Prior authorization denials happen for a handful of predictable reasons, and most of them are fixable. Your insurer may have decided the treatment isn’t medically necessary, your paperwork may have been incomplete, or your plan may require you to try a cheaper option first. The good news: many denials are overturned on appeal, often simply because additional documentation gets submitted the second time around.
The Most Common Reasons for Denial
Your denial letter should include a reason code or explanation, but these are often vague. Here’s what they typically translate to in practice.
Insufficient documentation. This is the single most common trigger. Your doctor’s office submitted the request, but the insurer decided the clinical notes, test results, or justification weren’t detailed enough to prove you need the treatment. It doesn’t necessarily mean you don’t qualify. It means the paperwork didn’t make the case clearly enough.
Medical necessity not established. The insurer’s reviewer looked at your records and concluded the requested treatment, test, or medication isn’t warranted for your specific diagnosis. This can happen when clinical guidelines suggest a different approach, when your condition hasn’t progressed to a threshold the insurer requires, or when lab results or imaging don’t support the request.
Step therapy (“fail first”) requirements. Your plan may require you to try a less expensive treatment before it will cover the one your doctor prescribed. These policies are built into the prior authorization process, and they’re especially common with specialty medications and biologics. If you haven’t documented failure on the first-line drug, the insurer will deny the more costly one. Patients who previously tried and failed the cheaper option should be exempt from step therapy, but you’ll need records proving it.
Incorrect coding or administrative errors. A wrong diagnosis code, a mismatched procedure code, or a missing reference number can trigger an automatic denial before a human even reviews your case. These are among the easiest denials to fix.
Out-of-network or plan exclusion issues. Sometimes the denial has nothing to do with your medical situation. The provider, facility, or specific service may not be covered under your plan, or the treatment may fall outside your plan’s formulary or benefit structure entirely.
Why Specialty Medications Get Extra Scrutiny
If your denial involves a high-cost drug, particularly in areas like oncology, autoimmune disease, or rare conditions, insurers apply additional clinical criteria. In one study of chemotherapy prior authorization requests, about a third of denials were due to lack of support in recognized drug references, a quarter were based on clinical criteria the patient didn’t meet, and roughly 23% involved issues with dosing or frequency. Another 11% were denied because clinical test results didn’t support the drug’s use.
Cost is explicitly part of the calculation. When an equally effective, lower-cost alternative exists, insurers will often deny the more expensive option unless your doctor demonstrates why the alternative won’t work for you specifically.
What to Do Immediately After a Denial
You have a limited window to act, so don’t wait. Start with these steps:
- Call your insurer and get the specific reason. The denial letter may be generic. A phone call can reveal the exact clinical criterion you didn’t meet, the missing document, or the coding error that caused the rejection.
- Contact your doctor’s office with that reason. Share exactly what the insurer told you. Your physician’s staff may be able to supply additional records, correct a coding mistake, or write a stronger justification.
- Note your deadlines. Your denial letter will include a timeframe for filing an appeal. Missing it can forfeit your right to challenge the decision.
- Request your full claim file. Under federal law, you have the right to review every document the insurer used to make its decision, including the clinical guidelines or criteria they applied.
How the Appeal Process Works
Federal law under the Affordable Care Act gives you the right to appeal any denial from a health plan created after March 2010. The process has two distinct stages.
Internal Appeal
This is your first step. You submit a written appeal to your insurance company that includes your prior authorization reference number, your diagnosis, the procedure or treatment codes, and a clear explanation of why the treatment is necessary. Describe how the denial affects your quality of life, what your care team recommends, and why the requested service matters for your health. For individual health insurance plans, the insurer must complete at least one level of internal review before issuing a final decision.
The insurer is required to have the appeal reviewed by someone who wasn’t involved in the original denial, and that person must be impartial. Follow up frequently to check on the status and ask whether any additional information is needed.
External Review
If the internal appeal fails, you can escalate to an external review. This sends your case to an independent review organization (IRO) that has no financial relationship with your insurer. The IRO is assigned randomly or through a rotation system to prevent bias. For standard reviews, the IRO must issue a written decision within 45 days. The IRO’s decision is binding on the insurer.
External reviews are available for any denial based on medical necessity, appropriateness, level of care, or clinical effectiveness. This is a powerful tool, and many patients don’t realize it exists.
The Peer-to-Peer Review Option
Before or during the formal appeal, your doctor can request a peer-to-peer review. This is a phone call where your treating physician directly discusses your case with a doctor employed by the insurer. The goal is to explain why the treatment is necessary and, ideally, get the denial reversed on the spot.
These calls can be effective, but there’s a well-documented problem: the insurer’s reviewer often doesn’t practice in the same specialty as your doctor. The American Medical Association has pushed for reforms requiring that the reviewer have clinical expertise in the condition being treated. If your doctor feels the reviewer lacked relevant knowledge, that’s worth noting in a subsequent written appeal.
What Makes a Strong Letter of Medical Necessity
A letter of medical necessity from your doctor is often the single most important document in overturning a denial. A strong letter includes several specific elements: a clear description of what’s being prescribed, a medical explanation demonstrating why you need it, and a rationale linking the treatment directly to your diagnosed condition. If the insurer wants you to try a cheaper option first, the letter should explain why common alternatives are insufficient or unavailable for your situation, and why the requested treatment will improve your condition within a reasonable timeframe.
For therapies, the letter should specify the quantity, frequency, and duration of treatment and describe how it will lead to measurable improvement. For equipment or devices, it should explain how long the item is needed and reference a recent physical exam. Vague language like “patient would benefit” isn’t enough. Specificity is what wins appeals.
Appeals Succeed More Often Than You’d Think
Many people assume a denial is final. It isn’t. CMS data from fiscal year 2024 shows that first-level appeals overturn denials at meaningful rates across multiple categories: 51.6% for home health services, 45.1% for non-emergency ambulance transport, and 38.4% for durable medical equipment like wheelchairs and oxygen supplies. Hospital outpatient services had an 18.4% overturn rate.
The most common reason appeals succeed is straightforward: additional documentation was submitted that wasn’t included in the original request. That means many initial denials aren’t really about whether you qualify. They’re about whether the right paperwork made it to the right reviewer. A denial is the start of a conversation, not the end of one.