How to interpret diagnostic tests.

Healthcare professionals make decisions in a context of uncertainty. When making a diagnosis, relevant patient characteristics are categorized to fit a particular condition that explains what the patient is experiencing. During the diagnostic process, tools such as the medical interview, physical examination, and other complementary tests support this categorization.

These tools, known as diagnostic tests, allow professionals to estimate the probability of the presence or absence of the suspected medical condition. The usefulness of diagnostic tests varies for each clinical condition, and studies of accuracy (sensitivity and specificity) and diagnostic impact (impact on health outcomes) are used to evaluate them. In this article, the general theoretical and practical concepts about diagnostic tests in human beings are addressed, considering their historical background, their relationship with probability theories, and their practical utility with illustrative examples.