Claim Denial Codes Explained

Procedure Code and Modifier Do Not Match

The CO-4 denial code means the payer found a mismatch between the procedure code and the modifier on the claim line - either the modifier you appended does not make sense with that CPT/HCPCS code, or a modifier the code requires is missing. It is a coding-edit denial, not a coverage decision, so the fix is almost always to correct the modifier and resubmit.

Diagnosis Inconsistent With the Procedure

The CO-11 denial code means the payer decided the diagnosis code on the claim does not match or support the procedure that was billed. In other words, the ICD-10 code and the CPT/HCPCS code tell conflicting stories - for example, a knee procedure billed with only a shoulder diagnosis. The denial is about the pairing, not necessarily about coverage, so it is usually correctable.

Authorization Number Missing or Invalid

The CO-15 denial code means an authorization was required and the number submitted on the claim is missing, wrong, or does not cover the service, provider, or dates billed. Unlike CO-197 (no authorization obtained at all), CO-15 usually means an authorization exists somewhere - it just was not transmitted correctly or does not line up with what was billed.

Claim Lacks Information or Has a Billing Error

The CO-16 denial code means the claim could not be processed because it is missing information or contains a submission or billing error. CO-16 is a catch-all: it never tells the whole story by itself. The remittance advice pairs it with remark codes (RARCs like M76, M51, N290, or N382) that identify the specific missing or invalid element, so reading the remark codes is step one of working the denial.

Duplicate Claim or Service

The CO-18 denial code means the payer identified the claim or service line as an exact duplicate of one it already received. Duplicate logic typically compares patient, provider, date of service, procedure code, and billed amount - if all match an earlier claim, the new one is denied automatically. Medicare reports duplicates under group code OA (as OA-18), but many commercial payers use CO-18 for the same reason code.

Another Payer May Be Responsible (Coordination of Benefits)

The CO-22 denial code means the payer believes this care may be covered by another payer under coordination of benefits (COB) - in other words, you billed them as primary but their records say someone else should pay first. The claim will not be considered until the correct primary payer processes it or the COB information is straightened out.

Covered by a Capitation Agreement or Managed Care Plan

The CO-24 denial code means the charges are covered under a capitation agreement or managed care plan - the payer you billed is saying the service is already paid for through a different arrangement. In Medicare billing this most often means the patient is enrolled in a Medicare Advantage plan, so the claim must go to that plan instead of traditional Medicare.

Timely Filing Limit Expired

The CO-29 denial code means the claim arrived after the payer's timely filing deadline - the window each payer allows between the date of service and claim submission. Medicare allows 12 months from the date of service; commercial payers commonly allow anywhere from 90 days to a year, set by contract. Because the money is a provider write-off unless you can prove timely submission or qualify for an exception, prevention matters more than cure for this denial.

Patient Cannot Be Identified as Insured

The CO-31 denial code means the payer cannot identify the patient as its insured - the person on the claim does not match an active member in its records. It is a close cousin of remark code N382 (invalid patient identifier), but as a reason code it carries the denial itself: coverage could not be confirmed for this person on this date of service.

Charge Exceeds the Fee Schedule or Contracted Rate

The CO-45 adjustment code means the billed charge exceeded the payer's fee schedule, maximum allowable, or contracted rate - the payer paid its allowed amount and CO-45 accounts for the difference. Strictly speaking it is a contractual adjustment, not a denial: seeing CO-45 on a paid line is completely normal. It only needs investigation when the allowed amount looks wrong for your contract.

Not Deemed Medically Necessary

The CO-50 denial code means the payer determined the service was not medically necessary as billed. In practice, the payer is rarely judging the medicine itself - its edits compared the ICD-10 diagnosis codes on the claim against a coverage policy (for Medicare, an LCD or NCD) and did not find a diagnosis that supports the service. That makes CO-50 as much a coding and documentation denial as a clinical one.

Included in Payment for Another Service (Bundled)

The CO-97 denial code means the benefit for this service is already included in the payment for another service that has been adjudicated - in short, the line is bundled. Typical examples are services billed during a surgical global period and procedure combinations where one code's payment includes the other's work. The decision to make is whether the bundling is correct (write-off) or whether the service was truly separate and needs a modifier and appeal.

Related or Qualifying Claim Not Found

The CO-107 denial code means the claim references or depends on another service that the payer could not identify - the related or qualifying claim was not found or was not linked properly. It shows up when a service only makes sense in combination with another one: add-on codes without their primary procedure, or claims that must match a companion claim in the payer's system.

