Equation and nomogram for calculation of testing and treatment thresholds.

To the Editor.-According to the threshold model, the choice of a particular clinical strategy, observation vs testing vs treatment, is dictated by the probability of disease’s exceeding two relevant threshold probabilities.* If the probability of disease is below the testing threshold (p,l, testing should be withheld. If the probability of disease is above the treatment threshold (p,), then treatment should be given. The test should be performed only if the probability of disease is between the two thresholds. These threshold probabilities can be calculated from the data on the benefits and risks of the appropriate treatments, the sensitivity and specificity of a particular diagnostic test, and the risks associated with the test.’ We further generalize this model by providing an equation for calculation of any threshold probability*: