CO-16 — Claim or service lacks information
What it means: The insurer is missing a piece of data it needs to adjudicate the claim. Usually paired with a Remark code (RARC) that names the missing item.
Common causes: Missing modifier on a CPT code, no referring NPI, no primary-payer EOB on file (for secondary claims), missing accident details, or supporting documentation that wasn't attached.
Appeal strategy: Read the paired Remark codes (N-series) carefully — they spell out exactly what's missing. Submit the missing item and re-bill or appeal. Usually administratively resolved in one cycle, not a contested clinical appeal.
CO-18 — Duplicate claim/service
What it means: The insurer thinks this exact claim has already been adjudicated, or that the service was already paid under a different code on the same date.
Common causes: Same claim resubmitted (by the provider's billing software auto-resubmitting), bilateral procedure billed without ‐50 modifier, or two distinct services with overlapping code descriptions.
Appeal strategy: If it's truly a duplicate, no action needed. If two services were distinct (same day, different sites, different times), appeal with documentation: timestamps, anatomical locations, separate operative notes.
CO-22 — This care may be covered by another payer
What it means: The insurer believes another insurance plan is responsible for paying first (coordination of benefits).
Common causes: Stale COB info on file, ex-spouse's plan still listed as primary, Medicare-vs-employer plan order disputes, auto/workers-comp claims that the insurer thinks should go to the other carrier first.
Appeal strategy: Call the member services line, update the COB record, then have the provider re-bill. If the insurer's order-of-benefits determination is wrong, send the SPD section that names the actual primary plan.
CO-29 — The time limit for filing has expired
What it means: The claim was submitted past the insurer's timely-filing window. Each plan sets its own (90 days to 1 year is typical).
Common causes: Provider's billing department was slow, claim was bouncing between primary and secondary payers, or you didn't know you had insurance at the time of service.
Appeal strategy: Hard but not impossible. Show proof of timely submission (claim receipt date stamps, payer rejection letters with dates, original submission EDI logs) or document a "good cause" exception — ERISA plans sometimes allow tolling when there's evidence the plan was on notice.
CO-45 — Charge exceeds fee schedule/maximum allowable
What it means: The provider billed more than what the insurer's negotiated rate (or "usual and customary" amount for out-of-network) allows. This is a contractual adjustment, not a denial of the service.
Common causes: Standard billing — almost every in-network claim has some CO-45 adjustment. The contracted rate is always less than the billed rate. For OON providers, the insurer applied its UCR rate instead of the billed amount.
Appeal strategy: Generally not appealable for in-network claims (it's contractual) — the provider has to absorb it. For out-of-network surprise-bill scenarios under the federal No Surprises Act (2022), you may have standing to dispute via IDR. Talk to the billing office before paying anything beyond your in-network cost-share.
Highly appealable
CO-50 — Not deemed a "medical necessity"
What it means: The insurer's medical reviewer decided your care didn't meet their internal medical-necessity criteria. This is a clinical judgment, not a coverage exclusion — which is exactly why it's appealable.
Common causes: The reviewer applied MCG or InterQual criteria mechanically without seeing the full clinical picture; the procedure was performed without documentation of conservative-therapy failures the insurer wanted to see first; the diagnosis on the claim didn't match the indication on the insurer's medical policy.
Appeal strategy: Submit a Letter of Medical Necessity from the treating physician citing specific clinical findings, prior conservative treatment, and the standard-of-care guideline (AMA, specialty society, NCD/LCD if Medicare). Attach all clinic notes, imaging reports, lab work, and any prior trial-and-failure documentation. CO-50 has one of the highest appeal-overturn rates of any denial code — HHS OIG found 82% of appealed Medicare Advantage prior-auth denials were overturned (read our full CO-50 appeal guide).
CO-96 — Non-covered charges
What it means: The service is excluded under the patient's specific benefit plan. Unlike CO-50, which is a clinical judgment, CO-96 says the service is simply not a covered benefit.
Common causes: Cosmetic procedures, experimental/investigational services, weight-loss interventions, fertility treatments, vision/dental on a medical-only plan, or any service explicitly listed as excluded in the Summary Plan Description.
Appeal strategy: Read your SPD (Summary Plan Description) exclusion list carefully. If your service is on it, the appeal is uphill — argue that the procedure is reconstructive (not cosmetic) or medically necessary (not elective) with physician documentation. Some employers offer exception processes outside the standard appeal flow.
Often appealable
CO-97 — Bundled / payment already included
What it means: The insurer says the benefit for this service is already included in payment for another procedure on the claim. Common bundling examples: surgical assistant services bundled into the surgeon's fee; post-op visits bundled into the global surgery period.
Common causes: NCCI (National Correct Coding Initiative) edits applied automatically; missing modifiers (-59 distinct procedural service, -25 significant E/M same day); or a legitimate disagreement about whether two services overlap.
Appeal strategy: If a modifier was missing, the provider should re-bill with the correct modifier rather than appeal. If the bundling determination is wrong, appeal with the operative note showing the procedures were distinct (different anatomical sites, separate sessions, or unrelated to the global). CMS publishes the NCCI manual — cite the specific edit being misapplied.
CO-109 — Claim/service not covered by this payer
What it means: Wrong payer routing. The service falls under a different benefit (e.g., dental on a medical-only plan), a different payer entirely (e.g., Medicare vs. employer plan), or out-of-network rules.
Common causes: Patient eligibility wasn't current at date of service, wrong insurer billed, dental procedure billed under medical, vision services on medical-only plan.
Appeal strategy: Confirm eligibility for the date of service. If you have a Medicare Advantage plan, original Medicare won't pay — the MA plan must. If the provider billed the wrong payer, have them re-bill the correct one.
CO-119 — Benefit maximum reached
What it means: The plan limit (visit count, dollar cap, or session limit) for this benefit has been used up for the current period.
Common causes: PT/OT visit caps (e.g., 30 visits/year), mental-health session limits (parity issues here are appealable!), durable medical equipment yearly caps, prescription quantity limits.
Appeal strategy: For mental health caps, cite the Mental Health Parity and Addiction Equity Act — behavioral health limits that are more restrictive than medical-surgical limits are illegal. For PT/OT, request an extension with continued-progress documentation. For prescription quantity limits, request a tier exception or formulary override.
Often appealable
CO-167 — Diagnosis not covered
What it means: The ICD-10 diagnosis code on the claim doesn't match what the insurer's medical policy lists as a covered indication for the billed CPT.
Common causes: Billing department selected a less-specific diagnosis code; the patient's actual covered diagnosis isn't documented in the chart; insurer's medical policy is narrower than current standard of care.
Appeal strategy: Request the provider re-bill with a more specific or appropriate diagnosis code that IS on the insurer's covered list (if clinically supported). If the diagnosis is correct and SHOULD be covered, appeal with peer-reviewed literature showing the indication is standard of care — many insurer medical policies lag the literature by 2-3 years.
Often appealable
CO-197 — Prior authorization absent
What it means: The service required pre-authorization (or pre-certification, or pre-notification), and one wasn't on file at the time of service.
Common causes: Provider's office missed the auth requirement, auth was attempted but timed out, the auth covered a different code or date, or the service was urgent/emergent and an after-the-fact auth wasn't requested.
Appeal strategy: If the service was emergent or urgent, ACA-compliant plans can't deny on prior-auth grounds — cite 29 CFR §2590.715-2719 and your plan's own emergency-services language. For non-urgent cases, request a retrospective authorization with full clinical documentation. Many insurers will grant it administratively if the service would have been authorized had it been requested up-front.
CO-198 — Precertification/notification absent
What it means: Variant of CO-197. Often used when the auth lapsed mid-treatment, covered a different procedure than what was actually performed, or didn't include the specific provider who rendered the service.
Appeal strategy: Same general approach as CO-197 — document the medical necessity and request a retrospective authorization. If the auth was issued for the wrong code/provider, send the original auth letter alongside the operative note to show the service performed was the equivalent.
PR-1 — Deductible
What it means: Patient owes this amount because the annual deductible hasn't been fully met yet.
Appeal strategy: Generally not appealable — this is the patient's contractual share. Verify the deductible amount the insurer applied is correct (check your benefit summary), and confirm the date of service falls in the correct plan year.
PR-2 — Coinsurance
What it means: Patient's share of the negotiated rate after the deductible is met. Usually expressed as a percentage (e.g., 20% coinsurance).
Appeal strategy: Generally not appealable. Verify the in-network rate was applied (not out-of-network or UCR), and that the coinsurance percentage matches your plan.
PR-3 — Co-payment
What it means: Flat patient fee per visit/service (e.g., $25 PCP, $50 specialist). Distinct from coinsurance.
Appeal strategy: Generally not appealable. Common errors: specialist copay applied to a primary-care visit, or copay applied when the visit should have been preventive care (which under ACA has $0 cost share for covered preventive services).
PR-204 — Service/equipment not covered under patient's plan
What it means: The service, drug, or equipment is not a covered benefit under this specific plan — not based on medical necessity, but based on the plan's covered benefits list.
Common causes: Off-formulary medications, experimental procedures, services classified as "convenience items" by the insurer, brand-name drug when generic exists.
Appeal strategy: Request a formulary/tier exception with physician documentation showing why the alternative isn't appropriate. Many plans have a "medical exception" process separate from the standard appeal. For experimental/investigational denials, cite FDA approval status, NCCN guidelines, or peer-reviewed literature.
PR-242 — Services not provided by network/primary care
What it means: Out-of-network or no-referral-on-file in an HMO/EPO plan. Network adequacy is part of why this code shows up.
Common causes: Emergency room visit at OON facility, specialist seen without PCP referral, lab/imaging done by OON vendor at an in-network facility.
Appeal strategy: For emergencies, federal No Surprises Act and prudent-layperson standard apply — OON denials for emergency care are appealable as a matter of federal law. For "in-network facility, OON provider" scenarios (radiologist, anesthesiologist), No Surprises Act covers most. For missing referrals, request a retroactive referral from the PCP — many plans honor this if requested within 30 days.
N130 — Consult plan benefit documents
What it means: This is a Remark Code (RARC), not a primary denial reason. It's a pointer telling you to consult your Summary Plan Description for restrictions on the service.
What to do: N130 always accompanies another code (typically CO-50, CO-96, or PR-204). The other code is the actionable one — N130 just confirms the insurer is referencing a benefit document, not an external rule.
N362 — Number of days/units exceeds maximum
What it means: Remark Code paired with CO-119 (benefit max reached) or similar. The specific service has a units-per-claim or days-per-period limit that was exceeded.
What to do: Request the specific limit from the insurer in writing. For PT/OT/mental health, parity and continued-progress documentation can support an extension. For DME, document the medical need for the higher quantity.