Rule out (R/O)
Formal Definition
To use clinical evaluation, diagnostic testing, or observation to exclude a specific diagnosis from consideration. A patient admitted to "rule out" a condition is being monitored and tested to determine whether the diagnosis applies.
How It's Used on the Ward
"R/O PE" or "ruling out ACS" — the patient hasn't been diagnosed yet; workup is in progress to confirm or exclude.
Example
""43-year-old with pleuritic chest pain and recent long-haul flight — admit to telemetry to rule out PE. CT pulmonary angiogram ordered, heparin held until result.""
Clinical Context
Technically, you "rule in" a diagnosis (confirm it) or "rule out" (exclude it). In practice, "I'm ruling out PE" often means "I suspect PE and am testing." Understand which diagnostic tests have high negative predictive value for ruling out (e.g., D-dimer + Wells score to exclude PE) vs. which are used to rule in.
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