Claim Denial Codes Explained: What CO-16, CO-50, CO-197, PR-1 and Others Mean and How to Fix Them

A denial code has two parts: a group code (CO, PR, OA or PI) that says who is responsible for the amount, and a claim adjustment reason code (CARC) number that says why. CO-16 means information is missing, CO-50 means the payer says the service was not medically necessary, CO-197 means an authorization was missing, and PR-1 is simply the patient’s deductible. The remark code (RARC, such as N290 or M51) on the same line usually tells you exactly what to fix.

Every payment or denial comes back on an ERA (electronic remittance advice) or paper EOB with these codes. Reading them correctly is the difference between a fix that takes five minutes and a claim that sits until the filing deadline passes.

Group codes: who owes the amount

Group code	Meaning	Can you bill the patient?
CO	Contractual obligation	No. The provider absorbs it or fixes the claim.
PR	Patient responsibility	Yes: deductible, coinsurance, copay or non-covered services the patient agreed to.
OA	Other adjustment	Depends on the reason code. Often coordination of benefits.
PI	Payer-initiated reduction	No, unless the contract says otherwise.

The most common denial codes and their fixes

Code	What it means	Usual fix
CO-4	Procedure code inconsistent with the modifier, or a required modifier is missing	Add or correct the modifier (for example 95 for telehealth, 25 for a separate E/M) and resubmit
CO-11	Diagnosis inconsistent with the procedure	Check the diagnosis code and pointer against the note
CO-16	Claim lacks information or has billing errors	Read the RARC, add what is missing, send a corrected claim
CO-18	Exact duplicate claim or service	Check whether the original claim was paid or is pending before resending
CO-22	May be covered by another payer (coordination of benefits)	Confirm primary and secondary insurance with the patient, bill the right payer first
CO-27	Expenses incurred after coverage ended	Verify eligibility; find the patient’s new coverage
CO-29	Time limit for filing has expired	Appeal only with proof of timely submission (see our timely filing guide)
CO-45	Charge exceeds the fee schedule or contracted amount	Not a denial: write off the difference, but check the allowed amount matches your contract
CO-50	Not medically necessary, according to the payer	Check documentation and diagnosis; appeal with records if the service was necessary
CO-96	Non-covered charge	Check the benefit; bill the patient only if they agreed in advance
CO-97	Payment included in another service already adjudicated (bundling)	Check coding edits; add a modifier only if the services were truly separate
CO-109	Not covered by this payer; send to the correct payer	Find the right payer, often a behavioral health carve-out or Medicare Advantage plan
CO-119	Benefit maximum reached	Check visit limits; ask about exceptions or bill the patient if they agreed
CO-167	Diagnosis not covered	Review the diagnosis coding; some plans exclude certain diagnoses
CO-170	Payment denied when performed by this type of provider	Check that your license type is covered for this service by this plan
CO-185	Rendering provider not eligible to perform the service	Usually a credentialing or taxonomy problem; check enrollment
CO-197	Precertification or authorization absent	Resubmit with the authorization number, or request a retro authorization / appeal
CO-242	Services not provided by network providers	Check that you are in-network for this plan and network, not just the payer
PR-1	Deductible amount	Bill the patient
PR-2	Coinsurance amount	Bill the patient
PR-3	Copayment amount	Bill the patient (or it was collected at the visit)
PR-204	Service not covered under the patient’s current benefit plan	Bill the patient if they agreed in advance; otherwise review coverage

Denials that are really credentialing problems

In mental health billing, several denials that look like coding issues are actually credentialing issues:

• CO-109 or CO-242 often mean the plan’s behavioral health benefit is run by a different company, and you are in-network with the medical plan only.
• CO-185 or CO-170 often mean the clinician is not enrolled with that plan yet, is linked to the wrong group, or has the wrong taxonomy on file.

No amount of resubmitting fixes these. The fix is getting the credentialing right. See how to get paneled with insurance.

Corrected claim, reconsideration or appeal?

• Rejection (the claim never reached the payer’s system): fix and resubmit as a new claim.
• Denial caused by your error (wrong code, missing modifier): send a corrected claim (frequency code 7) or follow the payer’s correction process.
• Denial you disagree with (medical necessity, bundling, timely filing with proof): file a reconsideration or appeal with supporting records. See how to appeal a denied claim.

Stop the same denial from coming back

Fixing claims one by one is only half the job. Track denials by code, payer and provider every month, and fix the setting, form or habit that causes them. That is how our clients see an average 38% reduction in denials. If denials are piling up, our denial management team works every one within 5 business days, and a free claims audit shows where they come from.

Code definitions are published by the X12 code committees and are updated several times a year. Payers may use them differently, so read the remark codes and the payer’s policy for each claim.

Frequently asked questions