Wrong Payer or Contractor for This Claim

The CO-109 denial code means the claim went to a payer or contractor that is not responsible for it - the service is not covered by this payer, and the claim must be sent to the correct one. It is a routing problem, not a coverage decision. In Medicare billing it commonly appears when services overlap a Part A stay (for example, outpatient services during a skilled nursing facility stay that belong to the SNF under consolidated billing) or when the claim belongs with a different contractor or plan entirely.

Frequency of Services Not Supported

The CO-151 denial code means the payer adjusted the claim because the information submitted does not support the number of units or the frequency of the service billed. The payer is not questioning whether the service is covered - it is questioning how many or how often. Medicare contractors commonly attach this reasoning to Medically Unlikely Edit (MUE) unit limits and frequency-limited services like screenings and certain injections.

Diagnosis Not Covered

The CO-167 denial code means the diagnosis (or diagnoses) on the claim is not covered by the payer - the ICD-10 code billed falls outside what the plan or policy covers for that service. It overlaps with CO-50, but where CO-50 frames the problem as medical necessity, CO-167 points squarely at the diagnosis code itself: either the wrong code went on the claim, or the documented condition is genuinely excluded from coverage.

Prior Authorization Absent

The CO-197 denial code means the service required precertification, prior authorization, or advance notification and the payer has no record of one. Unlike CO-15 (an authorization exists but does not match), CO-197 says the approval simply is not there. Because the CO group makes this a provider write-off, the practical paths are retroactive authorization, appeal with good cause, or process fixes to stop the next one.

Procedure Not Paid Separately

The CO-234 denial code means this procedure is not paid separately - its payment is packaged into another service or payment on the claim. Payers are required to send a remark code with it explaining the specific packaging rule, so the RARC on the remit tells you which bundling policy applied. A frequent Medicare pairing is remark code M2 (not paid separately when the patient is an inpatient).

NCCI Procedure-to-Procedure Edit

The CO-236 denial code means the procedure combination billed for the same day is not separately payable under the National Correct Coding Initiative (NCCI) or a similar payer coding policy. NCCI procedure-to-procedure edits define code pairs where one code's work is considered part of the other's. Whether you can be paid depends on the edit's modifier indicator: some pairs allow a bypass modifier when the services were truly distinct, and some never do.

Documentation Required to Process the Claim

The CO-252 denial code means the payer needs an attachment or additional documentation before it can finish adjudicating the claim. It is a request, not a final coverage decision - the claim is parked until you supply what was asked for. The accompanying remark code usually specifies what to send: operative notes, invoices for drugs or devices, medical records, or a required certificate.

Provider Not Certified or Eligible for This Service on This Date

The CO-B7 denial code means the provider was not certified or eligible to be paid for this procedure or service on the date it was performed. The service itself may be perfectly coverable - the problem is the provider's status on that date: enrollment not yet effective, credentialing lapsed, or a required certification (such as CLIA for lab tests) missing or not matching the service billed.

Patient Is Enrolled in Hospice

The CO-B9 denial code means the patient is enrolled in a hospice program, and the payer considers the billed service part of the hospice benefit - services related to the terminal illness are paid through the hospice, not fee-for-service Medicare or the standard plan. Services unrelated to the terminal condition remain billable, but the claim must say so with the right modifier.

Required Qualifying Service Missing

The CO-B15 denial code means this service is payable only when a qualifying service has been received and covered, and the payer has not found that qualifying service. It is the dependency denial: add-on codes without their primary procedure, or services that require a covered antecedent (an initial service before a subsequent one) that is missing, denied, or not yet on file.

Deductible Amount

The PR-1 code means the amount was applied to the patient's deductible - the portion of allowed charges the patient must pay each benefit period before the plan starts paying. PR-1 is not a denial and nothing about the claim is wrong: the payer processed it, applied the allowed amount to the deductible, and assigned that amount as patient responsibility.

Coinsurance Amount

The PR-2 code means the amount is the patient's coinsurance - the percentage of the allowed amount the patient owes after the deductible is met (for example, 20% under Medicare Part B). Like the other PR cost-share codes, it is not a denial: the claim paid, and PR-2 is simply the patient's calculated share.

Copayment Amount

The PR-3 code means the amount is the patient's copayment - the fixed dollar amount their plan assigns for that type of visit or service (for example, a set office-visit or emergency-department copay). It is not a denial; the payer is telling you which part of the allowed amount belongs to the patient.

Routine or Screening Service Not Covered

The PR-49 denial code means the service was denied because it is a routine or preventive exam, or a screening procedure done in conjunction with one, and the plan does not cover it as billed. The same reason code appears as CO-49 with some payers. These denials frequently hinge on how the encounter was coded: whether the visit was truly routine, or a diagnostic service that got coded as screening (or vice versa).

