CO B23 denial code

Claim adjustment reason code B23. Often reported as CO B23.

Lab not authorized for this test (CLIA)

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What B23 means

The payer will not pay this lab test because the lab's CLIA standing, tied to its proficiency testing, does not authorize it.

Clinical labs are regulated under the Clinical Laboratory Improvement Amendments (CLIA), and the lab's CLIA standing, including its proficiency testing, limits which tests it may bill. B23 means the payer checked the test against that record and found the lab not authorized for it.

This is usually a lab data or certification issue, not a coverage question for the patient.

Group codes seen with B23

On a remittance, B23 comes after a group code. These are the ones it is most often reported with:

• CO B23 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The CLIA number was missing, invalid or not linked to the billing provider.
• The lab holds a waiver certificate but billed a test that needs a higher certification.
• The CLIA certificate had lapsed or did not yet include the test on the date of service.

What to do next

1. Verify the CLIA number on the claim matches the lab that performed the test.
2. Check the certificate type and effective dates against the test billed.
3. Add the correct CLIA number or required modifier and resubmit if the data was wrong.
4. Update the lab's certification before billing more tests at that complexity level.

Related codes

• B7 (reason code) Provider not certified for the service
• 16 (reason code) Missing information or billing error