These codes appear on your Explanation of Benefits (EOB) or denial letter. Here is what they mean in plain English.
CO-4 - Missing or incorrect modifier
Your claim was missing a code that tells the insurer more detail about how or where a service was performed. Without it, the claim cannot be processed.
Ask your provider to review the claim for missing modifiers and resubmit with the correct modifier attached. This is a provider-side fix, not an appeal.
CO-11 - Diagnosis does not support the procedure
The insurer says the diagnosis code on your claim does not justify the procedure that was billed. This is often a coding mismatch, not a clinical judgment.
Request an itemized bill from your provider. Verify that the diagnosis and procedure codes are accurate. If correct, appeal with clinical documentation showing why the procedure was necessary for your diagnosis.
CO-15 - Prior authorization missing or invalid
High when clinical documentation is strongThe insurer required pre-approval for this service before it was performed, and that approval was either not obtained or is not showing correctly on the claim.
Check whether your provider obtained prior authorization. If they did, ask them to resubmit with the authorization number. If no auth was obtained, file an appeal with clinical documentation supporting medical necessity. Retroactive authorization is sometimes granted.
CO-16 - Missing information or submission error
Very high when corrected and resubmittedThe claim is incomplete. A required field -- patient ID, provider NPI, or supporting documentation -- is missing or incorrect.
This is almost always a provider billing error. Contact your provider's billing department and ask them to correct and resubmit the claim. You should not owe anything while this is being resolved.
The insurer has already received and processed this claim. A second submission was flagged as a duplicate.
Verify with your provider whether the original claim was paid. If it was, no action is needed. If it was not paid, ask your provider to appeal with documentation showing the original claim was not processed.
CO-29 - Claim filed after the deadline
Low -- deadlines are strictly enforcedYour provider submitted the claim after the insurer's filing deadline. Most insurers have strict windows -- typically 90 to 365 days from the date of service.
This is a provider-side error. Ask your provider to appeal with documentation showing why the filing was late. Some insurers grant exceptions for extenuating circumstances. Patients are generally not responsible for late filing penalties.
CO-45 - Charges exceed the allowed amount
Your provider billed more than what your insurer has agreed to pay for this service. If your provider is in-network, you cannot be billed for the difference. This is called balance billing and is generally prohibited for in-network providers.
If your provider is in-network, you owe only your plan's cost-sharing (copay, coinsurance, or deductible). You are not responsible for the difference between billed and allowed amounts. Contact your insurer if the provider attempts to bill you for the balance.
CO-50 - Medical necessity denied
High -- approximately 44% of internal appeals succeed industry-wideThe insurer decided the service was not medically necessary based on their coverage criteria. This is one of the most common and most frequently overturned denials.
Appeal with your doctor's clinical notes, test results, and a letter from your physician explaining why the service was necessary. Reference the insurer's specific medical necessity criteria in your appeal. CO-50 denials are among the most commonly overturned in external review.
CO-97 - Service bundled into another payment
The insurer says this service is already included in the payment for a different service that was billed at the same time. You cannot be paid separately for it.
Ask your provider to verify the bundling rules for these procedure codes. If the services were genuinely separate and distinct, your provider may be able to resubmit with a modifier indicating they should be billed separately.
CO-109 - Wrong payer billed
The claim was sent to the wrong insurance company. This is a billing error.
Contact your provider's billing department. Verify which insurer should be billed as primary. Ask them to resubmit to the correct payer.
PR-1 - Deductible applies
You have not yet met your annual deductible. You are responsible for this amount until your deductible is satisfied. This is not a denial -- it is how your plan works.
Verify your current deductible balance with your insurer. Track your deductible progress in your Bill Advantage claims ledger. Once your deductible is met, your plan begins sharing costs.
PR-2 - Coinsurance applies
You are responsible for your share of the cost after the deductible is met. Your plan covers a percentage and you owe the rest. This is not a denial.
Verify the coinsurance percentage in your Summary of Benefits and Coverage. Confirm the allowed amount was calculated correctly. If the amount seems wrong, contact your insurer.
You owe a fixed copay for this service. This is not a denial -- it is your plan's standard cost-sharing.
Verify the copay amount matches your plan documents. If you have already paid the copay, confirm with your provider that it was recorded.
610 - Charges exceed allowable amount (payer-specific)
This is a payer-specific code used by some insurers, including Wellmark Blue Cross Blue Shield, to indicate that billed charges exceed the allowable rate. If your provider is in-network, you are not responsible for the difference.
Confirm your provider is in-network. If they are, you owe only your plan cost-sharing, not the full billed amount. Contact your insurer if the provider attempts to collect the balance.
