CO-16 Denial Code: Missing Information / Billing Error

The official definition

“Claim/service lacks information or has submission/billing error(s)”

That is the verbatim definition of CARC 16 from the X12 Claim Adjustment Reason Code set, the standardized codes every insurer uses on EOBs and remittance advices. The letters in front of the number are the group code. CO: Contractual Obligation: an adjustment between the provider and the insurer. An in-network provider should not bill you for CO amounts.

What it means in plain English

Something required was missing from the claim or entered incorrectly: a provider ID, a date of birth, a place-of-service code, a diagnosis code. This is the most general administrative denial there is, and the accompanying remark code (RARC) tells you exactly what was missing. It says nothing about whether your care was covered. The paperwork just failed.

What to check on your EOB

• The RARC (remark) code on the EOB. It names the specific missing or invalid item.
• Your own information on the claim: name, date of birth, member ID. A single transposed digit can trigger this denial.
• Whether the provider has your current insurance card on file.

What to do next

1. Call the provider's billing office with the RARC code and ask them to correct and resubmit the claim.
2. Do not pay a bill generated by this denial. A corrected resubmission usually resolves it entirely.
3. Follow up in 30 days to confirm the corrected claim was actually resubmitted.

Who's responsible

Provider. Most denials carry a clear owner. Knowing whether the fix belongs to you, your doctor, or the billing office is half the battle. If it's the provider's error, you should not be paying for it.

Want the fundamentals first? Start with how to read an EOB and the 7 most common billing errors. This page is general information about standardized denial codes, not legal or medical advice.