Quick Answer: Prior authorization (PA) is a requirement by insurance payers that providers obtain approval before delivering certain services, procedures, or medications. Without it, claims are denied — even if the treatment is medically necessary. It is one of the most common causes of claim denials and revenue loss in healthcare practices.

Prior authorization is among the most time-consuming administrative burdens in modern healthcare. In fact, a 2023 AMA survey found physicians complete an average of 45 prior authorization requests per week, with each taking nearly 12 minutes of physician time and significantly more for staff. For small and mid-size practices, that’s dozens of hours per month spent seeking permission before treating patients.
This guide explains exactly how prior authorization works, when it’s required, why it leads to denials, and what your billing team can do to reduce approval delays.

What Is Prior Authorization in Medical Billing?

Prior authorization — also called pre-authorization, pre-approval, or prior approval — is a process where a healthcare provider must get advance approval from a patient’s insurance company before performing a specific service, procedure, or prescribing certain medications.

Insurers use it to:

Confirm the service is medically necessary         Verify the patient’s plan covers the service

Ensure cost-effective alternatives have been considered

Common services that typically require prior authorization:

Elective surgeries (joint replacements, bariatric procedures) MRI, CT scans, and advanced imaging

Specialty medications and biologics Durable medical equipment (DME) Inpatient admissions and transfers Home health services

Physical, occupational, and speech therapy (beyond initial visits) Behavioral health and substance use treatment

How Does the Prior Authorization Process Work? (Step by Step)

Step 1: Identify Whether PA Is Required

Before scheduling or ordering, check the patient’s insurance plan requirements. This is done through payer portals, eligibility verification, or calling the payer directly. Missing this step is the #1 reason for avoidable denials.

Step 2: Gather Clinical Documentation

The payer will require medical records, physician notes, diagnosis codes (ICD-10), procedure codes (CPT/HCPCS), and often a Letter of Medical Necessity (LMN) explaining why the service is appropriate for this patient.

Step 3: Submit the PA Request Requests are submitted via:

Payer web portals (most common and fastest)      Electronic submission via clearinghouses

Fax (still required by some payers)

Phone (used for urgent/emergent cases)

Step 4: Payer Review

The payer reviews the request against clinical guidelines (usually InterQual or MCG criteria). Review can be done by a nurse, pharmacist, or physician depending on complexity.

Step 5: Decision Is Issued

The payer issues one of three responses:

Approved — claim can proceed

Denied — service not approved; provider must appeal or seek alternatives

Pending — more information requested; provider must respond within a deadline

Step 6: Proceed or Appeal
If approved, the authorization number must be documented and included on the claim. If denied, the provider can file a peer-to-peer review request or formal appeal.

How Long Does Prior Authorization Take?

under the CMS Interoperability and Prior Authorization Rule (finalized 2024), most payers must now respond to standard PA requests within 7 calendar days and expedited requests within 72 hours — a significant improvement from historical timelines.
Top Reasons Prior Authorization Gets Denied

1. Missing or insufficient clinical documentation — Most common reason; notes don’t support medical necessity
2. Service not covered under the patient’s plan — PA granted but plan exclusion applies
3. Wrong procedure or diagnosis code — Code mismatch with the requested service
4. Step therapy not followed — Payer requires trying a lower-cost treatment first
5. Out-of-network provider — PA submitted but provider not in-network
6. Expired authorization — Service performed after the PA authorization window closed
7. Duplicate request — PA already exists for the same service/date range

What Happens If You Don’t Get Prior Authorization?

If a service requiring PA is performed without obtaining authorization first:

The claim will be denied upon submission

The provider cannot bill the patient for the denied amount in most cases (balance billing rules)

The practice absorbs the loss unless a successful appeal reverses the denial Repeated PA failures can trigger payer audits

In short: no auth = no payment.

How to Reduce Prior Authorization Denials: 7 Best Practices

1. Verify requirements before every appointment — Use payer portals or automated eligibility tools at the time of scheduling, not just day-of-service
2. Build a PA tracking log — Track submission dates, payer reference numbers, expiration dates, and follow-up deadlines
3. Train clinical staff on documentation standards — Denials for medical necessity are almost always a documentation problem, not a clinical one
4. Know each payer’s clinical criteria — InterQual and MCG guidelines differ by payer; know what each one requires before submitting
5. Submit peer-to-peer reviews promptly — When a PA is denied, a physician-to-physician call can overturn ~30–40% of denials; deadlines are tight (often 24–48 hours)
6. Use electronic PA submission — Reduces turnaround time compared to fax/phone
7. Partner with a specialized billing team — Practices that outsource PA management see significantly lower denial rates due to dedicated, trained staff

Prior Authorization vs. Pre-Certification vs. Referral: What’s the Difference?

Frequently Asked Questions

Can prior authorization be retroactive?

In emergency situations, most payers allow retroactive authorization requests, typically within 24–72 hours of service. Non-emergency retro requests are almost always denied.

Does prior authorization guarantee payment?

No. Authorization confirms the service is covered and approved — it does not guarantee the claim will be paid. Claim submission errors, eligibility issues, or coding mistakes can still result in denial after PA is granted.

Who is responsible for getting prior authorization — the provider or the patient?

The provider’s billing or authorization team is responsible for submitting the PA request. Patients should not be required to manage this process.

What is the difference between a PA denial and a claim denial? A PA denial occurs before service is rendered. A claim denial occurs after the claim is submitted. Both require different appeal processes.

The Bottom Line

Prior authorization is a necessary but burdensome part of modern medical billing. Practices that master the PA process — through clear workflows, dedicated staff, accurate documentation, and proactive follow-up — experience fewer delays, less revenue leakage, and better patient outcomes.

If your practice is struggling with prior authorization backlogs or denial rates above 5%, it may be time to evaluate your current process or partner with a specialized revenue cycle management team.