20 Miss. Code R. § 2-VIII
Emergency department (ED) service codes do not differentiate between new and established patients and are used by hospital-based and non-hospital-based physicians. An emergency department is defined as "an organized hospital-based facility for the provision of unscheduled episodic services to patients who present for immediate medical attention. The facility must be available 24 hours a day." This guideline indicates that care provided in the ED setting for convenience should not be coded as an ED service. Also note that more than one ED service can be reported per calendar day if medically necessary.
Codes 99281-99288 are used to report services provided in a medical emergency. If, however, the physician sees the patient in the emergency room out of convenience for either the patient or physician, the appropriate office visit code should be reported (99201-99215) and reimbursement will be made accordingly.
20 Miss. Code. R. § 2-VIII