Dental claim adjustment codes: CO-45, CO-97, PR-1 and the rest, explained
What the group and reason codes on a dental EOB or ERA mean, who owes the money for each, the fifteen codes a dental office sees most, and what the front office does next.
By Dr. Salem Sayegh, general dentist, Glendora, California ·
The short answer: every adjustment on a dental EOB or ERA is a two-letter group code plus a reason number. The letters say who owes the money: CO means the office absorbs it under its contract, PR means the patient owes it. The number says why. CO-45 is the normal in-network write-off, CO-97 means the procedure was bundled into another one, and PR-1, PR-2 and PR-3 are the patient’s deductible, coinsurance and copay.
Most of what is written about these codes is for medical billing, and some of the advice does not carry over. In dentistry the codes arrive alongside CDT procedure codes, payer frequency rules and alternate-benefit clauses that medical billers rarely see. This guide is the reference I wish my front office had on day one. It covers the codes we actually see in my practice in Glendora, and what we do with each.
How to read an adjustment code
Take CO-45. The group code CO tells you the adjustment is a contractual obligation. The reason code 45 tells you the charge was above the payer’s fee schedule. Together they say: your fee was higher than your contracted fee, and you agreed in your contract to write off the difference. The same reason number can appear under a different group. A PR-96 is a non-covered service the patient pays for. A CO-96 would mean the office absorbs it, which is worth questioning.
| Group | Meaning | What it tells the office |
|---|---|---|
| CO | Contractual obligation | The office absorbs it under its contract. Do not bill the patient. |
| PR | Patient responsibility | The patient owes it. Move it to the patient balance. |
| OA | Other adjustment | Neither of the above, often coordination of benefits. Read the reason code. |
| PI | Payer-initiated reduction | The payer reduced it without a contractual basis. Worth a second look. |
A third layer sometimes follows: a remittance advice remark code (RARC), which adds detail such as which attachment was missing. A CO-16 or CO-252 without its remark code tells you something is missing but not what, so always read the remark too.
The adjustment codes a dental office sees most
The X12 list runs to hundreds of codes, but a general dental practice sees the same fifteen or so again and again. Descriptions below are paraphrased from the official list.
| Code | Meaning | Where you see it in dentistry | What to do |
|---|---|---|---|
| 1 | Deductible | First claims of a benefit year | PR: bill the patient |
| 2 | Coinsurance | The patient’s percentage on basic or major services | PR: bill the patient |
| 3 | Copayment | Fixed-copay (DHMO-style) plans | PR: bill the patient |
| 16 | Claim lacks information or has a billing error | Missing tooth number, surface, quadrant or attachment | Correct and resubmit; read the remark code for what is missing |
| 18 | Exact duplicate claim or service | Claim sent twice, or sent electronically and on paper | Usually nothing to do; check the first claim was paid |
| 22 | May be covered by another payer (coordination of benefits) | Patient has two plans and the order is wrong or unknown | Confirm primary and secondary, then rebill |
| 27 | Expenses incurred after coverage terminated | Patient changed jobs or plans | Verify current coverage; bill the new plan or the patient |
| 29 | Time limit for filing has expired | Claim sent after the payer’s filing deadline | Appeal only with proof of timely filing; otherwise the office absorbs it |
| 45 | Charge exceeds the fee schedule or maximum allowable | Every in-network claim where your fee is above the contracted fee | CO: write off the difference |
| 96 | Non-covered charge | Procedure excluded by the plan, such as some cosmetic work | Usually PR: bill the patient if they were told in advance |
| 97 | Benefit included in the payment for another service | Pulp cap or desensitizer with a filling, buildup with a crown | CO: write off, or appeal with documentation |
| 119 | Benefit maximum for this time period or occurrence reached | Annual maximum used up; some payers use it for frequency limits | Check the benefit history; usually PR |
| 151 | Information submitted does not support this many services or this frequency | Third prophy in a year, bitewings too soon, FMX inside five years | Check the history; appeal if the payer has it wrong |
| 197 | Precertification or pre-treatment authorization absent | Plans that require predetermination for crowns or implants | Request authorization and appeal, if the plan allows it after the fact |
| 204 | Not covered under the patient’s current benefit plan | Implants or orthodontics on a plan without that coverage | Usually PR: bill the patient |
| 252 | An attachment or other documentation is required | Crown, SRP or buildup sent without radiographs, perio charting or a narrative | Send the attachment; this is the most fixable denial there is |
Each linked code has its own page with the dental causes, what to do and whether the patient owes it. The full list, including remark codes like N130, is at dental denial codes.
What does CO-45 mean, and should you worry about it?
No. CO-45 is the most common adjustment on any in-network dental claim. If your office fee for a crown is $1,400 and your contracted fee with the plan is $950, the EOB shows a $450 CO-45 adjustment. You write that off, and you cannot bill it to the patient. That is the deal you made when you joined the network.
What deserves attention is the size of the CO-45. If the allowed amount is lower than the fee in your contract, the payer has used the wrong fee schedule or an outdated one. The EOB will still say CO-45, and nothing on it will look like a denial. That is an underpayment, and the only way to catch it is to compare each allowed amount with your contract. EOB scrubbing covers how to do that.
What does CO-97 mean on a dental claim?
CO-97 means the payer has decided the procedure is part of another procedure it already paid for, so it pays nothing extra. Search results for CO-97 are dominated by medical billing advice about NCCI edits and modifier 59. Most dental claims do not use modifiers that way, so that advice rarely helps. In a dental office, CO-97 usually comes from one of these pairings:
- Core buildup (D2950) with a crown. Many plans pay a buildup only when it is needed to retain the crown, not as a routine part of the preparation.
