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Medical Billing Denial Code Lookup

Search any CARC denial code to see what it means and exactly what to do next. Covers the most common claim adjustment reason codes billers meet every day — free, no signup.

Showing all 25 codes

CODE	WHAT IT MEANS	WHAT TO DO
CO-4 Coding	Procedure code inconsistent with the modifier used, or a required modifier is missing.	Check the modifier against the CPT and payer policy. Common with modifier 25, 59 and the X-series. For how 59 and 52 apply to cystoscopy claims, see urology billing services. Correct and resubmit as a corrected claim.
CO-11 Coding	The diagnosis is inconsistent with the procedure.	The ICD-10-CM code does not support medical necessity for the CPT billed. Review documentation and recode, or appeal with clinical notes.
CO-16 Submission	Claim or service lacks information, or has a submission/billing error.	Almost always paired with a RARC that names the missing element. Read the RARC, supply the missing data and resubmit.
CO-18 Duplicate	Exact duplicate claim or service.	Check whether the original paid. If this is a genuinely distinct service on the same day, append modifier 76, 77 or 59 as appropriate and resubmit with documentation.
CO-22 COB	This care may be covered by another payer per coordination of benefits.	Verify primary vs secondary on file. Update COB with the payer and rebill with the primary EOB attached.
CO-23 COB	Impact of prior payer adjudication, including payments and adjustments.	Secondary claim adjustment. Confirm the primary payment posted correctly before writing anything off.
CO-27 Eligibility	Expenses incurred after coverage terminated.	Eligibility was not verified, or terminated mid-episode. Check for a new plan and rebill; otherwise transfer to patient responsibility if contractually allowed.
CO-29 Timely filing	The time limit for filing has expired.	Usually unappealable unless you can prove timely submission. Pull the clearinghouse acceptance report as proof and appeal. See our timely filing limits by payer and state before resubmitting. Use our appeal letter templates to draft the appeal.
CO-45 Contractual	Charge exceeds fee schedule, maximum allowable, or contracted amount.	This is the contractual write-off, not a true denial. Verify it matches your contracted rate - if it is lower, you are being underpaid and should appeal.
CO-50 Medical necessity	Not deemed a medical necessity by the payer.	Check the payer LCD/NCD policy. Appeal with clinical documentation supporting necessity, or issue an ABN going forward.
CO-96 Coverage	Non-covered charge(s).	Review the RARC for the reason. If the service is excluded from the plan, transfer to patient with proper prior notice.
CO-97 Bundling	Benefit for this service is included in the payment for another service already adjudicated.	Bundling edit. Check NCCI edits - if the services were genuinely distinct, append modifier 59 or an X-modifier and appeal with documentation. For how this applies to ECG, echo and other cardiology tests, see our cardiology billing services.
CO-109 Wrong payer	Claim not covered by this payer or contractor.	Sent to the wrong payer or wrong contractor jurisdiction. Verify the payer ID and rebill to the correct entity.
CO-151 Frequency	Payer deems the information submitted does not support this many services.	Frequency or units exceed policy. Verify units billed, check policy limits, and appeal with documentation if clinically justified.
CO-167 Diagnosis	This diagnosis is not covered.	The diagnosis is excluded under the plan or policy. Verify coding accuracy first; if correct, the service may be patient responsibility.
CO-197 Authorization	Precertification, authorization or notification absent.	Check whether an auth existed but was not on the claim. If so, appeal with the auth number. If none was obtained, request a retro-auth where the payer allows it.
CO-B7 Credentialing	Provider was not certified or eligible to be paid for this procedure on this date of service.	Credentialing or enrollment gap. Verify the effective date with the payer and rebill once the provider is active; this is why enrollment lapses are expensive.
PR-1 Patient responsibility	Deductible amount.	Patient deductible. Bill the patient. Verify against the EOB before statementing.
PR-2 Patient responsibility	Coinsurance amount.	Patient coinsurance. Bill the patient per the EOB.
PR-3 Patient responsibility	Co-payment amount.	Copay - ideally collected at the point of service. Bill the patient if not collected.
PR-204 Coverage	Service, equipment or drug is not covered under the patient current benefit plan.	Non-covered benefit. Patient responsibility if you gave appropriate advance notice; otherwise it may be a write-off.
CO-15 Authorization	The authorization number is missing, invalid, or does not apply.	Verify the auth number and date span, then resubmit as a corrected claim with the correct authorization.
CO-31 Eligibility	Patient cannot be identified as our insured.	Demographic or member ID mismatch. Re-verify eligibility, correct the member ID or date of birth, and rebill.
CO-140 Eligibility	Patient/Insured health identification number and name do not match.	Name and ID mismatch. Verify against the insurance card and correct the registration record before rebilling.
CO-181 Coding	Procedure code was invalid on the date of service.	The CPT/HCPCS was deleted or not yet effective for that date. Recode using the code valid on the DOS and resubmit.

Denials keep coming back? That is a workflow problem, not bad luck.

Looking up the code fixes one claim. Fixing the cause fixes every claim after it.

When the same payer denies the same code month after month, the fix belongs at the front of the revenue cycle — an eligibility check, a coding rule, an authorisation step. BilNow’s medical coding services and outsourced medical billing services work denials to root cause inside your existing EHR, from 2.7% of collections with no setup fee. Many denials start with a gap in the visit record, so check yours against our free superbill template. Related: A/R recovery, billing audits, and pricing.

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Denial codes shown are standard X12 Claim Adjustment Reason Codes (CARC). Payers may pair them with Remittance Advice Remark Codes (RARC) that give more detail. Always check the specific payer policy — this tool is a reference, not payer-specific advice.