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. Curious what your denial rate actually costs? Run your numbers through the free Denial Cost Calculator. 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.