- Pulp cap (D3110 or D3120) with a restoration on the same tooth and date.
- Desensitizing medicament or resin with a restoration on the same tooth.
- Palliative treatment (D9110) with definitive treatment on the same visit.
- Individual periapical images with a full-mouth series taken close together.
The fix is clinical documentation, not coding tricks. If a buildup was needed because most of the coronal tooth structure was gone, say so in a narrative and send the pre-operative radiograph or an intraoral photo. If the plan bundles the pair as a matter of policy, the appeal will fail. Under most in-network contracts the bundled amount is then written off rather than billed to the patient. Check what your contract says about disallowed procedures.
PR-1, PR-2 and PR-3: the patient’s share
These three move money to the patient. PR-1 is the deductible, PR-2 is coinsurance (the patient’s 20% or 50%), and PR-3 is a fixed copay. They should add up, together with the plan payment, to the allowed amount. If they do not, something on the EOB needs a second look before you post it. How to read a dental EOB works through that arithmetic on a real line.
The four denials we see most, and the codes behind them
In my office, four problems account for most of the reduced or denied lines. Each one shows up under different codes depending on the payer, which is part of what makes them easy to miss.
- Downgrades. A posterior composite paid at the amalgam rate, because the plan has an alternate benefit (least expensive alternative treatment) clause. Payers report these in different ways: as a reduced allowed amount under code 45, or with their own remark code explaining the alternate benefit. Under many PPO contracts the patient owes the difference up to your contracted fee for the composite, but check your contract and your state’s rules before billing it.
- Frequency limits. A prophy, bitewings, a full-mouth series or fluoride denied as too soon, usually under 119 or 151. Plans count frequency differently: per calendar year, per benefit year, or per rolling twelve months. Before you accept the denial, check the patient’s history. Payers sometimes count a visit from another office or the wrong date.
- Missing documentation. Crowns, scaling and root planing, buildups and some extractions pended or denied for missing radiographs, perio charting or a narrative. This comes through as CO-16 or CO-252 with a remark code naming what is missing. It is the most recoverable denial there is: send the attachment.
- Underpayment against the fee schedule. The allowed amount is lower than your contracted fee, or the plan applied the wrong network’s fee schedule. The EOB just says CO-45. Nothing flags it unless someone compares the numbers.
Paper EOB remark codes are not the same as CARCs
The codes above come from the national X12 list used in the electronic remittance advice, the 835 file. Many dental payers print their own remark codes on paper and portal EOBs instead: a letter, or a short number with a legend at the bottom of the statement. One payer’s code 45 may not match another’s, and neither has to match the CARC. If your office posts from portal EOBs, keep each major payer’s legend handy, or use software that reads the legend for you. ERA vs. EOB vs. EFT explains the difference between the two formats.
Where an AI agent fits
Reading a code is easy. Reading every code on every line of every EOB, every day, without missing the one CO-45 that is $80 short, is the hard part. Sai for Dentists reads each line as it posts, checks the allowed amount against your fee schedule, and puts denials, downgrades and underpayments on a list for your team to act on. It does not decide whether to appeal. A person decides that, with the reason already in front of them.
Sources
- X12 claim adjustment reason codes, claim adjustment group codes and remittance advice remark codes.
- American Dental Association, CDT: Code on Dental Procedures and Nomenclature.
- 45 CFR 162.1602, the HIPAA standard for electronic remittance advice (the 835).
Common questions
What does CO-97 mean on a dental claim?
CO-97 means the payer considers the procedure included in the payment for another procedure it has already processed, so it pays nothing separately for it. In dentistry it usually shows up on a pulp cap, desensitizing treatment or palliative visit billed on the same day as a restoration, or on a core buildup billed with a crown. CO is the contractual obligation group, so an in-network office generally cannot bill the patient for the bundled amount.
What does CO-45 mean on a dental EOB?
CO-45 means your fee is higher than the fee schedule or maximum the payer allows. For an in-network office it is the normal contractual write-off: the difference between your submitted fee and your contracted fee, which you adjust off and do not bill to the patient. It is not a denial.
What is the difference between CO and PR adjustment codes?
CO (contractual obligation) is an amount the office absorbs under its contract with the payer, such as a fee schedule write-off or a bundled service. PR (patient responsibility) is an amount the office may bill the patient, such as the deductible (PR-1), coinsurance (PR-2) or a service the plan does not cover. The group code tells you who owes the money, and the number tells you why.
What does PR-1 mean on a dental EOB?
PR-1 is the deductible. The plan applied part of the allowed amount to the patient’s deductible, so that amount moves to the patient balance. It is most common on the first claims of a new benefit year.
Are CARC codes the same on paper EOBs and ERAs?
Not always. Claim adjustment reason codes (CARCs) are the national X12 code set used on the electronic remittance advice, the 835 file. Many dental payers print their own remark codes on paper and portal EOBs instead, with a key on the statement. The meaning is often the same, but you have to read each payer’s key rather than assume.
Can I appeal a CO-97 bundling denial on a dental claim?
Sometimes. If the bundled procedure was genuinely separate, for example a core buildup that was needed because most of the tooth structure was missing, a narrative and radiographs or intraoral photos can support an appeal. If the payer’s policy treats the two codes as one service in every case, the appeal will not succeed and the amount is written off under an in-network contract.
