ABN in Clinical Trial Billing (CMS-R-131)

An Advance Beneficiary Notice of Noncoverage (ABN), CMS Form CMS-R-131, is the standard written notice a Medicare provider gives a fee-for-service Medicare beneficiary before furnishing an item or service the provider has reason to believe Medicare will not pay for. In ordinary outpatient billing this is a routine, largely mechanical form. In clinical trial billing it does real work: it is one of the few tools available for shifting financial responsibility to the patient when a specific item tied to trial participation falls outside what Medicare’s routine-costs coverage actually covers — and, just as importantly, it is a tool with sharp limits that research billing staff need to understand before relying on it.

This guide explains what the ABN is for, exactly when it applies inside a clinical trial billing workflow, and — because this is where research administrators most often go wrong — what it cannot be used for. It builds directly on CASRAI’s existing coverage of Medicare Clinical Trial Policy (NCD 310.1) and the Clinical Trial Billing Compliance checklist; read this guide as the detail page for one specific piece of that larger workflow, not a replacement for it.

Where the ABN fits relative to NCD 310.1

CMS National Coverage Determination (NCD) 310.1 is what makes the “routine costs” of a qualifying clinical trial payable by Medicare in the first place — the standard-of-care visits, scans, and management a beneficiary would have received regardless of trial participation. The Medicare Coverage Analysis (MCA) process exists to sort every protocol item into one of three buckets before the trial opens: routine costs (Medicare/insurer-billable), research costs (sponsor-billable), and ordinary patient responsibility (copay/coinsurance/deductible). See the Clinical Trial Billing Compliance checklist for that full three-way split.

The ABN sits downstream of that classification, not inside it. It doesn’t change which bucket an item belongs to — it’s the mechanism a provider uses when a specific routine-cost item, or an item in a non-qualifying trial, might not actually get paid by Medicare for a reason unrelated to the trial’s coverage status: medical necessity, frequency limits, or a statutory exclusion that would apply whether or not a trial were involved.

When an ABN actually applies in clinical trial billing

Three fact patterns account for most legitimate ABN use in a trial context:

1. The trial itself does not meet NCD 310.1’s qualifying criteria

If a study doesn’t meet NCD 310.1’s qualifying-trial test — see Medicare Clinical Trial Policy (NCD 310.1) for the full criteria — then none of its routine costs get the trial-specific coverage pathway, and ordinary Medicare coverage rules apply to each item on its own merits. Where a specific item would be denied under those ordinary rules, standard ABN practice applies exactly as it would for any non-trial service.

2. A specific routine-cost item is expected to be denied for medical necessity or frequency reasons

Even inside a qualifying trial, an individual routine-cost item can still be denied on grounds that have nothing to do with the trial — for example, a scan ordered more frequently than Medicare’s local coverage policy allows, or a service the treating physician can’t document as medically necessary for this particular beneficiary. Trial participation doesn’t immunize a routine-cost item from the ordinary medical-necessity and frequency edits a Medicare Administrative Contractor (MAC) applies to any claim.

3. An investigational item or device carries a statutory (not trial-related) exclusion

Some items are excluded from Medicare coverage by statute regardless of trial context — for instance, an investigational device that hasn’t met the applicable coverage criteria for its device category. Where the exclusion is statutory rather than a medical-necessity judgment call, an ABN is voluntary rather than mandatory (see the modifier discussion below), but issuing one is still good practice: it documents that the beneficiary understood the financial exposure before the item was furnished.

What the ABN cannot do: it is not a way to shift sponsor-owed research costs to the patient

This is the single most important limit for research billing staff to internalize, and it’s a genuine risk area rather than a technicality. Research costs — the investigational drug or device itself, and protocol-mandated visits or tests that exist only because the study requires them — are the sponsor’s contractual responsibility under the clinical trial agreement (CTA), not Medicare’s and not the patient’s. An ABN cannot lawfully convert a sponsor-owed research cost into patient financial responsibility just because Medicare (correctly) won’t pay for it; Medicare was never supposed to be billed for it in the first place. Using an ABN this way doesn’t just fail to protect the provider — it can compound the exact double-billing/miscategorization fact pattern that drives clinical-trial-billing False Claims Act exposure. See False Claims Act Liability in Clinical Trial Billing for how billing errors of this kind have led to real enforcement action. The correct fix for a research-cost item is to route it through the sponsor per the CTA budget and the trial’s coverage analysis, not to issue an ABN to the patient.

Mandatory use, voluntary use, and the ban on blanket ABNs

CMS distinguishes mandatory from voluntary ABN use. Mandatory use applies when a provider expects Medicare to deny an otherwise-covered item or service for a beneficiary-specific reason — typically medical necessity or a frequency limitation — and wants the option to bill the beneficiary if that denial occurs. Voluntary use applies to items and services Medicare never covers at all (statutorily excluded), where giving notice isn’t required to bill the patient but is still considered good notice practice.

What CMS guidance consistently prohibits, in either case, is issuing ABNs routinely or as a blanket practice — for example, giving every enrolled trial participant a standing ABN at enrollment “just in case.” An ABN has to be tied to a specific item or service and a specific, defensible reason to expect denial for that beneficiary; a blanket notice given without an individualized reason doesn’t meet CMS’s requirement and doesn’t reliably protect the provider’s ability to bill the patient later.

