Characteristics of diagnostic tests

Medical decisions are taken in a framework of uncertainty. Probability of disease moves between diagnostic threshold, below which no further tests are needed, and therapeutic threshold, above which we don’t need further tests to justify treatment. Sensitivity and specificity are intrinsic properties of diagnostic tests that provide us with their ability to discriminate between healthy and sick people. Predictive values inform us about the probability that a positive patient is ill or that a negative patient is healthy, and they are used with people with unknown disease status. Finally likelihood ratios give us the actual probability of having the disease if we know pre-test probability and the result of the test.