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CO-B12 Denial Code: Service Not Documented in Records

CO-B12 means the payer reviewed the medical record and found no documentation that the billed service was performed. Without documentation, the payer treats the service as not rendered for billing purposes and denies or recoups payment.

Quick facts

Code
CO-B12 (CARC B12)
Status
Active In use since January 1, 1995; last modified March 1, 2018.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The standard group. The provider is responsible and can't bill the patient for undocumented services.
Official description
Services not documented in patient's medical records.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-B12 means

CARC B12 says services not documented in the patient’s medical records. A payer can only pay for services the record supports. When it reviews the chart and can’t find the billed service, it denies the line or recovers the payment with CO-B12.

This code usually follows a review. The payer requested records, whether before paying (prepayment review) or afterward (post-payment audit), and compared them with the claim. “Not documented” can mean the note is missing entirely, lacks a required signature, or doesn’t mention the specific service billed.

Common causes

  • Records sent were incomplete, such as an office note without the procedure note, or a missing addendum.
  • Unsigned or unauthenticated notes, which payers may not accept as documentation.
  • Charges entered from a schedule or superbill for services that weren’t actually performed.
  • Services performed by staff but not recorded, for example injections or tests.
  • Wrong date of service, so the record for the billed date doesn’t show the service.
  • Time-based services without time documented.

How to fix it

  1. Pull the full record for the date of service, including procedure notes, orders, results, and addenda.
  2. Confirm the service was performed and documented. Check signatures and dates.
  3. If documentation exists, appeal with the complete, signed record and a cover letter pointing to where the service is documented.
  4. If the date was wrong, send a corrected claim with resubmission code 7 in box 22.
  5. If the service wasn’t documented or wasn’t performed, accept the denial and don’t bill the patient.
  6. Respond to records requests on time to avoid denials for non-response.

How to prevent it

  • Bill from documentation, not schedules. Charges should be tied to signed notes.
  • Require signatures before claims go out.
  • Audit a sample of charges against records regularly.
  • Train staff to document every service they perform, including injections and tests.
  • Track payer records requests so complete packets go out on time. See preventable medical claim denials.

Specialty notes

Behavioral health practices face CO-B12 when session notes lack start and stop times for time-based services. PT/OT practices see it when treatment notes don’t list each billed modality and its time.

Remark codes that may appear with CO-B12

  • M127 (Missing patient medical record for this service.): The patient's medical record for this service is missing.
  • N237 (Incomplete/invalid patient medical record for this service.): The medical record sent was incomplete or invalid.
  • N163 (Medical record does not support code billed per the code definition.): The record doesn't support the code billed per the code's definition.
  • N706 (Missing documentation.): Documentation is missing.
  • CO-112 (Service not furnished directly to the patient and/or not documented.): Service not furnished directly to the patient and/or not documented.
  • CO-150 (Payer deems the information submitted does not support this level of service.): Documentation doesn't support the level of service billed, rather than the service itself.
  • CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): Documentation is required to adjudicate the claim, usually before a decision is made.
  • CO-251 (The attachment/other documentation that was received was incomplete or deficient.): The documentation received was incomplete or deficient.

CO-B12 FAQ

When does CO-B12 usually appear?

After a records request, prepayment review, or post-payment audit. The payer compared what was billed with what was documented and found the service missing from the record.

Can I add documentation after the fact?

Only through a properly dated and identified late entry or addendum, made for accuracy and not just to support a claim. Altering or backdating records is not acceptable and can create serious compliance problems.

How do I appeal CO-B12?

Send the complete, signed record for the date of service, including any pieces missing from the original submission, such as procedure notes, orders, test results, or time logs.

Should I refund payments if the service wasn't documented?

If you confirm the service wasn't documented or wasn't performed, accept the denial or recoupment and review your processes. Consult your compliance guidance on reporting and refunds.