Prior authorization is one of the most common reasons a legitimate, well-coded claim still gets denied. When a payer requires approval before a service and that approval is missing or incomplete, the claim stalls no matter how clean the coding is. This guide is a practical reference for practices that want to get authorizations right the first time and keep them from becoming a bottleneck.
Use it as a quick cheat sheet covering what prior authorization is, which services usually need it, a step-by-step workflow, and the payer-specific habits that prevent avoidable denials.
What Is Prior Authorization?
Prior authorization, sometimes called pre-authorization or pre-certification, is a payer's requirement that a provider obtain approval before delivering a specific service, procedure, or medication. The payer reviews medical necessity against its coverage criteria and issues an authorization number if approved. Without that approval on file, the service is typically not reimbursed, even when it was clinically appropriate.
Why Prior Authorization Matters in Medical Billing
Handling authorizations well protects both revenue and the patient experience. Done consistently, it delivers:
- Fewer denials for services that required approval
- Faster, more predictable reimbursement
- Accurate patient cost expectations before care
- Less staff time spent on appeals and rework
- Better compliance with payer medical-necessity rules
Most Common Services Requiring Prior Authorization
Requirements vary by payer and plan, but certain categories are frequently gated behind approval.
| Service Category | Common Examples |
|---|---|
| Advanced imaging | MRI, CT, PET scans |
| Surgical procedures | Elective and outpatient surgeries |
| Durable medical equipment | Wheelchairs, CPAP, orthotics |
| Specialty medications | Infusions and biologics |
| Inpatient admissions | Non-emergency hospital stays |
| Behavioral health | Inpatient and intensive outpatient programs |
| Physical and occupational therapy | Extended or ongoing therapy plans |
| Genetic and specialized testing | Molecular and genetic panels |
Prior Authorization Workflow Checklist
A repeatable workflow keeps authorizations from slipping through the cracks:
- 1Identify at scheduling whether the service requires authorization.
- 2Confirm the requirement against the patient's specific plan.
- 3Gather clinical documentation supporting medical necessity.
- 4Submit the request through the payer portal, fax, or phone.
- 5Record the reference or authorization number and effective dates.
- 6Track pending requests and follow up before the visit.
- 7Confirm approval covers the exact CPT codes and units planned.
- 8Attach the authorization number to the claim at submission.
Common Prior Authorization Denial Reasons
- No authorization obtained before the service
- Authorization expired before the date of service
- Approved service or CPT code does not match what was billed
- Insufficient documentation of medical necessity
- Request submitted to the wrong plan or payer
- Units or visit count exceeded the approved amount
Top CPT Codes Frequently Requiring Prior Authorization
The codes below are common examples of services that payers often review. Always confirm against the specific plan, since requirements change.
| CPT Code | Description |
|---|---|
| 70553 | MRI brain, with and without contrast |
| 72148 | MRI lumbar spine, without contrast |
| 74177 | CT abdomen and pelvis, with contrast |
| 78815 | PET/CT skull base to mid-thigh |
| 27447 | Total knee arthroplasty |
| 43239 | Upper GI endoscopy with biopsy |
| 95810 | Polysomnography, sleep study |
| 97110 | Therapeutic exercise, per 15 minutes |
| 64483 | Injection, transforaminal epidural, lumbar |
| J1745 | Infliximab infusion, per 10 mg |
ICD-10 Examples Commonly Reviewed During Authorization
Diagnosis codes support the medical necessity behind a request. Common examples reviewed during authorization include:
- M54.5, low back pain
- G47.33, obstructive sleep apnea
- M17.11, unilateral primary osteoarthritis of the knee
- R51.9, headache
- K21.9, gastroesophageal reflux disease
- M25.561, pain in right knee
Payer-Specific Prior Authorization Tips
- Medicare Advantage: These plans set their own authorization lists that differ from traditional Medicare, so confirm requirements per plan rather than assuming Medicare rules apply.
- Large commercial payers: Many route advanced imaging and certain procedures through third-party benefit managers, so submit to the correct review vendor, not just the health plan.
- Blue Cross Blue Shield: Requirements can vary by state plan and product, so verify against the member's specific card and plan rather than a national standard.
Best Practices to Reduce Authorization Denials
- Verify authorization requirements during eligibility, not after the visit
- Build documentation habits that capture medical necessity up front
- Track expiration dates and requested units for every approval
- Reconcile the approved codes against what is actually billed
- Keep a payer-specific reference of what needs authorization
When to Get Help
Prior authorization is time-consuming, and the rules shift constantly across payers and plans. Practices with high imaging, surgical, therapy, or specialty-drug volume often find the administrative load pulls staff away from patient care. At ClaimSphere RCM, our certified team manages authorizations end to end, confirming requirements, submitting clean requests, tracking approvals, and matching them to billed claims so services are covered before they happen. If missing or mismatched authorizations are costing you revenue, we can take that burden off your front office and keep your reimbursements on track.
