Authorization in Medical Billing: The Complete Guide to Getting It Right Every Time

One of the most common and preventable reasons for claim denials in U.S. healthcare is a missing or incorrect prior authorization. Authorization in medical billing is the process of obtaining advance approval from a health insurance plan before delivering specific medical services, procedures, or prescription drugs.

It sounds straightforward. But in practice, authorization in medical billing is one of the most time-consuming, administratively burdensome, and financially consequential processes your team deals with every day.

According to a 2023 AMA Prior Authorization Physician Survey, 94% of physicians reported that prior authorization delays patient care. And 79% reported that prior authorization has led to treatment abandonment, patients who simply stop pursuing care after facing authorization barriers. The financial stakes are equally high. Every denied claim due to a missing or invalid authorization is revenue at risk. 

Here you’ll learn how to handle prior authorizations the right way and keep your claims from getting denied.

What Is Authorization in Medical Billing?

Authorization in medical billing, also called prior authorization (PA), pre-authorization, or precertification, is an insurer’s advance approval that a specific medical service meets their coverage criteria and is medically necessary for a specific patient.

Without an approved authorization for a covered service that requires one, the payer will deny the claim, regardless of the clinical appropriateness of the care. The authorization requirement exists to give insurers control over utilization and costs.

From a billing perspective, authorization numbers must be captured before the service, included on the claim, and verified to be within the authorization’s service window and approved service count.

Types of Authorization in Medical Billing

Not all authorizations are the same. Your billing team needs to understand the specific type required for each service:

Prior Authorization (PA)

The most common type. Required before a planned medical procedure, specialty referral, imaging study, or prescription medication is provided. The provider submits clinical criteria, diagnosis, treatment history, and evidence of medical necessity to the payer, who approves or denies the service before care is delivered.

Precertification

Often used interchangeably with prior authorization, precertification typically refers to confirming that a service will be covered at a certain level, particularly for hospital admissions, surgeries, and high-cost procedures. It verifies coverage eligibility and benefit limits, not just medical necessity.

Concurrent Review / Continued Stay Authorization

Used for inpatient care. The insurer reviews the patient’s continued medical necessity for hospitalization at regular intervals, typically every 1–3 days for acute care. If continued stay is not authorized, the payer stops paying for additional days.

Retrospective Authorization

Sometimes called post-service authorization, this applies when care was delivered in an emergency and authorization could not be obtained in advance. The provider submits a retroactive authorization request after the service. Payers have varying policies on whether they accept these, and timelines are typically short.

Referral Authorization

Required under many HMO and gated plan structures. The patient’s primary care physician (PCP) must formally refer them to a specialist, and the plan must authorize that referral before the specialist can see the patient. Seeing the patient without a valid referral authorization results in claim denial.

The Authorization Process: Step by Step

Effective management of authorization in medical billing requires a clear, documented workflow. Every step matters; a breakdown at any point creates AR risk.

Step 1: Identify Whether Authorization Is Required

Not every service requires authorization. Your team must check the patient’s specific insurance plan benefits, not just the payer, because authorization requirements vary by plan tier, product line (HMO vs. PPO), and even employer group. Use your payer portal or clearinghouse eligibility tool to verify authorization requirements at or before scheduling.

Step 2: Gather Clinical Documentation

A successful PA request is built on strong clinical documentation. At minimum, prepare:

• The patient’s current diagnosis with supporting ICD-10 codes
• Documentation of prior treatment history and why previous treatments failed or are contraindicated
• Clinical notes supporting medical necessity, specific, dated, and written in behavioral terms
• The ordering provider’s NPI and contact information
• The proposed CPT code(s) and planned date of service
• Any payer-required clinical criteria forms (often proprietary to each insurer)

Step 3: Submit the Authorization Request

Submit through the payer’s preferred channel. Most large payers now accept electronic PA requests through their provider portal or through an electronic PA platform. Some still require fax; track these by payer to avoid delays.

CMS has been pushing for electronic PA standardization. The CMS Interoperability and Prior Authorization Final Rule (CMS-0057-F), finalized in January 2024, requires payers to implement electronic PA via FHIR-based APIs by January 2027, a significant step toward reducing administrative burden.

Step 4: Document the Authorization

When authorization is approved, document everything precisely:

• Authorization number, required on every claim where the service is billed
• Authorized service dates: the claim must be submitted within this window
• Number of authorized units or visits, do not bill beyond what was authorized without a new request
• Specific CPT codes are authorized; billing a code not listed in the authorization results in denial
• Authorizing clinician’s name (for peer-to-peer review requests, if applicable)

Step 5: Link Authorization to the Claim

When the service is delivered and the claim is submitted, the authorization number must appear in the correct field on the claim form. For professional claims (CMS-1500), this is Box 23. For institutional claims (UB-04), it appears in the appropriate notes field. Missing or misplaced authorization numbers cause automatic claim denial.

Common Authorization Errors That Cause Claim Denials

Authorization in medical billing is detail-sensitive. These are the most common errors that result in preventable denials:

Expired Authorization

Authorization numbers are valid for a specific service window, typically 30, 60, or 90 days from the approval date. Billing a service after the authorization has expired results in automatic denial. Build expiration date tracking into your scheduling system so staff are alerted before each authorized service.

Wrong CPT Code

If the clinical team submits a PA for CPT 93000 (ECG) but the procedure changes to 93010 (ECG interpretation only), the original authorization is invalid for the revised code. Any change in procedure requires a new or amended PA request.

Exceeded Authorized Units

A PA for 12 therapy sessions doesn’t cover a 13th, even if the clinical need is clear. Once authorized units are used, billing additional sessions without a new authorization results in denial. Track visit counts against authorizations in your practice management system and request renewals before the last authorized visit.

