Overview
Prior Authorization is a payer's advance-review requirement for selected services. The provider submits clinical documentation before rendering care, and the payer either approves, modifies, denies, or requests additional information. Services commonly subject to PA include high-cost imaging (MRI, CT, PET), specialty pharmacy, durable medical equipment, elective surgery, behavioral health residential care, genetic testing, and site-of-service determinations that steer care to outpatient versus hospital settings.
The mechanism exists to enforce three distinct payer policies: medical necessity under the plan's coverage guidelines, formulary or network steerage, and site-of-service optimization. While the stated intent is utilization management, prior authorization is consistently ranked by physicians as the highest administrative burden in US healthcare. The AMA's annual Prior Authorization Physician Survey has for multiple years reported that a large majority of physicians describe PA burden as "high" or "extremely high," with survey respondents estimating more than 40 authorization requests per physician per week and multiple hours of clinical staff time consumed daily.
The workflow spans three touchpoints. Determining whether a service requires PA — the payer PA list is updated quarterly by most plans, monthly by some, and varies by line of business (commercial vs. Medicare Advantage vs. Medicaid MCO). Submitting the request with clinical documentation sufficient to support medical necessity under the payer's applicable clinical policy. And tracking the authorization number, approved units, approved service dates, and approved CPT codes so the claim can be billed in alignment with what was approved.
Failure at any of the three touchpoints produces CARC 197 (precertification/authorization/notification absent) or CARC 198 (precertification/authorization exceeded) on the 835 remittance. These denials are among the hardest to recover because the service has already been rendered — the appeal relies on retroactive authorization or demonstrating emergent medical necessity under the plan's exception language.
Electronic prior authorization standards exist but adoption has been uneven. X12 278 is the HIPAA-mandated transaction for authorization requests and responses, but many payers still require portal submissions or faxes for clinical attachments. CMS regulations — specifically the Interoperability and Prior Authorization Final Rule (CMS-0057-F) — require impacted payers to implement FHIR-based prior-authorization APIs (PAS/CRD/DTR) and to publish metrics including PA approval rate, denial rate, and turnaround time by 2027. Practices tracking outbound authorizations should currently measure approval rate, average turnaround days, percent submitted before date of service, and the rate of PA-related denials as leading indicators.
Operationally, the most effective PA programs move authorization determination to scheduling — before the patient is even given an appointment time. Integrating the scheduling system with a payer rules engine catches PA-required services at the earliest point; obtaining authorization at scheduling reduces downstream denial risk by an order of magnitude and avoids same-day rescheduling.
Industry benchmark
AMA's 2023 Prior Authorization Physician Survey reports that 94% of physicians say PA delays patient care and that physicians complete an average of 43 PAs per week. CMS's Interoperability and Prior Authorization Final Rule (CMS-0057-F) sets a 2027 deadline for FHIR-based electronic PA APIs for most impacted payers.
Worked example
A patient is scheduled for an outpatient MRI on Tuesday. The payer's PA list requires precertification for advanced imaging. The scheduler's integrated PA rules engine flags the appointment, the prior-auth team submits a 278 request with the ordering physician's clinical justification, and approval arrives in 36 hours with an authorization number valid for 30 days. The claim bills with the authorization number and avoids a CARC 197 denial.
Frequently asked questions — Prior Authorization
What services typically require prior authorization?
Advanced imaging (MRI, CT, PET), specialty medications, durable medical equipment, most elective surgeries, behavioral health inpatient or residential care, genetic testing, and site-of-service determinations are the most common. The specific list varies by payer, plan, and line of business, and is updated quarterly by most payers.
What is the difference between prior authorization and precertification?
The terms are used interchangeably by most payers in the US. Historically some plans distinguished precertification (notification) from prior authorization (clinical review), but in current practice the workflows are identical and the terms are synonymous.
How long does prior authorization take?
Standard commercial requests are decided within 3–5 business days; urgent requests typically within 72 hours or less. Medicare Advantage rules under CMS-4201-F require 7 calendar days for standard and 72 hours for expedited. Actual payer turnaround times vary — track it as a monthly KPI.
What happens if a service is performed without required prior authorization?
The claim is typically denied under CARC 197. Recovery requires a retroactive authorization request or an appeal citing emergent medical necessity. Approval rates on retroactive requests are materially lower than on prospective requests, which is why PA workflow should be triggered at scheduling rather than after service.
Disclaimer
This glossary entry is operational reference for revenue-cycle and medical-billing professionals. It is not legal, clinical, or contractual advice. Industry benchmarks cite named public sources where available; always verify against the current guidance from the authority body before relying on a number in a contract, policy, or compliance filing.