A handful of denial codes account for the bulk of the rework that drains a practice's revenue cycle. Learn to recognize these on sight — what each means, and the single fastest way to resolve it — and you have already handled most of your denials. Each one below links to a full guide with causes, prevention, and a copy-ready appeal letter.
Every line below shows a group code (who owes the money) plus a CARC (the reason). CO means a contractual write-off you cannot bill the patient; PR means patient responsibility. Now, the list.
CO-45 Charge exceeds the allowed amount
The routine contractual difference between your billed charge and the payer's allowed amount — usually not a true denial at all. Confirm the allowed amount matches your contracted rate; only pursue it if the payer mispriced the claim. Full guidance →
CO-16 Claim lacks information
A catch-all for missing or invalid data. The real instruction rides in the RARC remark code next to it — read that, fix the flagged field, and resubmit a corrected claim rather than appealing. Full guidance →
CO-97 Bundled into another procedure
The service was rolled into another payment, usually by a National Correct Coding Initiative (NCCI) edit. If your documentation supports a separate, distinct service, append the right modifier (59 or an X{EPSU} modifier) and appeal. Full guidance →
PR-204 Not covered under the plan
The item isn't a benefit under the patient's plan, so it becomes patient responsibility. Re-verify eligibility; if you billed the wrong plan, correct it and resubmit to the right payer. Full guidance →
CO-50 Not medically necessary
The diagnosis doesn't meet the payer's coverage policy (an LCD or NCD for Medicare). These are frequently overturned — appeal with the diagnosis and chart notes that establish necessity, citing the policy's covered indications. Full guidance →
Got a remittance full of codes?
Paste an 835 or a list of codes into our free Denial Code Decoder and it decodes every line at once — meaning, fix, and appeal options for each. It runs entirely in your browser, so nothing you paste is ever uploaded.
Open the Denial Code Lookup & DecoderThe best denial is no denial
Notice how many of these — CO-97, CO-50, and CO-16 — trace back to a coding or documentation decision made before the claim ever left the building. That's the cheapest denial to work: the one you prevent. Medmio CodeSightTM reviews coding against payer rules at the point of charge capture, so coding-driven denials get caught before submission instead of worked weeks later. See how CodeSight works →
Educational guidance only, provided as-is with no guarantee of accuracy or outcome — not a substitute for professional billing, coding, or legal advice. The CARC and RARC code sets are maintained by X12 and CMS and change up to three times a year; verify against your payer contracts and the current code lists. For official Medicare guidance, see CMS.