Wrong Service Dates on Claim

The dates of service on the claim must fall within the authorized service window. If a scheduled appointment is rescheduled and falls outside the original authorization window, the authorization must be updated before the visit.

Patient Plan Change Not Captured

Authorization is plan-specific. If a patient changes insurance plans or moves from individual to group coverage, any existing PA is void. Verify insurance at every visit, not just at intake.

Authorization Denials and the Appeals Process

When a service is denied due to an authorization issue or when a PA request itself is denied, your team has defined options.

Appealing a PA Denial

When an insurer denies a PA request, they must provide a written denial with the clinical criteria they applied. Your response should:

• Reference the specific clinical criteria the payer cited, and address each point with documentation
• Include peer-reviewed literature or clinical guidelines supporting the proposed treatment
• Request a peer-to-peer review, a direct call between the ordering physician and the payer’s medical reviewer
• File the appeal within the payer’s stated deadline, typically 30–60 days from the denial notice

Retroactive Denial of an Authorized Service

Sometimes a payer authorizes a service but later denies the claim during adjudication, often citing medical necessity or documentation insufficiency. This is a different kind of denial than a PA denial, and your appeal must address the post-service clinical record rather than the original PA criteria.

CMS Rules on Prior Authorization for Medicare and Medicaid

CMS has been actively reforming prior authorization requirements, both to reduce burdens on providers and to protect patient access to care.

Medicare Fee-for-Service (Traditional Medicare)

Traditional Medicare uses prior authorization only for a limited set of services, primarily high-cost, high-utilization items like certain DME, home health episodes, and some imaging studies. The CMS Prior Authorization Model for repetitive scheduled non-emergent ambulance transport (RSNAT) is an example of this targeted approach.

Medicare Advantage (Part C)

Medicare Advantage plans are required to follow traditional Medicare coverage rules, but they are permitted to use prior authorization as a utilization management tool. OIG’s 2022 audit found significant concerns about MA plans using PA inappropriately to deny care that Medicare covers.

The Improving Seniors’ Timely Access to Care Act, passed by the House in 2022 and incorporated into CMS regulations, now requires Medicare Advantage plans to streamline PA processes and increase transparency in their authorization criteria.

Medicaid

Individual states set Medicaid PA requirements within federal guidelines. States must cover federally mandated services without undue barriers, including PA requirements that would create access problems. For behavioral health services specifically, the federal mental health parity law applies to Medicaid managed care plans.

GOLD STANDARD: Building a Prior Authorization Management System

High-performing practices don’t just react to authorization requirements; they build systems that manage them proactively. Here’s what that looks like:

• Service-specific PA requirement checklists are maintained for your top 20 CPT codes and each major payer
• Authorization tracking spreadsheet or software module with expiration alerts and unit counters
• Dedicated PA staff or a designated PA coordinator role, not added to existing billing duties
• Template library for common PA submissions, pre-populated with clinical criteria language that payers accept
• Weekly PA status review meeting, reviewing pending, approved, denied, and expiring authorizations
• Electronic PA submission through clearinghouse or payer portal, wherever available, reducing fax delay and paper errors

For behavioral health and mental health practices specifically, which face some of the highest PA denial rates in outpatient medicine, building a robust authorization management system is not optional. It is a core revenue protection strategy.

Authorization in Medical Billing for Behavioral Health

Mental health and substance use disorder services face a uniquely complex authorization environment. Parity laws require that mental health PA criteria be no more restrictive than those for comparable medical services, but enforcement is inconsistent.

The Mental Health Parity and Addiction Equity Act (MHPAEA), enforced by the Departments of Labor, HHS, and Treasury, prohibits health plans from imposing more restrictive PA criteria on mental health services than on comparable medical/surgical services.

If your behavioral health practice is experiencing significantly higher PA denial rates for mental health CPT codes than for comparable medical services, this may be a parity violation, and you have the right to request a non-quantitative treatment limitation (NQTL) analysis from the insurer.

Get Expert Medical Billing Support 

Billing errors, slow collections, and unresolved denials are costing Tennessee practices thousands every month. Tennessee Billing specializes in complete revenue cycle management for Tennessee healthcare providers, handling every step of the revenue cycle so your clinical team can focus on patients, not paperwork.

Our services include: claim submission and scrubbing, denial management and appeals, AR follow-up, prior authorization support, compliance auditing, and credentialing.

Whether you’re dealing with aging AR, high denial rates, or just need a billing team that actually delivers, we’re here.

Schedule your free billing assessment today, and see what accurate, efficient billing can do for your revenue.

Frequently Asked Questions

How to track expiring prior authorizations daily?

Use practice management software alerts for 7-day warnings on PA expiration dates. This prevents 25% of denials from expired auths, ensuring seamless claim submission. 

What documents win most PA appeals successfully?

Peer-reviewed studies, recent PHQ-9 scores, and failed treatment histories boost appeal success to 80%. Include physician-signed letters addressing payer criteria directly. 

Do all Medicare Advantage plans need PA?

No, only ~15% of MA services require it, but denial rates hit 6%. Always verify via plan-specific portals to avoid unnecessary submission delays. 

What’s the fastest electronic PA submission method?

Clearinghouse portals like Availity or Change Healthcare cut processing to 24-48 hours versus 7-day faxes. Implementation takes 2 weeks for most practices. 

How does MHPAEA help behavioral health PAs?

Parity rules force equal medical/mental health criteria; file NQTL complaints for violations. This reverses 60% of unfair behavioral health denials annually.