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Dental insurance denial codes cheat sheet
What the codes on your EOBs mean in plain English, what usually fixes them, and a follow-up checklist for insurance claims at 0–30, 31–60, 61–90 and 90+ days.
How to read a denial line
Each adjusted line on an EOB or electronic remittance (ERA) carries up to three codes:
- A group code (CO, PR, OA or PI): who is responsible for the amount.
- A CARC, Claim Adjustment Reason Code: why the payer adjusted or denied the line. Written together with the group, for example CO-16.
- A RARC, Remittance Advice Remark Code (optional): the extra detail, for example N37, missing tooth number.
So CO-16 + N37 reads: “contractual adjustment, the claim is missing information, specifically the tooth number.” The fix is a corrected claim, not an appeal.
Group codes
| Group | Meaning | What it means for you |
|---|---|---|
| CO | Contractual obligation | You can’t bill the patient for this amount unless the problem is fixed. Either fix and resubmit, appeal, or write it off. |
| PR | Patient responsibility | The patient owes this amount (deductible, coinsurance, co-pay, annual maximum and so on). Move it to the patient balance and send a statement. |
| OA | Other adjustment | Neither of the above, often used for duplicates and coordination of benefits. Read the CARC to know what to do. |
| PI | Payer-initiated reduction | The payer reduced the payment on its own terms. Treat like CO: don’t bill the patient without checking. |
CARC codes: meaning, fix and next action
The group shown is the one you’ll usually see with each code. Always read the group on your own EOB: the same number with a different group can mean a different action.
| Code | What the payer is saying | Likely fix | Next action |
|---|---|---|---|
| PR-1, PR-2, PR-3 | Deductible, coinsurance or co-pay. This is the patient’s share under their plan. It isn’t a denial. | Move the amount to the patient balance and send a statement. | Bill patient |
| CO-4, CO-11 | Coding mismatch: the code doesn’t match the rest of the claim (modifier, diagnosis or area). | Check the code, tooth and area against the clinical note and send a corrected claim. | Send corrected claim |
| CO-16 + N37 | Missing tooth number: the claim had no valid tooth number for this procedure, so the payer couldn’t process it. | Take the tooth number from the clinical note and send a corrected claim. No appeal needed. | Send corrected claim |
| CO-16 + N56 | Wrong procedure code: the code billed doesn’t match the service documented. | Check the note against the code and send a corrected claim. Common case: D4341 billed when charting shows only 1–3 teeth with deep pockets in the quadrant, which is D4342. | Send corrected claim |
| CO-16 (other) | The claim lacks information or has a billing error. For dental this is usually a missing X-ray or narrative. | Read the RARC, then send the missing documentation (see “What payers usually want” below). | Send documentation |
| CO-18 or OA-18 | Duplicate: the payer thinks this is a copy of a claim it already has. | Check the original claim. If it’s processing or paid, close this one. If the original was denied, call to have it reprocessed. | Check original claim |
| CO-22 or OA-22 | Coordination of benefits: the payer thinks another plan is primary and wants that plan’s EOB first. | Ask the patient to update their other-coverage details with the payer (usually a short call), or bill the primary plan first and send its EOB. | Update COB, resubmit |
| OA-23 | The payment reflects what a prior payer already paid or adjusted. Usually seen on secondary claims. | Compare with the primary EOB. Usually nothing to fix; if the math looks wrong, call the payer. | Check against primary EOB |
| CO-27 | Coverage ended: the patient’s coverage had ended before the date of service. | Re-check eligibility for the date of service and ask the patient for any new insurance. Bill the new plan, or move the balance to the patient. | Verify eligibility, ask patient |
| CO-29 | Timely filing: the claim arrived after the payer’s filing deadline. | Find proof of timely filing, such as the clearinghouse acceptance report with the original submission date, and appeal with it. With no proof, it’s a write-off. | Appeal with proof of filing |
| CO-45 | Charge is above the fee schedule or contracted fee. A routine contractual write-down, not a denial. | Post the write-off. Check the allowed amount matches your contracted fee schedule. Don’t bill the patient the difference if you’re in network. | Adjust, spot-check fees |
| CO-50 | Not medically necessary: the payer doesn’t think the treatment was needed, based on what it received. | Appeal with X-rays, charting and a narrative showing why it was needed. | Appeal with records |
| CO-96, CO-204 | Not covered by the plan. For bridges and implants (D6xxx) this is often a missing-tooth clause: the tooth was lost before coverage started. | Implants and bridges: if the tooth was extracted while the patient was covered, appeal with the extraction date and records. Otherwise, confirm with the payer and bill the patient if they signed a financial waiver. | Check extraction date, or confirm and bill patient |
| CO-97 | Bundled: the payer says this was included in another service paid the same day. Common with a core buildup (D2950) placed with a crown. | D2950: if the buildup was needed to hold the crown, appeal with the pre-op X-ray and a narrative; if not, write it off and don’t bill the patient. Palliative treatment (D9110) with definitive treatment the same day: write off unless it was a separate visit. | Review note, appeal or write off |
| CO-109 | Wrong payer: this payer says it isn’t responsible for this patient or service. | Re-check the insurance card and eligibility, then send the claim to the right payer. | Find correct payer |
| PR-119 | Annual maximum reached: the patient has used this year’s plan maximum. | Confirm remaining benefits with the payer. If correct, move the amount to the patient balance. If the benefit year resets soon, note it for future treatment. | Confirm max, then bill patient |
| CO-119, CO-151 | Frequency limit: the service was done more often than the plan allows, for example a third cleaning in a year, or a full set of X-rays within 5 years. | Check the patient’s history with the payer. If the earlier service was at another office, was a different code, or is outside the window, appeal with the dates. If the limit really was reached, bill the patient only if they signed a financial waiver. | Verify history with payer |
| CO-197 | No pre-authorization: the plan required a predetermination or pre-authorization that wasn’t on file. | Check whether a predetermination was sent. If yes, send its reference number. If not, request a retro review with the documentation. | Request retro review |
| CO-252 | Attachment required: the payer needs an X-ray, charting or narrative before it will pay. | Send the documentation listed below. For scaling and root planing (D4341/D4342), that’s perio charting. | Send documentation |
Patient responsibility always comes from the group code, not the reason. PR means you can bill the patient. CO means you can’t, unless the problem is fixed, the plan really doesn’t cover it and the patient signed a financial waiver before treatment.
