How to Appeal a Denied Medical Billing Claim

I see you just opened a denial letter. I know that feeling. Your stomach drops, and you start wondering what went wrong. Take a breath. You are not the first to get one, and you won’t be that last. Denials happen all the time in U.S. billing, it’s not a judgment against you.

Here’s what I would say to someone on my team right then: focus on the facts first, gather the right documents, and follow a few clear steps to get the claim back on track. In the next section I will walk you through those immediate actions, what to check first, what to document, and when to escalate, so you can resolve the denial and restore cash flow.

Open the denial and find two things, nothing else matters yet

Ignore everything on that EOB or ERA except the CARC code and the RARC code. That’s it for now.

CARC tells you why it was denied

RARC gives you the extra detail

You’ll see the same handful over and over once you’ve been at this a while:

• CO-16 = they need more information, something’s missing
• CO-50 = not medically necessary in their eyes
• CO-97 = bundled into another service already paid
• CO-29 = you missed the filing window
• PR-1 = it’s going to the deductible, not really a denial at all, patient owes this

Before you do anything else, find the deadline and write it down

This is the step people skip because they’re excited to start writing the appeal. Don’t. First, figure out how much time you actually have.

Medicaid depends on the state, and some states only give you 60 days

Put this date somewhere you’ll actually see it, your tracking sheet, your PM system, wherever you check daily. This is the one mistake in this job you cannot undo. Once that window shuts, that money is gone.

Now go read the actual chart, not just the claim

Before you write one word of an appeal, pull the note. You’re checking:

• Does the documentation actually support the CPT code that got billed
• Is medical necessity spelled out clearly in the note itself, not just implied
• Any missing signature, missing date, or incomplete section the payer could hang another denial on
• Does the diagnosis code on the claim actually match what the provider wrote

Different denial, different fight, here’s how to handle each one

Not all denials are created equal, and treating them like they are is how appeals get rejected twice. A CO-50 needs clinical proof. A CO-97 might not need an appeal at all, just a corrected claim. A timely filing denial comes down to one piece of paper you either have or don’t. Know which fight you’re in before you write a single word of the appeal.

#1. Medical necessity (CO-50)

Get the provider to write a short clinical explanation of why the service was needed for this specific patient. Then go find the payer’s actual published medical policy for that CPT code. Line up the documentation against their own criteria, point by point. You’re not arguing your opinion, you’re showing them their own rule is satisfied.

#2. Bundling denials (CO-97)

Check NCCI edits if it’s Medicare, or the payer’s bundling policy if it’s commercial. Half the time this is just a missing modifier, 59 or XU usually, and the real fix is a corrected claim, not a formal appeal at all. Only appeal if you can show the two services were genuinely separate and distinct.

#3. Timely filing (CO-29)

This one lives or dies on proof. You need your clearinghouse acceptance report, the EDI report, or a certified mail receipt showing the original claim went out on time. No proof, no case. This is exactly why you save clearinghouse reports for a full year minimum, because you will need one eventually and you won’t know which one until you do.

#4. Authorization or eligibility denials

First check if auth was actually required for that CPT and date of service, sometimes staff assume it was needed when it wasn’t, or the other way around. If auth was obtained, put the auth number and approval date right in the appeal letter, don’t make them dig for it.

The letter itself, keep it boring and factual

Reviewers go through hundreds of these. Don’t write a story. Give them what they need to say yes, fast.

Here’s a structure that has worked for my team for years:

• Patient name, date of birth, member ID, and claim number at the top, always
• One sentence stating clearly what you are appealing and why
• A short paragraph of clinical or factual justification
• Reference to the specific payer policy, CMS guideline, or state Medicaid rule that supports your position
• Attach the supporting documents: chart notes, authorization, itemized bill, proof of timely filing, whatever applies
• A clear closing statement asking for reconsideration and payment

In case you need a template that you can literally hand to your team and have them fill in brackets, then below is the one:

Same skeleton every time. Only the middle paragraph and the denial reason change depending on whether it’s necessity, bundling, timely filing, or auth.

Know how far this can actually go before you invest more time in it

Medicare: Redetermination, then reconsideration by a QIC, then an ALJ hearing, then the Medicare Appeals Council, then federal court if it ever gets that far. Most claims never leave the first two steps.

Commercial: Typically two internal appeal levels, then external review through your state’s insurance department if it’s a fully insured plan. Payers won’t bring this up on their own, but the right exists in most states.

Medicaid: Different in every state. Don’t assume it works like Medicare, pull up your specific state’s provider manual.

Submitting the appeal is not the end, this is where money gets lost

Most practices do everything right up to hitting send, then just wait. Don’t be that practice.

Log it, date sent, payer, claim number, appeal level, outcome, even a plain spreadsheet works

Nobody at the payer is losing sleep over your unpaid claim. If you don’t follow up, it just sits there.

Not every denial deserves a fight

If it’s a small dollar amount and the documentation genuinely doesn’t back it up, write it off and move on. Fix whatever caused it so it stops happening, but don’t burn hours chasing a claim that was never going to get paid. Pick your battles based on dollar amount and odds, not principle.

The real win is stopping the denial before it starts

Once you’ve worked enough of these, you’ll start seeing the same codes from the same payers for the same reasons. That’s your signal to fix the front end instead of fighting the back end forever.

• Verify eligibility and benefits before every visit, every patient, not just new ones
• Confirm whether auth is needed before the service happens, not after
• Build a simple checklist that catches missing modifiers and mismatched diagnosis codes before the claim goes out
• Make sure front desk is getting accurate insurance IDs and demographics at check in

Every denial you stop at the front door is one your team never has to appeal. If denials are still slipping through despite these fixes, a structured denial management solution can help you track root causes and close the gaps for good. 

FAQs

1. How long does the payer have to respond to an appeal?

Medicare usually answers redeterminations within 60 days. Commercial payers vary, often 30 to 60 days, but check the specific provider manual since there’s no single rule across the industry.

2. Can the patient file the appeal instead of the practice?

Yes, and sometimes their appeal carries more weight, especially for external review. Worth pulling them in in when it’s a treatment they clearly need.

3. Appeal got denied again, now what?

Move to the next level if the dollar amount and odds justify the time. Once internal levels are used up, check if external review applies for that plan in your state.

4. Is a corrected claim the same as an appeal?

No. Corrected claims are for fixable errors, wrong modifiers, typo, that kind of thing. Formal appeal is for payer decisions like necessity or timely filing. Sending a correction when you needed an appeal just burns your deadline for nothing.

5. Can you keep appealing the same claim forever?

No, each payer and each level has a set number of shots. Once you’ve used them all, it’s final unless external review or, for Medicare, an ALJ hearing is still on the table.