The New England journal of medicine
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The sensitivity and specificity of the hypertensive intravenous pyelogram and the iodohippuran renogram have been determined for the diagnosis of renovascular disease, and cost-effectiveness calculations have been made for the diagnosis and surgical treatment of patients with renovascular hypertension. When the intravenous pyelogram alone is used to screen representative hypertensive population, 78 per cent of patients with renovascular disease are located, but at the same time an equal number of patients without renovascular diasease have abnormal pyelograms. The renogram, on the other hand, is associated with varying true-positive and false-positive ratios. ⋯ The cost of finding a patient with renovascular disease is about $2,000, and that of a surgical cure is about $20,000. The number of deaths for 100 surgical cures is approximately 15. The dollar cost of screening and treating the total American renovascular hypertensive population is of the order of 10 to 13 billion dollars.
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The value of a diagnostic test lies in its ability to detect patients with disease (its sensitivity) and to exclude patients without disease (its specificity). For tests with binary outcomes, these measures are fixed. For tests with a continuous scale of values, various cutoff points can be selected to adjust the sensitivity and specificity of the test to conform with the physician's goals. Principles of statistical decision theory and information theory suggest technics for objectively determining these cutoff points, depending upon whether the physician is concerned with health costs, with financial costs, or with the information content of the test.
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An attempt was made to discover the difference in outcomes between treating all patients with essential and renovascular hypertension by drug therapy independent and ignorant of etiologic classification and identifying the patients with renovascular disease and operating on them. Outcomes were categorized as well without complications of hypertension, alive but suffering from a related morbid illness such as coronary or cerebral arterial disease, and dead from the complications of diagnosis, surgery or high blood pressure. The identification and surgical treatment of hypertensive renovascular disease resulted in an incremental benefit in morbidity over blind antihypertensive medical therapy only when the compliance with medical treatment was about 50 per cent or less (the rate suggested for most patient populations). The study underscores the extent to which the quantitative efficacy of diagnositc and therapeutic procedures depends not only on the inherent risks and benefits but also on related social and medical factors.
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The six sequential stool guaiac protocol has been advocated for screening of colonic cancer. Analysis of the expenditures involved in such a program shows that the cost of detecting cancer rises exponentially so that the marginal cost of the sixth test may be 20,000 times the average cost. ⋯ This result shows that even an inexpensive test can become quite costly in terms of cases detected. The marginal cost per case detected depends on the prevalence of the condition in the population screened and the sensitivity of the test applied.