What payers usually want, by procedure
For CO-16, CO-50, CO-97, CO-197 and CO-252, the fix is usually documentation. This is what to send.
| Procedure | Codes | Send |
|---|---|---|
| Crowns, onlays, buildups | D27xx, D2950–D2999 | Pre-op X-ray of the tooth and a short narrative: fracture, decay or failing restoration, and the % of tooth structure lost. |
| Scaling and root planing | D4341, D4342, D435x | Full-mouth perio charting (pocket depths, dated within 12 months) and X-rays showing bone loss. |
| Bridges and implants | D60xx–D62xx, D65xx, D67xx | X-ray, the extraction date of the missing tooth, and a narrative. |
| Endodontics | D3xxx | Pre-op periapical X-ray and a diagnosis narrative. |
| Oral surgery | D7xxx | Pre-op X-ray and the operative note. |
| Other restorative | D2xxx | Pre-op X-ray or intraoral photo and the clinical note. |
| Anything else | The clinical note for that date of service. |
RARC remark codes
| Code | What it means | What to do |
|---|---|---|
| N4 | Missing, incomplete or invalid prior insurance carrier EOB. | Send the primary plan’s EOB with the secondary claim. |
| N20 | Service not payable with another service on the same date. | Bundling. If it was a separate, distinct service, appeal with the note. Otherwise write off per contract. |
| N30 | Patient ineligible for this service. | Check eligibility and plan limits for the date of service. Ask the patient about other coverage. |
| N37 | Missing or invalid tooth number or letter. | Send a corrected claim with the tooth number from the clinical note. |
| N56 | Procedure code not correct or valid for the service or date billed. | Check the note against the code and send a corrected claim. |
| N130 | Consult plan benefit documents for restrictions on this service. | A plan limitation applies. Check the benefits breakdown or call the payer to find out which one. |
| N362 | Days or units of service exceed the payer’s maximum. | Check the units billed. Correct the claim if wrong; otherwise treat as a frequency limit. |
| N381 | Consult the contractual agreement for restrictions or payment terms. | Check your contract and fee schedule with this payer. |
| N705 | Incomplete or invalid documentation. | Resend complete, legible documentation, dated and labeled with the tooth or area. |
| N706 | Missing documentation. | Send the documentation for the procedure (table above). |
| M127 | Missing patient record for this service. | Send the clinical note for the date of service. |
| M80 | Not covered when performed in the same session or date as a service already processed. | Bundling. Appeal only if it was clearly separate; otherwise write off per contract. |
| MA04 | Secondary payment can’t be considered without the primary payer’s details. | Send the primary EOB with the secondary claim. |
Insurance AR follow-up checklist
Days are counted from the date the claim was sent. Work the oldest money first, but never let a 0–30 claim slide into 31–60 for want of a two-minute fix.
0–30 days
- Check the clearinghouse rejection report at least weekly. A rejection never reached the payer, so it won’t show as a denial.
- Fix and resend rejected claims within two business days.
- Confirm attachments went out for claims that need them: crowns, scaling and root planing, bridges, implants.
- No EOB after 14–21 days? Check the claim status on the payer portal.
- Post EOBs and ERAs as they arrive. Move patient portions (PR) to the patient balance and send statements.
31–60 days
- Check the status of every unpaid claim. Note the date, the reference number and who you spoke to.
- Work every denial by its code: corrected claim, documentation, appeal or patient balance.
- Resend missing attachments and ask the payer to confirm they were received.
- Ask patients with coordination of benefits denials (CO-22) to update their other coverage with the payer.
- Write each payer’s timely filing and appeal deadlines next to its open claims.
61–90 days
- Call the payer on every open claim and get a specific answer and an expected payment date.
- File appeals with a short cover letter, the documentation and a copy of the claim. Note the appeal deadline.
- Escalate stuck claims to a supervisor or your provider relations representative.
- Tell patients whose balance depends on the outcome what’s happening and when you expect an answer.
90+ days
- Check timely filing and appeal deadlines first. Some 90+ claims can still be saved this week and not next month.
- For each claim, decide: second-level appeal, bill the patient (only if it’s PR, or a waiver was signed), or write off per contract. Write down the reason.
- For a valid claim a fully insured plan won’t process, a complaint to your state insurance department is a last resort.
- Look for patterns. The same code from the same payer, again and again, means a fix at the front desk: eligibility checks, tooth numbers or attachments.
Every week
- Run the insurance aging report by payer and write down the total in each bucket.
- Pick the five oldest claims with the most money and work them first.
- Note your three most common denial codes this month. Each one is a process fix waiting to happen.
Code meanings are from the standard CARC and RARC code lists used on EOBs and electronic remittances, shortened into plain English. Payers apply codes differently and plans differ: always read the full EOB and check the payer’s rules and your contract. This sheet is general guidance, not legal or compliance advice.
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