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M34 Remark Code (Deactivated): CLIA Number Missing

M34 meant the claim did not include the laboratory's CLIA certification number. X12 deactivated it and suggested MA120, which covers missing, incomplete, or invalid CLIA numbers.

X12 deactivated RARCM34 on August 1, 2004. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: M34 (RARC M34)
Status: Deactivated StoppedAugust 1, 2004 (in use since January 1, 1997).
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): Typically sent with CARC 16 under CO; the lab or practice needed to add the CLIA number.
Official description: Claim lacks the CLIA certification number.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What M34 meant

Labs and physician offices that run tests must be certified under CLIA, and payers commonly require the certification number on lab claims. Remark M34 explained a denial where that number simply was not on the claim.

What replaced it

X12’s note recommended MA120. MA120 is broader, covering CLIA numbers that are missing, incomplete, or invalid, and it is still active. It usually accompanies CO-16. When the number is valid but the lab’s certification does not allow the test, payers use CARC CO-B23.

If you still see M34

It belongs to older remittances. For a current CLIA problem, confirm the CLIA number on file for the location where the test was performed, add it in the claim field the payer requires, and resubmit. If you have several testing sites, make sure each claim carries the number for the site that ran the test.

MA120 (Missing/incomplete/invalid CLIA certification number.): The suggested replacement: missing, incomplete, or invalid CLIA certification number.
CO-B23 (Procedure billed is not authorized per your Clinical Laboratory Improvement Amendment (CLIA) proficiency test.): Procedure not authorized per the CLIA proficiency test.
CO-16 (Claim/service lacks information or has submission/billing error(s).): The adjustment code usually paired with CLIA-number remarks.

M34 FAQ

What is a CLIA number?

An identifier for a laboratory certified under the Clinical Laboratory Improvement Amendments. Many payers require it on claims for lab tests, including tests performed in physician offices.

What if the CLIA number is present but the test is still denied?

The certificate may not cover that level of test. For example, a certificate of waiver allows only waived tests. Check the certificate type against the tests billed.

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