Differential

Differential diagnosis is the iterative process of developing and testing possible explanations for a patient's health problem. The goal is a correct, timely explanation that fits the whole presentation and leads to safe action. The working diagnosis may change as new history, examination findings, test results, treatment response, or changes in trajectory become available. Start with a compact problem representation: who the patient is, what changed, how quickly it changed, the most discriminating positive and negative findings, and the relevant risks. Then ask which diagnosis is most likely, which dangerous diagnosis remains plausible, and what finding or test would move each possibility up or down the list. Rank both probability and consequence of delay. A result has meaning only in context. Before ordering a test, identify the question it is intended to answer and what action will follow a positive, negative, or indeterminate result. Interpret the result with the pretest probability, timing, assay or imaging limitations, and the patient's current stability. A negative result obtained too early, in the wrong population, or with an inapplicable decision rule does not safely...