In US healthcare billing, a denied claim is money the provider has earned but not yet received. Every denial has a reason, and every reason has a correct next step. Denial management is the skill of reading that reason quickly and taking the right action before deadlines run out.
This is also the topic interviewers love most for AR and billing roles, because it shows whether you truly understand the work. This guide explains the denial process, the codes you will see most often and what to do for each, with interview questions at the end.
Rejection vs denial
A rejection happens before the payer processes the claim, usually for format or data errors, and the claim is corrected and resent. A denial happens after processing: the payer reviewed it and decided not to pay all or part of it. Denials need analysis and the correct action: corrected claim, reprocessing request, records, or a formal appeal.
The denial management process
- Identify: find denied claims from ERAs, payment posting or AR reports.
- Categorise: by reason (eligibility, authorization, coding, timely filing, documentation and so on).
- Analyse: check the claim, payer rules and documentation to find the real cause.
- Act: correct and resubmit, call the payer, send records, or file an appeal.
- Track: follow up until resolved; watch appeal and timely filing deadlines.
- Prevent: report patterns so the front-end, coding or billing team fixes the root cause.
Common denial codes and what to do
| Code | Meaning (simplified) | Typical action |
|---|---|---|
| CO-16 | Claim lacks information or has billing errors | Check the remark code to see what is missing; correct and resubmit |
| CO-18 | Exact duplicate claim or service | Check whether the original claim was paid or is in process; if it was a genuine separate service, correct and explain |
| CO-22 | Care may be covered by another payer (coordination of benefits) | Verify primary and secondary insurance with the patient or payer; bill the correct primary; ask the patient to update COB if needed |
| CO-27 | Expenses incurred after coverage terminated | Verify eligibility on the date of service; find other active insurance or bill the patient as per policy |
| CO-29 | Time limit for filing has expired | Check whether there is proof of timely filing (such as clearinghouse acceptance reports); if yes, appeal with proof; if not, follow the write-off process |
| CO-45 | Charge exceeds the fee schedule or maximum allowable | Usually a contractual adjustment, not a true denial; write off as per contract |
| CO-50 | Not deemed medically necessary by the payer | Review documentation and payer policy; appeal with supporting medical records if justified |
| CO-96 | Non-covered charge | Check plan benefits; bill the patient if allowed and a valid waiver exists, or adjust |
| CO-97 | Service included in payment for another service (bundling) | Review coding edits; if separately payable, correct with the right modifier and resubmit; otherwise adjust |
| CO-109 | Claim not covered by this payer | Find the correct payer and submit there |
| CO-197 | Pre-certification / authorization absent | Check whether authorization was obtained; if yes, send the authorization number; if not, request retro-authorization where the payer allows |
| CO-11 | Diagnosis inconsistent with the procedure | Send to coding for review; correct codes and resubmit |
| CO-4 | Procedure code inconsistent with the modifier, or modifier missing | Correct the modifier with coding team input and resubmit |
| PR-1 / PR-2 / PR-3 | Deductible / coinsurance / copay | Not a denial: transfer to patient responsibility |
Exact descriptions are maintained in the official CARC and RARC code lists and are occasionally updated. Payer-specific rules, such as timely filing and appeal limits, vary, so always follow the client’s payer guidelines.
Appeals: when and how
- When: when you believe the claim was correct and the denial is wrong, such as medical necessity disagreements or timely filing with proof.
- What to include: a clear appeal letter, claim details, the reason the denial should be overturned, and supporting documents (medical records, authorization, proof of timely filing).
- Deadlines: each payer sets its own appeal time limit; missing it usually means the money is lost.
- Levels: many payers have more than one level of appeal, sometimes starting with a reconsideration.
Preventing denials
The best denial is the one that never happens. Most preventable denials come from the front end: wrong patient details, inactive coverage, missing authorizations. Good denial teams track their top denial reasons and share them with the registration, eligibility, authorization and coding teams. This analytical side is what turns an AR caller into a denial analyst.
Interview questions on denials
What will you do if a claim is denied for timely filing (CO-29)?
Check the original submission date and clearinghouse acceptance reports. If the claim was submitted on time, appeal with the proof of timely filing. If it was not, follow the client’s write-off process and flag the cause.
A claim is denied with CO-197. What is your action?
Check whether an authorization was obtained. If yes, provide the authorization number and request reprocessing. If no, check whether the payer allows retro-authorization and work with the authorization team; otherwise follow the client process.
How do you handle a CO-22 denial?
Verify coordination of benefits: confirm which insurance is primary on the date of service, update the patient’s insurance order if needed and bill the correct primary payer.
What is the difference between CO and PR?
CO (contractual obligation) amounts are written off by the provider; PR (patient responsibility) amounts can be billed to the patient.
What information do you note on a payer call about a denial?
Representative’s name, call reference number, date, claim number, denial reason, what is needed to fix it, where to send it, the time limit, and the expected turnaround.
More scenarios: medical billing and AR interview questions and AR caller interview questions.
Frequently Asked Questions
What is denial management in medical billing?
It is the process of identifying denied claims, finding the reason, correcting and resubmitting or appealing them within deadlines, and preventing repeat denials.
What is the CO-16 denial code?
CO-16 means the claim lacks information or has billing errors. Check the accompanying remark code to see what is missing, correct the claim and resubmit.
What does CO-97 mean?
The service is considered included in the payment for another service (bundled). Review coding edits and resubmit with a correct modifier only if the service is separately payable.
What is the difference between a denial and a rejection?
A rejection is returned before processing because of errors; a denial is processed by the payer but not paid, and needs correction or an appeal.
How do you prevent claim denials?
Verify eligibility and authorization before services, code accurately, submit clean claims on time, and analyse denial trends to fix root causes.