Finding cancer in primary care outpatients with low back pain - A comparison of diagnostic strategies

OBJECTIVE: To compare strategies for diagnosing cancer in primary care pati ents with low back pain. Strategies differed in their use of clinical findi ngs, erythrocyte sedimentation rate (ESR), and plain x-rays prior to imagin g and biopsy. DESIGN: Decision analysis and cost effectiveness analysis with sensitivity analyses. Strategies were compared in terms of sensitivity, specificity, an d diagnostic coat effectiveness ratios. SETTING: Hypothetical. MEASUREMENTS: Estimates of disease prevalence and test characteristics were taken from the literature. Costs were represented by the Medicare reimburs ement for the tests and procedures employed. MAIN RESULTS: In the baseline analysis, using magnetic resonance imaging (M RI) as the imaging procedure prior to a single biopsy, strategies ranged in sensitivity from 0.40 to 0.73, with corresponding diagnostic coats of $14 to $241 per patient and average cost effectiveness ratios of $5,283 to $49, 814 per case of cancer found. Incremental cost effectiveness ratios varied from $8,397 to $624,781; five strategies were dominant in the baseline anal ysis. Use of a higher ESR cutoff point (50 mm/hr) improved specificity and cost effectiveness for certain strategies, Imaging with MRI, or bone scan f ollowed in series by MRI, resulted in fewer unnecessary biopsies than imagi ng with bone scan alone. Cancer prevalence was an important determinant of cost effectiveness. CONCLUSIONS: We: recommend a strategy of imaging patients who have a clinic al finding (history of cancer, age greater than or equal to 50 years, weigh t loss. or failure to improve with conservative therapy) in combination wit h either an elevated ESR (greater than or equal to 50 mm/hr) or a positive x-ray, or using the same approach but imaging directly those patients with a history of cancer.