What does rule out mean in medical terms?

"Rule out" is another term for differential diagnosis. The differential is a list of possible conditions that could explain the patient's symptoms. Through continued history, exam, and lab/imaging studies, the clinician narrows the differential to come to a diagnosis. When reading "rule out" in a medical narrative, you can replace the phrase with the Words "make sure it's not." So the phrase "chest pain, rule out myocardial infarction" can be read as "chest pain, make sure it's not a heart attack."

differential diagnosis.