Denial Knowledge Center

Work denials like a senior analyst

26 validated denial records and 26 guided troubleshooters. Each record carries the denial identifier, plain-language meaning, biller review, corrections, the resolution path, corrected claim vs appeal routing, payer overlays, department ownership, prevention controls, and escalation triggers.

D01
CO-16

Missing/Invalid/Incomplete Claim Information

Guided

The payer is saying the claim itself was incomplete or contained an error somewhere — a required field is missing, invalid, or does not match what the payer has on file.

Resolves: Billing

Troubleshoot
D02
CO-31

Patient Not Eligible / Cannot Be Identified as Insured

Guided

The payer cannot match the patient/member information on the claim to an active member on their system — either the ID is wrong, the patient is not covered by that plan, or an eligibility condition (waiting per…

Resolves: Registration

Troubleshoot
D03
CO-26CO-27

Coverage Not in Effect on Date of Service (Termination)

Guided

The payer's records show the patient's coverage ended before (CO-27) or had not started as of (CO-26) the date of service billed.

Resolves: Registration

Troubleshoot
D04
CO-22

Coordination of Benefits (COB) — Another Payer May Be Primary (CO-22)

Guided

CARC 22 means the payer believes another plan may be primary for this care, or the claim did not carry the prior payer's information. This is a payer-order and COB-data finding. It is a different finding from CARC 23, which reports the impact of a prior payer's adjudication.

Resolves: Billing

Troubleshoot
D26
OA-23

Impact of Prior-Payer Adjudication (OA-23 / narrow Medicare CO-23) & the "Recoupment Denial"

Guided

CARC 23 reports the impact of the prior payer's adjudication — payments and adjustments — and X12 defines it for use only with group code OA. On its own it is informational, not a denial, and not a reason to rebill. Some teams call it the "recoupment denial," but a true provider-level takeback appears separately in the 835 provider-level balance (PLB) section. Medicare also has a narrow conditional-payment implementation that uses CO-23 with M32 and N4.

Resolves: Billing

Troubleshoot
D05
CO-197CO-198

Authorization/Precertification Absent or Exceeded

Guided

The payer required prior authorization for this service and either did not receive one at all (CO-197) or the billed service/units/dates exceed what was actually authorized (CO-198).

Resolves: Precertification

Troubleshoot
D06
CO-288CO-287

Referral Absent or Exceeded

Guided

The plan (commonly an HMO/managed-care or Medicaid MCO plan requiring PCP referrals) either has no referral on file for this service or the service exceeds what the referral authorized.

Resolves: Billing

Troubleshoot
D07
CO-50

Medical Necessity Not Met

Guided

The payer's coverage policy (LCD/NCD or commercial medical policy) does not consider this service medically necessary for the diagnosis/circumstances billed.

Resolves: Denials

Troubleshoot
D08
CO-96

Noncovered / Statutorily Excluded Service

Guided

The service billed simply is not a covered benefit under this patient's plan (or, for Medicare, is excluded by statute) — this is different from a medical-necessity denial, which concerns whether a covered bene…

Resolves: Billing

Troubleshoot
D09
CO-97

Bundled / Incidental Procedure (NCCI Cross-reference for Inclusive Procedures)

Guided

The payer is not paying separately for this service because it considers it a component of, or incidental to, another procedure already billed and paid on the same claim or encounter — the payment for the small…

Resolves: Coding

Troubleshoot
D10
CO-18

Exact Duplicate Claim/Service

Guided

The payer's system has already received and processed an identical claim for this patient, date of service, and procedure — this submission is being treated as a repeat, not a new claim.

Resolves: Billing

Troubleshoot
D11
CO-29

Timely Filing Limit Expired

Guided

The claim was received by the payer after the deadline allowed in the plan/contract (or, for Medicare, after the 12-month statutory limit), so it is being denied for lateness rather than for any clinical or cod…

Resolves: Billing

Troubleshoot
D12
CO-11

Diagnosis Inconsistent with Procedure

Guided

The diagnosis code billed does not logically or per payer policy support the procedure code billed for this patient (e.g., a diagnosis that does not justify the specific test/procedure performed).

Resolves: Coding

Troubleshoot
D13
CO-4CO-182

Modifier Issues (Inconsistent or Invalid Modifier)

Guided

The modifier appended to the procedure code either doesn't make sense for that code, is not a valid modifier for the date of service, or a required modifier is missing entirely.

Resolves: Coding

Troubleshoot
D14
B7

Provider Not Certified/Eligible (Enrollment)

Guided

The payer's enrollment records show this provider was not enrolled, not credentialed with this specific plan, or not eligible to bill this specific service/specialty combination as of the date of service.