The three notice options a beneficiary chooses from

The CMS-R-131 form presents the beneficiary with three options, and the beneficiary — not the provider — selects one before the item or service is furnished:

Option 1 — the beneficiary wants the item or service, authorizes the provider to bill Medicare, and understands they are responsible for payment if Medicare denies the claim.
Option 2 — the beneficiary wants the item or service but asks that it not be billed to Medicare at all, and agrees to pay for it directly.
Option 3 — the beneficiary does not want the item or service; it is not furnished and not billed.

Only a beneficiary who selects Option 1 generates a claim with appeal rights attached if Medicare denies it — which is part of why the choice, and the documentation of it, matters.

Delivery and timing requirements

An ABN has to be delivered far enough in advance of the item or service being furnished that the beneficiary has real time to consider the options and ask questions — it cannot be presented at the point of service as a formality, and it cannot be given after the item has already been furnished. It must be in writing, on the current CMS-R-131 form (or an approved electronic equivalent), and completed with the specific item/service and the specific reason denial is expected — generic or vague reasons don’t satisfy the requirement. A properly executed, unmodified ABN is generally treated as valid for up to one year for a repeated course of treatment, provided the underlying circumstances (item, frequency, reason for expected denial) haven’t changed; a change in any of those requires a new notice.

How ABN status connects to the claim: the GA, GZ, GX, and GY modifiers

Whether and how an ABN was issued determines which HCPCS modifier goes on the claim line, and MACs process claims differently depending on which one is used:

GA — a mandatory ABN was issued for an item expected to be denied as not reasonable and necessary; if Medicare denies the claim, financial liability shifts to the beneficiary.
GZ — the item is expected to be denied as not reasonable and necessary, but no ABN was issued; the provider cannot bill the beneficiary if Medicare denies the claim, and liability stays with the provider.
GX — a voluntary ABN was issued for an item that is statutorily excluded from Medicare coverage (or otherwise not a Medicare benefit).
GY — the item is statutorily excluded from Medicare coverage (or doesn’t meet the definition of a Medicare benefit); no ABN is required.

These are distinct from — and reported alongside, not instead of — the trial-specific claim flags covered in CASRAI’s Condition Code 30 reference (institutional Condition Code 30, the Z00.6 diagnosis code, the NCT number, and the outpatient Q0/Q1 modifiers). Condition Code 30 and Q0/Q1 identify a claim or line item as trial-related; GA/GZ/GX/GY separately describe the ABN and liability status of a given line. A single claim line for a trial-related item can legitimately carry both kinds of flag at once.

What happens if a required ABN isn’t issued

If a provider expected a medical-necessity or frequency-based denial, didn’t issue an ABN, and the claim is then denied, the GZ modifier applies and the provider cannot bill the beneficiary for that item — the financial exposure stays with the provider, not the patient. In a trial context this is a real operational risk: a coverage analysis that correctly identifies a routine-cost item, but doesn’t flag that the item also carries a plausible reason for denial on ordinary Medicare grounds, can result in an unbillable claim discovered only after the service has already been furnished.

Building ABN triggers into the coverage analysis

Because the ABN decision is made before the item is furnished, it has to be anticipated during the Medicare Coverage Analysis, not improvised at the billing-office level after the fact. Practices that keep ABN issuance reliable typically build it into the same billing grid used for the routine-cost/research-cost split: for every routine-cost item, the grid notes not just which payer is billed but whether that item carries a known frequency limit, a local coverage determination with medical-necessity criteria, or another basis on which a MAC has previously denied it — and flags those items for ABN issuance before the corresponding visit. This keeps the ABN decision tied to the coverage analysis that already governs the rest of the trial’s billing, rather than treated as a separate, ad hoc judgment call by front-line staff.

Frequently asked questions

Does Medicare require an ABN for every item in a clinical trial?

No. Most routine-cost items in a qualifying trial are covered under NCD 310.1 the same way they would be outside a trial, and don’t need an ABN at all. An ABN is only relevant for a specific item where a provider has a genuine, individualized reason to expect denial — medical necessity, a frequency limit, a statutory exclusion, or (for a non-qualifying trial) the loss of the trial-specific coverage pathway entirely.

Can an ABN be used to bill a patient for the investigational drug or device itself?

No. The investigational product and other sponsor-owed research costs are the sponsor’s responsibility under the clinical trial agreement, not the patient’s. An ABN addresses Medicare coverage denial for items that would otherwise be billed to Medicare — it has no legitimate role in shifting a cost that was never supposed to reach Medicare or the patient in the first place. See False Claims Act Liability in Clinical Trial Billing.

Is a blanket ABN given to every trial participant at enrollment valid?

No. CMS guidance requires an ABN to be tied to a specific item or service and a specific, defensible reason to expect denial for that particular beneficiary. A standing notice issued to every enrollee regardless of what’s actually being furnished doesn’t meet that requirement.

What’s the difference between the GZ and GY modifiers?

GZ is used when a denial is expected on medical-necessity or frequency grounds and no ABN was issued — the provider cannot then bill the beneficiary. GY is used for items that are statutorily excluded from Medicare coverage altogether, where an ABN was never required in the first place.

Where does ABN issuance fit relative to the Medicare Coverage Analysis?

It should be planned during the MCA, not decided at the point of service. Items with a known frequency limit or medical-necessity risk should be flagged in the billing grid so front-line staff know in advance which visits require an ABN conversation with the beneficiary.

Advance Beneficiary Notice (ABN) in Clinical Trial Billing: When Medicare Won’t Cover Routine Costs