ANALYSIS OF PROBABILITY AS AN AID IN THE CLINICAL-DIAGNOSIS OF CORONARY-ARTERY DISEASE

The diagnosis of coronary-artery disease has become increasingly complex. Many different results, obtained from tests with substantial imperfections, must be integrated into a diagnostic conclusion about the probability of disease in a given patient. To approach this problem in a practical manner, we reviewed the literature to estimate the pretest likelihood of disease (defined by age, sex and symptoms) and the sensitivity and specificity of four diagnostic tests: stress electrocardiography, cardiokymography, thallium scintigraphy and cardiac fluoroscopy. With this information, test results can be analyzed by use of Bayes’ theorem of conditional probability. This approach has several advantages. It pools the diagnostic experience of many physicians and integrates fundamental pretest clinical descriptors with many varying test results to summarize reproducibly and meaningfully the probability of angiographic coronary-artery disease. This approach also aids, but does not replace, the physician's judgment and may assist in decisions on cost effectiveness of tests. (N Engl J Med 300:1350–1358, 1979) THE diagnosis of coronary-artery disease on the basis of history and physical examination alone is often difficult. Many sophisticated tests have thus been developed to allow an early and more accurate diagnosis. Although many tests are now firmly established in clinical practice, none is particularly suited to wide-scale, cost-effective application,1 because each has limitations concerning sensitivity and specificity. Thus, when a positive test result occurs in a patient with a low likelihood of disease, it is of limited diagnostic importance.2 3 4 A “positive” electrocardiographic stress test in an asymptomatic patient, for example, has a predictive accuracy of only 30 per cent. © 1979, Massachusetts Medical Society. All rights reserved.