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Finding cancer in primary care outpatients with low back pain: a comparison of diagnostic strategies |
Joines J D, McNutt R A, Carey T S, Deyo T A, Rouhani R |
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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 Strategies for diagnosing cancer in primary care patients with low back pain. The strategies, and their relevant technologies, were as follows: B = MRI (image) if erythrocyte sedimentation rate positive(ESR+) and x-ray positive; C = image everyone; D = image if ESR positive; E = image if x-ray positive; F = image if ESR positive and x-ray positive; B2; D2; E2 and F2 which were identical to B, D, E and F except that patients with a history of cancer (HxCa) would proceed directly to MRI imaging. These strategies were followed prior to imaging and possible biopsy, making eleven plausible diagnostic procedures.
Economic study type Cost-effectiveness analysis.
Study population The study population was a hypothetical cohort of primary care outpatients with low back pain.
Setting The hypothetical setting was secondary care; the economic study was conducted in the USA.
Dates to which data relate Effectiveness and resource use data were collected from studies published between 1963 and 1998. 2000 cost data and price data were used.
Source of effectiveness data Effectiveness data were derived from a literature review.
Modelling A decision tree was used to model the cost-effectiveness of diagnostic strategies.
Outcomes assessed in the review The review assessed clinical findings and the sensitivity and specificity of diagnostic tests.
Study designs and other criteria for inclusion in the review Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Summary statistics from individual studies were used.
Number of primary studies included At least 21 primary studies were included.
Methods of combining primary studies Primary studies were combined using the narrative method.
Investigation of differences between primary studies Results of the review Four predictors of cancer in patients with low back pain were used: a previous history of cancer, age exceeding 50 years, a failure to improve with conservative therapy, and unexplained weight loss.
ESR of 20 or more had a sensitivity of 0.78 and a specificity of 0.67.
ESR of 50 or more had a sensitivity of 0.56 and a specificity of 0.97.
Lumbosacral x-ray had a sensitivity of 0.70 and a specificity of 0.95.
MRI had a sensitivity of 0.95 and a specificity of 0.95.
Bone scan had a sensitivity of 0.95 and a specificity of 0.70.
A single biopsy under fluoroscopic guidance had a sensitivity of 0.85 and a specificity of 1.00. The authors assumed no biopsy complications.
Measure of benefits used in the economic analysis The number of cancers found was used as the measure of benefits.
Direct costs Direct costs were not discounted as the time horizon was less than 1 year. Quantities and costs were reported separately. Direct costs included the costs of tests and procedures employed. The quantity/cost boundary adopted was that of the health service. The estimation of quantities and costs was based on actual data. Costs were based on reimbursement data. The price year was 2000.
Statistical analysis of costs No statistical analysis of costs was reported.
Indirect Costs Indirect costs were not included.
Sensitivity analysis Sensitivity analyses were conducted on cancer prevalence, MRI sensitivity, costs of testing, the use of low or high estimates of the sensitivity and specificity of the clinical findings, and the effect of imaging with bone scan alone or bone scan followed in series by MRI.
Estimated benefits used in the economic analysis Strategy sensitivity ranged from 0.4 for image if ESR was positive and x-ray positive to 0.732 for image everyone. Strategy specificity ranged from 0.9997 to 0.9794. A total of 3.4 to 26.1 biopsies per 1,000 patients were performed to find 2.6 to 4.8 cases of cancer.
Cost results Diagnostic costs per patient ranged from $14 to $241.
Synthesis of costs and benefits Average cost-effectiveness ranged from $5,283 to $49,814 per case of cancer found, and incremental cost-effectiveness ranged from $8,397 to $624,781. The dominant strategies in order of increasing effectiveness were image if ESR+ and x-ray+, selective testing, image if HxCa+ or x-ray+, image if HxCa+ or ESR+ or x-ray+, and image everyone. Use of a higher ESR cut-off point (50 mm/hr) improved the specificity and cost-effectiveness for certain strategies. Imaging with MRI or bone scan followed in series by MRI resulted in fewer unnecessary biopsies than imaging with bone scan alone. Cancer prevalence was an important determinant of cost-effectiveness.
Authors' conclusions The authors recommended a strategy of imaging patients who have a clinical finding (previous history of cancer, age exceeding 50 years, failure to improve with conservative therapy, and unexplained weight loss) in combination with either an elevated ESR (> 50 mm/hr) or a positive x-ray, or using the same approach but imaging directly those patients with a history of cancer.
CRD COMMENTARY - Selection of comparators A justification was given for the comparators used, namely clinically plausible diagnostic strategies. The reader should decide if these health technologies are relevant to his or her setting.
Validity of estimate of measure of effectiveness The authors undertook a literature review to derive estimates for the decision tree, which seemed appropriate, although they did not state that a systematic review of the literature had been undertaken. More information about the methods of the review would be necessary in order to make an objective assessment. However the validity of results was enhanced by sensitivity analyses to account for variability in the estimates. However, the sensitivities of the clinical findings used in the study were estimated from small numbers of patients and therefore had wide confidence intervals. Moreover, because spinal malignancy includes a diverse group of neoplasms, the test characteristics may not be uniformly applicable.
Validity of estimate of measure of benefit The estimation of benefits was obtained directly from the effectiveness analysis. The authors did not quantify patient concern, inconvenience, and the discomfort of unnecessary biopsies in the analysis, nor did they consider utilities associated with treatment outcomes. The authors only considered an intermediate outcome (cases of cancer found). Future analyses over a longer time frame would be informative.
Validity of estimate of costs Good features of the cost analysis were that all relevant direct cost categories were included. Quantities and costs were reported separately, and the price year was reported. The validity of cost results was further enhanced by appropriate sensitivity analyses over plausible ranges. However, charges were used to proxy prices, which do not represent opportunity costs. In addition, the costs of treatment and the costs associated with missed diagnoses of cancer were not included. The authors also excluded the costs of any additional testing or therapy associated with incidental abnormalities found on MRI scanning. These issues were comprehensively discussed and commented upon by the authors.
Other issues The authors did make appropriate comparisons of their findings with those from other studies and also addressed the issue of generalisability to other settings. The authors did not present their results selectively. The study considered primary care outpatients with low back pain over the diagnostic phase of managing this group, and this was reflected in the authors' conclusions.
Implications of the study The authors recommended a strategy of imaging patients who have a clinical finding (previous history of cancer, age exceeding 50 years, failure to improve with conservative therapy, and unexplained weight loss) in combination with either an elevated ESR (> 50 mm/hr) or a positive x-ray, or using the same approach but imaging directly those patients with a history of cancer.
Source of funding Partially supported by the North Carolina Back Pain Project (Agency for Health Care Policy and Research Grant HS06664), the Back Pain Outcome Assessment Team (Agency for Health Care Policy and Research grants HS06344 and HS08194), and National Research Service Award 5-T32-PE-14001) from the Health Resources and Services Administration through the Primary Care Research Fellowship Program of the University of North Carolina.
Bibliographic details Joines J D, McNutt R A, Carey T S, Deyo T A, Rouhani R. Finding cancer in primary care outpatients with low back pain: a comparison of diagnostic strategies. Journal of General Internal Medicine 2001; 16(1): 14-23 Indexing Status Subject indexing assigned by NLM MeSH Aged; Biopsy /economics; Humans; Low Back Pain /complications /diagnosis; Magnetic Resonance Imaging; Middle Aged; Outpatients; Spinal Neoplasms /complications /diagnosis /economics AccessionNumber 22001000448 Date bibliographic record published 31/10/2001 Date abstract record published 31/10/2001 |
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