It is impossible to determine from a discharge diagnosis or a chief complaint who has an emergency medical condition and who can be seen later in another setting.  We can all recount stories of someone triaged as at a low level and was determined by the physician to have require emergency surgery or have a life threatening condition.  This article in JAMA found that nearly 5% of patients determined to be non-emergent were admitted to the hospital.

This study uses data from the National Hospital Ambulatory Medical Care Survey to examine whether a triage determination of nonurgent status in the emergency department ruled out the possibility of serious pathologic conditions, as compared with visits deemed as urgent.

Source: JAMA Network | JAMA Internal Medicine | Urgent Care Needs Among Nonurgent Visits to the Emergency Department