Resolves: Credentialing

Troubleshoot
D15
CO-185

Rendering Provider Not Eligible to Perform Service

Guided

The specific individual listed as having performed the service is not, per the payer's records, allowed to perform/bill that type of service — this differs from D14 (overall enrollment) in that it focuses on sc…

Resolves: Billing

Troubleshoot
D16
CO-206CO-207CO-208

NPI Missing, Invalid, or Not Matched

Guided

The claim is missing an NPI where one is required, the NPI is not in a valid format, or the NPI submitted does not match the provider name/role on the payer's file (including PECOS ordering/referring records, w…

Resolves: Billing

Troubleshoot
D17
CO-5CO-58

Place-of-Service Inconsistent or Invalid

Guided

The two-digit Place of Service (POS) code on the claim doesn't match the type of service billed, or the payer considers that setting invalid/inappropriate for this specific service.

Resolves: Billing

Troubleshoot
D18
CO-151

Frequency Limitation Exceeded

Guided

The payer's records show this service (or this many units of it) has already been provided more times, or in greater quantity, than the plan/coverage policy or NCCI MUE allows within the relevant time period.

Resolves: Coding

Troubleshoot
D19
CO-119CO-35CO-149

Benefit Maximum / Lifetime Maximum Reached

Guided

The patient's plan only covers a set amount/number of this service per period (CO-119) or ever (CO-35/CO-149), and that limit has already been used up.

Resolves: Billing

Troubleshoot
D20
CO-252

Missing Documentation / Attachment Required

Guided

The payer cannot finish processing this claim without additional supporting documentation (medical records, operative note, invoice, questionnaire, etc.) that either was never sent, was the wrong document, or w…

Resolves: HIM

Troubleshoot
D21
OA-133

Payer Processing — Claim Pending Further Review

Guided

The payer has not made a final decision yet — the claim/line is under active review (e.g., medical review, COB investigation, fraud/utilization review) and a corrected determination is expected later.

Resolves: Denials

Troubleshoot
D22
PR-1PR-2PR-3

Patient Responsibility (Deductible/Coinsurance/Copay)

Guided

The payer has processed and approved the claim; this specific dollar amount is the patient's contractual share of the cost (deductible, coinsurance, or copay), not a payer denial of the service itself.

Resolves: Patient Financial Services

Troubleshoot
D23
CO-45

Contractual Adjustment / Fee Schedule Write-off

Guided

The amount billed was simply higher than the contracted or fee-schedule allowed amount; the difference is a required write-off under the provider's contract with the payer, not something the patient owes (unles…

Resolves: Billing

Troubleshoot
D24
CO-140

Patient/Insured ID and Name Mismatch (Registration)

Guided

The insurance ID number and the patient/subscriber name submitted on the claim do not match what the payer has on file, so the payer's system cannot locate the correct member record to adjudicate the claim.

Resolves: Billing

Troubleshoot
D25
CO-109

Claim Sent to Wrong Payer/Contractor

Guided

The claim was submitted to a payer or contractor that does not have jurisdiction or responsibility for this patient, service, or claim type;

Resolves: Billing

Troubleshoot
Denial changes

What changed that affects denial work

Dates shown are the dates we record. Anything we do not record is marked “Not recorded.” Confirm every requirement against the payer’s current source and your contract.

Payer-published requirements in the denial overlays

Guided workflows
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Why work a denial through a guided workflow?

A reference page tells you what a code means. A guided workflow asks the few questions that separate one cause from another, then names the disposition, the transaction elements, the evidence to retain and the owner — so two analysts working the same denial reach the same defensible answer.

Find the real cause

One question at a time narrows a broad code down to the specific defect, instead of rebilling and hoping.

Know the right disposition

New original claim, corrected/replacement, void, secondary, appeal or no rebill — decided by the claim's actual lifecycle status.

Fix the right field

Each result names the exact CMS-1500, UB-04 or 837 elements to inspect and change, with step-by-step correction.

Avoid costly missteps

Explicit "do not do this" warnings, timely-filing risk, a pre-submit verification checklist, and prevention tips.

Zero PHI by design: every question is a fixed choice about what you verified in your own billing, EHR, or payer system. ClaimetryX never asks for patient, member, or claim identifiers. Ask ClaimetryX is a separate optional $5/month add-on and is not required.

Validated ClaimetryX Source — Denial Management Knowledge Base, 2026 Research Edition

Research date August 18, 2026. CARC/RARC combinations and payer processes vary. Always check the specific remittance advice and the payer's current requirements before acting on any denial.