Non-Covered Charges

The PR-96 denial code means the charge is not covered - the payer classifies the billed item or service outside the benefits it pays for. Payers must include a remark code with it identifying the specific reason (a benefit exclusion, a statutory exclusion, or plan rules), so the RARC alongside PR-96 does most of the explaining. Under the PR group the amount falls to the patient; the same reason code with CO in front makes it a provider write-off instead.

Not Covered Under the Patient's Current Benefit Plan

The PR-204 denial code means the service, equipment, or drug is not covered under the patient's current benefit plan - the plan they are enrolled in right now simply does not include this item as a benefit. Where PR-96 flags a non-covered charge in general, PR-204 points specifically at the patient's plan design: another plan might cover it, but this one does not.

Exact Duplicate Claim or Service

The OA-18 denial code means the payer received an exact duplicate of a claim or service line already in its system - same patient, provider, date of service, procedure, and charge. The standard assigns duplicates to group code OA (neither provider nor patient liability in the usual sense), which is how Medicare reports them; some commercial payers report the same reason as CO-18. The first move is always to find out what happened to the original claim.

Prior Payer Adjudication Impact (Secondary Claims)

The OA-23 code shows the impact of a prior payer's adjudication - the payments and adjustments the primary insurance already made - on a secondary or tertiary claim. It is bookkeeping, not a denial: the secondary payer uses OA-23 to account for what the primary already handled before calculating its own payment. Seeing OA-23 on a secondary remit is expected.

Documentation Does Not Support the Level of Service

Remark code M25 means the information furnished does not substantiate the level of service billed - the payer reviewed the claim (and any records) and concluded the documentation supports a lower level than the code submitted. It typically accompanies downcoding of evaluation and management (E/M) visits or payment at a reduced level, and it comes with appeal rights if you believe the billed level was right.

Missing or Invalid Procedure Code

Remark code M51 means one or more procedure codes on the claim are missing, incomplete, or invalid - the CPT/HCPCS code could not be processed as submitted. It almost always rides along with reason code CO-16 (claim lacks information) and turns that generic rejection into a specific instruction: fix the procedure code and resubmit.

Missing or Invalid Diagnosis

Remark code M76 means the diagnosis or condition information on the claim is missing, incomplete, or invalid - an ICD-10 code the payer could not accept as submitted. Paired almost always with CO-16, it is one of the most common purely ICD-10-driven rejections: the code is truncated, deleted, non-billable, or absent where one is required.

Missing or Invalid Place of Service

Remark code M77 means the place of service (POS) information on the claim is missing, incomplete, invalid, or inappropriate - the two-digit POS code either is not there, is not a real code, or conflicts with the service billed. Like the other M-series remark codes it usually accompanies CO-16, pointing you at the exact field to fix.

Primary Payer Information Missing on a Secondary Claim

Remark code MA04 means the claim was billed as secondary, but the payer cannot consider it because the primary payer's identity or payment information is missing or unreadable. The secondary payer needs to know who the primary was and what it paid or adjusted before calculating its own payment - without that, the claim stalls.

Claim Unprocessable - Fix and Resubmit (No Appeal Rights)

Remark code MA130 means the claim contains incomplete or invalid information and is being returned as unprocessable - it was never adjudicated on its merits, so no appeal rights attach. The only path forward is correcting the error and submitting a new claim. Other remark codes on the same remittance identify what exactly was incomplete or invalid.

Check the Plan's Benefit Documents for Restrictions

Remark code N130 tells you to consult the patient's plan benefit documents or guidelines for the restrictions that affected this service - the plan applied a benefit-level rule (a limitation, exclusion, or condition) and is pointing you to the plan language rather than spelling it out on the remit. It arrives alongside a reason code (often PR-96, PR-204, or CO-50) that carries the actual dollars.

Payer Requested Information From the Patient

Remark code N179 means the payer has requested additional information from the member - the patient, not the provider - and will reconsider the charges when it arrives. Claims sit in this state when payers need accident questionnaires, other-insurance surveys, student status confirmation, or similar member-supplied details. The risk is that patients ignore payer mail, leaving the claim in limbo until it eventually denies.

Missing or Invalid Rendering Provider Identifier

Remark code N290 means the rendering provider's primary identifier - in practice, the NPI - is missing, incomplete, or invalid on the claim. The payer cannot tie the service to a recognized rendering provider, so the claim stops. It typically arrives with CO-16 and is a data correction: put the right NPI in the right field and resubmit.

Missing or Invalid Patient Identifier

Remark code N382 means the claim's patient identifier is missing, incomplete, or invalid - the member ID, Medicare Beneficiary Identifier (MBI), or other subscriber number does not match a person in the payer's system. Nothing about the services is being judged; the payer simply cannot find the patient. It is one of the most preventable rejections in the revenue cycle.