When you hear hoof beats: four principles for separating zebras from horses

When a patient comes to the clinic with a new complaint, the often wide array of possible causes creates uncertainty about the optimal evaluation and treatment. Selecting an approach to evaluation involves values that range from ruling out all disease processes (all zebras) regardless of cost to limiting cost by looking only for those processes that are likely (assuming all hoof beats are created by horses). Neither extreme is an optimal approach. We do not want to spend money on unnecessary tests, but we also do not want to miss a rare but potentially serious and treatable disease.

We offer four principles and their accompanying corollaries that make it possible to separate more easily hoof beats for horses from those for zebras.

By applying these principles and the accompanying corollaries, a physician can more efficiently determine the most efficient and cost-effective approach to taking care of patients.