as a result of detection of incidental lesions. We are unlikely to ever have a direct empirical estimate of the potential benefit attributable to detection of incidental lesions at CTC – the current (SIGGAR1) randomized trial [15] is too small by an order of magnitude to provide a direct measurement of long term benefits and harms arising from the detection of incidental lesions. Relevant information may emanate from the large trial of screening for prostate, lung, colon and ovary cancer (PLCO) [20] currently underway in the USA, but the data will not be directly transferable to a diagnostic population such as that described in this study.
Where direct estimates of a parameter are unavailable, modelling may provide a useful substitute. However, producing a full disease model to compute the benefits of detecting early cancer is very tricky and requires some almost heroic assumptions about such unknown parameters as lead-time bias and growth rate differences between a clinical and radiological population of tumours; a proportion of lesions may prove lethal even if they were detected early, while another proportion might not have proved lethal even if undetected. These proportions cannot be inferred from symptomatic populations because the biology of lesions at a particular stage may vary between symptomatic and screening populations. Instead of trying to produce a full blown model resting on very tenuous assumptions, we now offer a simple "thought experiment" as an aid to what must ultimately remain an informed judgement. We start by holding in abeyance, for the time being, considerations of the differences in cost-effectiveness of colonography versus other methods – after all, estimating these parameters is the main purpose of the SIGGAR1 trial. We will also put aside, for the moment, concerns about the inconvenience and morbidity of investigating and treating incidental extracolonic lesions. We then reverse the question, "Is it cost effective?" to ask, "How effective would it have to be to justify the costs?" The answer to the latter question is bounded by the relevant epidemiology and we therefore refer to this as the "headroom approach".
The most clinically significant extracolonic lesions detected were abdominal aortic aneurysms (over 5 cm) and early stage cancers (results from our primary study [11] and systematic review [10]). The detection rates of CTC for extracolonic N0M0 cancers and significant aneurysms are 2.5% and 1.7%, respectively, among symptomatic patients in our systematic review [10]. In our previous study [11] these figures were 0.4% and 2.7%. Combining our study with the systematic review yields percentages of 2.0% (95% confidence interval [CI] 1.0%, 2.9%) and 1.9% (95% CI 1.2%, 2.5%), respectively. Therefore, on average, we may expect about 4 (2–6) patients with early stage cancers and about 4 (2–5) with early stage aneurysms to be detected among every 200 people undergoing CTC. This sets the "headroom" for reduction of mortality, at least with respect to these two conditions. In England, the cost threshold for a healthy life year saved is about £30 000 [21]. The discovery of incidental lesions at a cost of £150 per person would be cost-effective if detection of these pre-clinical lesions resulted in at least 1 healthy life year saved per 200 investigations (150x200 = 30 000). The most common primary cancers detected incidentally by CTC are those of kidney and ovary [10], where there is a favourable survival advantage for treatment of earlier lesions [22]. It dose not seem implausible therefore (not-with-standing the biases mentioned above), that the investigation and treatment of incidental lesions may "pay their way". There may even be a little surplus to set against the side-effect of investigating and treating incidental lesions.
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Conclusion |
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This study was sponsored by the NHS Health Technology Assessment Programme as part of the SIGGAR1 trial. The "headroom approach" is a method TX, RL and others are developing for the MATCH (Multidisciplinary Assessment of Technology Centre for Health) EPSRC consortium. The views and opinions expressed are those of the authors and do not necessarily reflect those of the funders. We thank Dr Prakash Patil who provided help with the statistical analyses for this study.
Received for publication January 20, 2006. Revision received April 26, 2006. Accepted for publication May 8, 2006.
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