Determining Medical Necessity in the ER & Observation Setting

(CMS-Defined Requirements – Hospital Outpatient Services)

Under CMS policy, medical necessity is the controlling factor for whether hospital outpatient services—including Emergency Department (ED) and Observation services—are payable. CMS evaluates medical necessity based on the patient’s condition and the services furnished, as documented in the medical record.

CMS makes clear that payment is not based on the label of the service, but on whether the services were reasonable and necessary for diagnosis or treatment of illness or injury.

A. Medical Necessity for Emergency Department Services (CMS Perspective)

CMS does not define ED medical necessity by diagnosis alone. Instead, CMS evaluates whether:

• The patient’s presenting signs and symptoms required hospital emergency resources

• The services furnished were reasonable and necessary given the patient’s condition

• The level of hospital resources used is supported by documentation

CMS-Supported Documentation To Determining Medical Necessity

According to Chapter 12, ED services must be supported by documentation that demonstrates:

• Presenting symptoms or condition at the time of arrival

• The need for evaluation and treatment in an emergency setting

• The services actually furnished by hospital staff

CMS explicitly recognizes that:

Medical necessity must be determined based on the patient’s condition at the time of presentation, not the final diagnosis.

This means documentation must reflect:

• Why the patient required emergency-level care

• Why outpatient clinic or delayed care would not have been appropriate

B. Medical Necessity for Observation Services (CMS-Specific Requirements)

CMS places significantly stricter requirements on observation services than on ED visits.

CMS Definition of Observation Services

CMS defines observation as:

A well-defined set of specific, clinically appropriate services, which include ongoing short-term treatment, assessment, and reassessment, that are furnished while a decision is being made regarding whether a patient will require further treatment as a hospital inpatient or can be discharged.

Observation is not:

• A substitute for inpatient admission

• A holding status

• A convenience designation

CMS Documentation Requirements for Observation Medical Necessity

To support observation services, the medical record must show:

1. A physician order for observation services

   • Must be explicit

   • Must be timed and authenticated

2. Clinical uncertainty

   • The patient’s condition requires monitoring or evaluation

   • A decision regarding admission or discharge cannot yet be made

3. Active assessment and management

   • Ongoing evaluation

   • Monitoring of response to treatment

   • Continued clinical decision-making

CMS states that observation services are only payable when:

There is a reasonable expectation that the patient’s condition can be evaluated or treated within a short period of time.

CMS does not allow observation billing when documentation shows only routine monitoring or bed availability delays.

C. CMS Relationship Between Medical Necessity & Payment

CMS policy is clear:

• Services that are not medically necessary are not payable

• Time alone does not establish medical necessity

• Orders without supporting documentation do not justify payment

Medical necessity is the gatekeeper for:

• ED visit payment

• Observation hour payment

• Ancillary outpatient services

4. ED Facility Level Determination

(CMS-Allowed Framework for Hospital Resource Reporting)

CMS does not prescribe a national methodology for determining ED facility visit levels. However, CMS establishes strict principles that hospitals must follow.

A. CMS Position on ED Facility Levels

CMS allows hospitals to:

• Develop their own ED visit level criteria

• Assign levels based on hospital resource usage

However, CMS requires that the methodology be:

• Consistently applied

• Clinically reasonable

• Auditable

• Based on services furnished, not physician judgment

CMS explicitly states that:

ED visit levels must reflect the hospital resources required to furnish the care, as documented in the medical record.

B. Documentation CMS Expects to Support ED Facility Levels

CMS evaluates ED levels based on documentation that reflects:

1. Hospital Staff Interventions

• Nursing services

• Technical services

• Monitoring

• Treatments provided

These services must be:

• Clearly documented

• Time-linked when applicable

• Within scope of outpatient hospital services

2. Intensity of Hospital Resource Use

CMS supports higher ED levels when documentation shows:

• Multiple hospital resources

• Increased monitoring

• More complex nursing care

• Greater patient instability

CMS does not allow ED levels to be based on:

• Physician medical decision-making

• CPT professional E/M rules

• Diagnosis alone

• Length of stay by itself

3. Internal Consistency Requirement

CMS requires that:

• Similar patients receive similar ED levels

• Documentation supports the same resource intensity for the same level

• Hospitals avoid subjective or variable level assignment

This is a major audit focus under CMS medical review.

If a service is not clearly documented, CMS considers it not furnished.