CO-16 denial code
The claim is missing information the payer needs, or something on it is inconsistent. It is the most common denial there is, and on its own it tells you almost nothing — the useful detail is always in the remark codes sitting next to it.
CO — Contractual Obligation. The write-off is yours. You agreed to it in your contract with the payer, and you cannot bill the patient for it.
Why you got it
- 1A required field is blank or malformed: subscriber ID, date of birth, referring provider NPI, place of service.
- 2The diagnosis code is invalid, truncated, or was deleted in a previous code year.
- 3A code that requires a seventh character was submitted without one, so it is not a valid code at all.
- 4A non-billable header code (a category rather than a specific code) was submitted as if it were billable.
- 5Required documentation or an attachment the payer expected was not received.
How do I fix a CO-16 denial?
- Read the RARC codes on the same remittance line. CO-16 is a container; the remark code tells you what is actually missing.
- Check the diagnosis codes first — invalid and incomplete codes are the single most common cause, and they are also the easiest to verify.
- Correct the specific field and resubmit as a corrected claim. CO-16 is almost always correctable rather than appealable.
How to stop the next one
Most of the coding causes are detectable before submission. An incomplete code, a deleted code, or a header code billed as specific are all visible the moment the diagnosis set is checked.
We can catch the coding cause of this one before you submit
Paste the diagnosis codes into our free scrubber and it will flag the invalid, incomplete, and conflicting codes that produce CO-16 — quoting the CMS note behind each one. No signup.
Check a claim, freeIf denials like this are a volume problem rather than a one-off, the denial management page explains how the paid workspace catches the coding causes on every claim, and the free ICD-10-CM lookup shows the coding notes behind any diagnosis code on the remittance.