Call Vector Medical Billing
+1 (929) 539-7737
50States
Medical Billing Denial Codes: What CO, PR, and OA Mean
Every adjusted line on an 835 remittance carries a group code and a reason code. The group code (CO, PR, OA, or PI) says who carries the amount. The Claim Adjustment Reason Code (CARC) says why. A Remittance Advice Remark Code (RARC) often adds the detail that tells you what to fix. The meanings below are the X12 code descriptions.
98%Published NCR
24hClaim Submission
BAASigned with every client
AAPCCertified coders
AHIMACertified coders
E&OErrors and omissions insured
50 StatesRemote billing nationwide
835 remit
How to read a denial line
Group code first, then the reason code, then the remark code.
CO is contractual obligation: the practice cannot bill the patient for that amount. PR is patient responsibility: deductible, coinsurance, copay, or a non-covered service the patient agreed to pay for. OA is other adjustment, used for exact duplicates (18) and the effect of a prior payer (23). PI is a payer-initiated reduction. CR, an old corrections group, is not used in the 5010 transaction.
Some reason codes cannot stand alone. CARC 16 (missing information), 96 (non-covered charge), and 252 (attachment required) must come with at least one remark code, and the remark code is usually where the payer names what is missing.
Before you resubmit
- Read the group code: a CO amount is not billable to the patient
- Pull the remark code; it usually names the missing item
- Decide between a corrected claim, a reopening, and an appeal
- Log the code so the cause can be fixed before the next claim
Common denial codes and what fixes them
Reason code wording is from the X12 Claim Adjustment Reason Code list. The fix is what usually resolves it.
| Code | Meaning (X12) | What usually fixes it |
|---|---|---|
| CO-4 | The procedure code is inconsistent with the modifier used. | Check the modifier against the payer’s policy (for example 25, 59 or an X modifier, 26 or TC) and send a corrected claim. |
| CO-5 | The procedure code/type of bill is inconsistent with the place of service. | Match the place of service to where the service happened, such as 22 or 19 for a hospital outpatient department rather than 11. |
| CO-11 | The diagnosis is inconsistent with the procedure. | Code the diagnosis the note supports for that line and check the payer’s coverage policy for the procedure. |
| CO-16 | Claim/service lacks information or has submission/billing error(s). | Read the remark code, add the missing item, and resubmit as the payer’s rules require. |
| OA-18 | Exact duplicate claim/service. | Check claim status first. If the original is paid or pending, do nothing. If it needs changing, send a replacement claim (frequency code 7), not a copy. |
| CO-22 | This care may be covered by another payer per coordination of benefits. | Update coordination of benefits, bill the primary payer, then send the secondary claim with the primary’s remittance. |
| OA-23 | The impact of prior payer(s) adjudication including payments and/or adjustments. | Usually informational on a secondary claim. Post it; it is not an appeal. |
| CO-27 | Expenses incurred after coverage terminated. | Verify eligibility for the date of service and bill the active plan, or the patient if no coverage applies. |
| CO-29 | The time limit for filing has expired. | Appeal only with proof of timely submission, such as a clearinghouse acceptance report, or a valid delay reason. Medicare’s limit is 12 months from the date of service. |
| CO-45 | Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement. | A normal contractual write-off. Check the allowed amount against the contract to catch underpayments. |
| CO-50 | These are non-covered services because this is not deemed a ‘medical necessity’ by the payer. | Compare the note and diagnosis with the coverage policy (for Medicare, the LCD or NCD). Appeal with records, or bill the patient only if a valid ABN or payer waiver was signed. |
| CO-97 | The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated. | Check the NCCI edit. Use a modifier only when the service was truly separate and the note shows it. |
| CO-109 | Claim/service not covered by this payer/contractor. You must send the claim/service to the correct payer/contractor. | Send it to the right payer, for example the Medicaid managed care plan instead of fee-for-service Medicaid, or the correct Medicare contractor. |
| CO-151 | Payment adjusted because the payer deems the information submitted does not support this many/frequency of services. | Check units and frequency limits. Appeal with documentation if the frequency was medically necessary. |
| CO-167 | This (these) diagnosis(es) is (are) not covered. | Confirm the diagnosis is coded to full specificity and is covered for that service. |
| CO-197 | Precertification/authorization/notification/pre-treatment absent. | Request retro-authorization if the payer allows it, and fix the step at scheduling. See prior authorization. |
| CO-B7 | This provider was not certified/eligible to be paid for this procedure/service on this date of service. | An enrollment or credentialing gap. Check the effective date with the payer. See credentialing. |
| CO-252 | An attachment/other documentation is required to adjudicate this claim/service. | Send the record the remark code names through the payer’s attachment process. |
| PR-1, PR-2, PR-3 | Deductible amount; coinsurance amount; co-payment amount. | Not a denial. Bill the patient the amount shown. |
| PR-204 | This service/equipment/drug is not covered under the patient’s current benefit plan. | Patient responsibility when the plan excludes the service and the patient was told in advance. Check for a medical exception process first. |
Corrected claim, reopening, or appeal?
The fix depends on whether the claim was wrong or the payer was.
Corrected claim
When the claim itself was wrong: a code, a modifier, a missing identifier. Send a replacement claim (frequency code 7) or a new claim, as the payer requires. Do not send a duplicate.
Medicare reopening
For clerical errors and minor omissions on a Medicare claim. A provider can ask for a reopening within one year of the initial determination (42 CFR 405.980), usually by phone or the contractor’s portal.
Appeal
When the payer applied a rule wrongly or ignored documentation. Medicare’s first level, a redetermination, is due within 120 days of receiving the initial determination (42 CFR 405.942). Commercial deadlines follow the contract.
Working denials with Vector
What the monthly fee covers and what is priced separately.
Inside the monthly cycle
Denials on claims Vector submits are worked by reason code, appealed inside the payer’s window, and reported monthly by code and payer.
The fee is a percentage of net collections (flat or per claim in New York). See pricing.
Separate work
A backlog of denials older than the engagement, and payer underpayment projects, are scoped on their own: old A/R recovery and underpayment recovery.
Send us your denial list
Export the last 90 days of denials with their reason codes. We send back which ones are still recoverable, the fix for each code, and a written rate.
Written
Monthly rate
98%
Published NCR
50
US States
BAA
Every Client
Denial code questions
Short answers on reading remittance codes.
What is the difference between a CARC and a RARC?
A Claim Adjustment Reason Code (CARC) says why a line was paid differently than billed. A Remittance Advice Remark Code (RARC) adds detail, such as which item is missing. Some CARCs, including 16, 96, and 252, must come with at least one RARC.
What does CO mean on a remittance?
Contractual obligation. The amount is adjusted under the provider’s contract or a legislated fee schedule, and the practice cannot bill it to the patient.
Is CO-45 a denial?
No. CO-45 is the contractual write-off between the billed charge and the allowed amount. It is worth checking only to make sure the allowed amount matches the contract.
What does OA-18 mean?
Exact duplicate claim or service. X12 says to use code 18 with group code OA. Check the status of the original claim before doing anything; if it needs changing, send a replacement claim rather than another copy.
Can we bill the patient for a CO-50 denial?
Not for a Medicare patient unless a valid Advance Beneficiary Notice was signed before the service. Without one, the amount is the provider’s. Commercial plans follow their own waiver rules.
How long do we have to appeal a Medicare denial?
A redetermination must be filed within 120 days of receiving the initial determination. A reopening for a clerical error can be requested within one year.