EBM NOTEBOOK

Coronary artery disease (CAD) exists in a spectrum: it ranges from the early lesions seen in young victims of trauma1 through to sudden cardiac death or myocardial infarction with cardiogenic shock. Yet diagnostic studies that compare the clinical features and diagnostic tests with a reference standard usually act as if the disease was a homogeneous entity. This dichotomous approach to diagnostic accuracy is measured as sensitivity and specificity, likelihood ratios, diagnostic odds ratios, and the area under the receiver-operator characteristic curve.2 Ransahoff and Feinstein recognised that “unless an appropriately broad spectrum is chosen for the diseased and non-diseased patients who comprise the study population,” the diagnostic test may result in spurious estimates of diagnostic performance.3 However, this article argues that it is not possible to have a sufficiently broad spectrum of patients to be of value in a single description of diagnosis, prognosis, and therapy of any common condition such as CAD.

The clinical and diagnostic features of disease such as CAD change with increasing severity of the disease. Generalists, particularly primary care clinicians, are likely to see less severe manifestations of CAD than specialists. Hence, depending on the level of specialisation of the clinician, disease presentation may create spurious clinical associations or miss legitimate clinical associations.

The solution proposed for this differing disease presentation in different clinical contexts is to recognise that …