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M88 Remark Code (Deactivated): Lab Must Bill Its Own Work

M88 meant the payer would not pay for laboratory tests unless the laboratory that performed them billed for them. X12 deactivated it and suggested reason code B20.

X12 deactivated RARCM88 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: M88 (RARC M88)
Status: Deactivated StoppedAugust 1, 2004 (in use since January 1, 1997).
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): The provider who billed a test it did not perform bore the denial.
Official description: We cannot pay for laboratory tests unless billed by the laboratory that did the work.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What M88 meant

Remark M88 addressed “pass-through” lab billing. A physician office or other provider had billed for lab tests that were actually run by another laboratory. The payer denied them because it pays only the lab that did the work.

What replaced it

X12’s note suggests reason code B20. CO-B20 says the service was partially or fully furnished by another provider. Related remarks include M12, which asks diagnostic claims to show whether purchased services are included, and N347 when payment already went to another provider for the same service.

If you still see M88

It only appears in older data. If your office receives similar denials today, review how lab orders flow: tests sent to a reference lab should normally be billed by that lab, and your claim should include only services your office performed. Check payer rules before billing any purchased lab service.

CO-B20 (Procedure/service was partially or fully furnished by another provider.): The suggested replacement: procedure or service partially or fully furnished by another provider.
M12 (Diagnostic tests performed by a physician must indicate whether purchased services are included on the claim.): Diagnostic tests performed by a physician must indicate whether purchased services are included.
N347 (Your claim for a referred or purchased service cannot be paid because payment has already been made for this same service to another provider by a…): Payment already made for this same referred or purchased service to another provider.

M88 FAQ

Why couldn't a physician bill for tests a reference lab performed?

Many payers, including Medicare in most cases, require the performing laboratory to bill for the tests it runs, with limited exceptions. The ordering office bills only for what it performs, such as specimen collection.

What should the ordering office do after this denial?

Stop billing the test and confirm the performing lab is billing the payer directly, unless the payer's rules allow a specific exception.

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