A utilization control measure employed by PPO, EPO, HMO and POS plans, whereby, elective hospital admissions or other expensive medical services or procedures must be approved by the insurance company, medical group, gatekeeper or primary care physician in advance. Such advance approval is known as prior authorization and is based on the insurance companies determination of medical necessity, appropriateness and other pertinent factors. Generally surgeries require prior authorization as do many procedures and tests done in the physician's office. A utilization review or prior authorization phone number is usually available from the insurance company to request authorization. For all emergency surgeries and admissions the provider must notify the insurance carrier of the patient's admission within 24 hours.