(Last Updated On: March 14, 2017)Inigo Montoya - Rule out I do not think it means what you think it means

Chapter 10 – “Rule Out”

Welcome to the tenth installment of “Inconceivable: medical terms that don’t mean what you think they mean.”

You are evaluating a young, healthy woman on OCP who presents to the ED for pleuritic chest pain. Her chest x-ray, EKG, and labs are all normal. You document that her d-dimer was <0.5 mg/dl and therefore “pulmonary embolism is ruled out.” Are you confident in that sentence?  As emergency physicians – like most other arenas in medicine – we rarely rule anything out. Confused? Intrigued? Read on.

The phrase “rule out” means to exclude, eliminate, or make impossible. Despite all the advances in modern medicine, very few tests truly exclude anything, instead they risk stratify. Every lab test, imaging study, and decision tool has a sensitivity and a specificity. There is no perfect test in medicine although some are close. Look at the list below for some commonly used tests and their respective sensitivities (ability to rule out a diagnosis).

  • Urine pregnancy test – 98% (3 days after missed menses), 100% (7 days after missed menses)
  • PERC for PE – 97%
  • D-dimer for PE – 99% (in non-high risk patients)
  • CT PA for PE – about 90% (depends on the scanner, image quality, and radiologist)
  • CT for appendicitis – 93%
  • CT for kidney stone – virtually 100%
  • HEART score + troponin x2 for ACS – 99%

Every one of these tests has a certain “miss rate,” and obviously, some are more sensitive than others. Your testing may have stratified the risk to such a low number that further testing or evaluation is irresponsible, and that’s often our goal in the ED.

The concept of risk stratification is more important than just being precise with language; remain mindful of this concept when caring for patients.  No matter what testing you’ve done, you’ve rarely ruled anything out. Instead, you have risk stratified your patient with regards to a diagnosis, etiology, or pathology.



Be careful throwing around the term “rule out,” both in your discussions with consultants and your documentation. Remember, we don’t rule things out, we risk stratify. Adjust your communication and thought process accordingly.



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Dr. Krueger (@HoyaBadger) is currently an emergency medicine attending physician at Advocate Lutheran General Hospital, clinical instructor at UIC, and a former UIC EM Chief Resident.