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N721 Remark Code: Covered Only in a Clinical Trial

N721 means the payer covers this service only when it is provided as part of a clinical trial. Either the patient was not in a qualifying trial, or the claim did not carry the information that identifies trial participation.

Code: N721 (RARC N721)
Status: Active In use since March 1, 2014.
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): The provider absorbs the denial, usually because trial status was not reported or the coverage rule was not met.
PR (Patient Responsibility): The payer places the cost on the patient, which may be possible if the patient was properly informed in advance. Check plan rules and any required notice.
Official description: This service is only covered when performed as part of a clinical trial.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What N721 means

N721 marks a service the payer will fund only inside a clinical research setting. Outside that setting, the payer treats it as non-covered. The remark usually accompanies CARC 96, CARC 272, or CARC 55.

It shows up in two different situations, and it matters which one you are in:

The patient was enrolled in a qualifying trial, but the claim did not include the identifiers the payer uses to recognize trial claims.
The patient was not in a trial, so the coverage condition was simply not met.

Common causes

Trial modifiers, registry number, or trial diagnosis were left off the claim.
The study was not one the payer recognizes as qualifying.
Research billing and standard billing were not separated, so a trial-covered service went out as routine care.
The service was performed before enrollment or after the patient left the study.

How to fix it

Confirm with the research team whether the patient was enrolled on the date of service and in which study.
If enrolled, add the payer’s required trial identifiers and send a corrected claim with resubmission code 7 and the original claim number.
If the payer does not recognize the study, ask what qualification it requires and whether an appeal with study documentation is appropriate.
If the patient was not in a trial, the service may not be payable. Review whether any advance notice given to the patient allows billing them.

How to prevent it

Flag research participants in registration so their claims route through research billing review. Keep a current list of each payer’s clinical trial coding requirements, since they differ.

Codes that may appear with N721

CO-96 (Non-covered charge(s).): The charge is non-covered outside a trial.
CO-272 (Coverage/program guidelines were not met.): The coverage guideline tying payment to trial participation was not met.
CO-55 (Procedure/treatment/drug is deemed experimental/investigational by the payer.): The payer considers the service investigational outside a trial setting.

N789 (Clinical Trial is not a covered benefit.): The opposite direction: clinical trial care is not a covered benefit under this plan.
MA50 (Missing/incomplete/invalid Investigational Device Exemption number or Clinical Trial number.): The investigational device exemption or clinical trial number was missing or invalid.
MA97 (Missing/incomplete/invalid Medicare Managed Care Demonstration contract number or clinical trial registry number.): The clinical trial registry number was missing or invalid.

N721 FAQ

Why would a payer cover something only in a trial?

Some payers cover emerging treatments only under coverage with evidence development, where data is collected in an approved study. Outside the study, the same service is treated as not covered.

How do I show the service was part of a trial?

Payers differ. Medicare, for example, uses trial-related modifiers such as Q0 and Q1, a trial registry number, and the diagnosis Z00.6 in certain cases. Other payers publish their own requirements.

What if the patient really was in the trial?

Correct the claim so it carries the payer's trial identifiers and resubmit as a corrected claim, or appeal with enrollment documentation if the claim was already coded correctly.

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