Denial Code Lookup

“Claim/service lacks information or has submission/billing error(s) which is needed for adjudication. Do not use this code for claims attachment(s)/other documentation. At least one Remark Code must be provided.”

This is the single most common denial code in US medical billing. CO-16 fires when the insurance carrier's adjudication system detects that your claim submission is missing a required data field, contains a formatting inconsistency, or has a structural billing error that prevents the payer from processing the line item. Common triggers include missing or invalid patient demographics (date of birth, subscriber ID), absent referring provider NPI on specialist claims, incorrect place of service codes, invalid CPT/HCPCS modifiers, or submitting a claim with a rendering provider not credentialed under the billed Tax ID. Because this is a Contractual Obligation denial, the financial loss falls entirely on the provider — you cannot bill the patient for this balance.

“The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated. Note: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.”

CO-97 means the payer determined that one of your billed procedure codes is a component part of another code you submitted on the same claim, and they've bundled the lesser code into the payment of the primary code. This denial is driven by the National Correct Coding Initiative (NCCI) edit tables maintained by CMS, which define code-pair relationships. For example, if you bill a comprehensive surgical code alongside a component code that is inherently included in that procedure, the payer will deny the component code under CO-97. This also commonly triggers when modifier -59 (Distinct Procedural Service) or its X{EPSU} subset modifiers are missing to indicate that two procedures were genuinely performed at separate anatomical sites or during distinct encounters.

“The diagnosis is inconsistent with the procedure. Note: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.”

CO-11 indicates the payer's medical policy engine determined that the ICD-10-CM diagnosis code linked to the procedure does not establish medical necessity for the service performed. Insurance carriers maintain Local Coverage Determinations (LCDs) and National Coverage Determinations (NCDs) that map which diagnosis codes are considered medically justified for a given CPT/HCPCS procedure. If your claim's diagnosis-to-procedure pairing falls outside those coverage articles, the payer denies under CO-11. This frequently happens with lab orders that use symptom-level ICD-10 codes instead of specific disease codes, or with imaging studies where the diagnosis doesn't demonstrate the clinical severity threshold the payer requires.

“The time limit for filing has expired.”

CO-29 is a hard denial indicating that your claim was submitted after the payer's contractual timely filing deadline. Every insurance carrier contract specifies a maximum number of days from the date of service (or date of knowledge of the primary payer's adjudication) within which you must submit a clean claim. For Medicare, the standard window is 12 months. For most commercial payers, it ranges between 90 and 365 days, depending on the contract. Once this deadline passes, the payer is under no obligation to process the claim, and because this is a CO-group denial, you cannot transfer the balance to the patient. The financial loss is permanent unless you can successfully prove timely filing through an appeal with documentation such as a clearinghouse transmission receipt or a prior claim acknowledgment (277CA).

“Deductible Amount.”

PR-1 is not a denial — it is a patient responsibility adjustment indicating that the payer applied all or part of the allowed amount toward the patient's remaining annual deductible. Under the patient's benefit plan, a deductible is the dollar amount the insured individual must pay out-of-pocket for covered services before the insurance plan begins paying its share. PR-1 tells you that the insurance carrier has processed the claim, confirmed the service is covered, calculated the contracted allowed amount, and determined that the patient has not yet satisfied their deductible for the plan year. The full adjusted amount now becomes a legitimate patient balance that your billing office should collect from the patient or their guarantor.

“Coinsurance Amount.”

PR-2 indicates the payer has processed the claim, applied the contracted allowed amount, and determined that a percentage-based cost-sharing obligation — coinsurance — applies to the patient under their benefit plan. Coinsurance is the patient's share of the allowed amount after the deductible has been met, expressed as a percentage (e.g., the plan pays 80% and the patient owes 20%). This is a standard patient responsibility adjustment and is fully billable to the patient. The amount shown represents the patient's calculated coinsurance portion based on the payer's fee schedule and the patient's specific plan design.

“Co-payment Amount.”

PR-3 is a patient responsibility adjustment indicating that a fixed-dollar copayment amount applies to this service under the patient's benefit plan. A copayment is a flat fee (e.g., $25 for a primary care visit, $50 for a specialist visit) that the patient is required to pay at the time of service or upon receipt of a statement. Unlike coinsurance, which is a percentage, a copay is a predetermined dollar amount that does not vary with the cost of the service. If your front desk did not collect the copay at check-in, this adjustment tells you to bill the patient for the outstanding amount.

“The impact of prior payer(s) adjudication including payments and/or adjustments. Note: This code is not to be used by the first payer on a claim. This group code is to be used by subsequent payers only.”

When OA-23 appears on a secondary or tertiary payer's remittance, it indicates that this payer is adjusting payment based on the actions taken by the primary insurance carrier. The secondary payer is referencing the primary payer's adjudication — including whatever the primary paid, denied, or adjusted — and applying its own coordination of benefits (COB) rules to determine what it owes. However, in common practice many payers also use the CARC 23 code in conjunction with authorization-related denials, where the adjustment reflects that required prior authorization, precertification, or pre-approval was not obtained before the service was rendered. When this happens, the financial disposition depends on the group code: under OA, the liability is ambiguous and may require further investigation to determine whether the provider or the patient bears the cost.