Digoxin Therapeutic Drug Assay — NCD 103 | CMS Coverage Update

TL;DR: The Centers for Medicare & Medicaid Services modified NCD 103 governing digoxin therapeutic drug assay coverage, with an effective date of March 7, 2026. Here's what billing teams need to know.

This update to the CMS digoxin therapeutic drug assay coverage policy tightens the clinical indications framework that determines when Medicare will pay for digoxin level testing. NCD 103 is the National Coverage Determination governing Medicare coverage of digoxin monitoring across cardiology, nephrology, internal medicine, and any practice managing patients on chronic digoxin therapy. The policy does not list specific CPT codes in this version — but digoxin therapeutic drug assay billing is directly affected by the medical necessity criteria outlined here. Get this wrong and you're looking at claim denial on a test your patients genuinely need.

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Quick-Reference Table

Field	Detail Copy
Payer	CMS (Centers for Medicare & Medicaid Services)
Policy	Digoxin Therapeutic Drug Assay
Policy Code	NCD 103
Change Type	Modified
Effective Date	2026-03-07
Impact Level	Medium
Specialties Affected	Cardiology, Nephrology, Internal Medicine, Gastroenterology, Endocrinology, Clinical Laboratory
Key Action	Audit your digoxin assay orders against the updated clinical indications list before billing claims on or after March 7, 2026.

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CMS Digoxin Therapeutic Drug Assay Coverage Criteria and Medical Necessity Requirements 2026

The core of NCD 103 hasn't changed in intent, but the modified version clarifies the clinical indications framework that supports medical necessity. If you're asking whether digoxin therapeutic drug assay testing is covered under Medicare, the answer is yes — but only when specific clinical conditions are documented in the medical record.

Who Qualifies: Patients Currently on Digoxin

Medicare covers digoxin level testing for patients actively receiving digoxin therapy. The clinical rationale is straightforward: digoxin has a narrow therapeutic index. Too little and it's ineffective. Too much and it's toxic. That window is tight enough that regular monitoring is clinically defensible — but CMS still requires documented justification.

The coverage policy recognizes these clinical indications for patients currently on digoxin:

Each of these needs to be documented in the chart — not just checked off. A coder seeing "digoxin level ordered" without clinical context is looking at a potential claim denial waiting to happen.

Steady-State Monitoring: The Gray Area

This is where the coverage policy gets complicated — and where your billing team needs to pay close attention.

CMS acknowledges that "the value of obtaining regular serum digoxin levels is uncertain." That's a direct quote from NCD 103. It's an unusual thing for a coverage policy to say, and it creates real documentation risk for routine monitoring orders.

CMS does allow annual testing after steady state is achieved. Steady state takes roughly one week in patients with normal renal function, and two to three weeks in patients with renal impairment. After that, annual testing is the baseline expectation — not monthly, not quarterly unless there's a documented clinical trigger.

Those triggers are specific. Medicare reimbursement for additional testing beyond the annual check requires documentation of at least one of these:

If none of those are present in the record and your provider is ordering digoxin levels every 90 days as routine protocol, you have a medical necessity problem. Talk to your compliance officer before the March 7, 2026 effective date if your practice currently runs high-frequency digoxin monitoring without trigger-based documentation.

Dosage Change Protocol

The policy is clear on one specific scenario: after a dosage change or the addition of a medication affecting digoxin levels, check the level one week after the change. That's a covered indication with a specific timing parameter. Document the change, document the timing, and your claim has a solid foundation.

In cases of confirmed or suspected digoxin toxicity, testing may be done more than once per week. That's an explicit carve-out in NCD 103 — but it requires toxicity to be documented as the clinical basis, not just elevated levels without clinical correlation.

Approved Diagnoses for Coverage

Digoxin is approved under this policy for three primary conditions:

#	Covered Indication Copy
1	Heart failure due to systolic dysfunction
2	Atrial fibrillation or flutter (for ventricular rate control)
3	Other supraventricular arrhythmias, particularly in the presence of heart failure

If your patient's diagnosis falls outside these, your medical necessity argument weakens significantly. Document the approved cardiac diagnosis clearly on every order.

The Prior Authorization Question

NCD 103 does not list prior authorization requirements for digoxin therapeutic drug assay testing. This is a national coverage determination — prior auth requirements at the Medicare Administrative Contractor (MAC) level may still apply in some regions. Check with your MAC before assuming blanket approval, especially for high-frequency testing scenarios.

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CMS Digoxin Therapeutic Drug Assay Exclusions and Non-Covered Indications

NCD 103 is explicit about two patient populations who do not qualify for this benefit. These exclusions are hard stops — not gray areas.

Patients on digitoxin — not digoxin — are excluded. Digitoxin is a different cardiac glycoside. The assay designed for digoxin monitoring doesn't apply, and Medicare will not reimburse for it under this policy code.

Patients treated with digoxin FAB (fragment antigen binding) antibody — the antidote used in severe digoxin toxicity — are also excluded. The clinical reason is logical: FAB antibody therapy binds digoxin and makes serum levels unreliable and clinically uninterpretable. Billing for a test that can't produce actionable results is a medical necessity failure, not just a coverage technicality.

Document the patient's current medications clearly. If FAB antibody therapy is in the record, digoxin assay billing stops until the clinical picture changes.

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Coverage Indications at a Glance

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CMS Digoxin Therapeutic Drug Assay Billing Guidelines and Action Items 2026

Here's what your billing team and clinical staff need to do before and after March 7, 2026.

Copy Action Items

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CPT, HCPCS, and ICD-10 Codes for Digoxin Therapeutic Drug Assay Under NCD 103

Specific Codes Listed in Policy Data

The policy data for NCD 103 does not include specific CPT, HCPCS, or ICD-10 codes in this version. CMS references quarterly Covered Code Lists — updated on a quarterly basis — as the authoritative source for applicable codes under this NCD.

What this means for your billing team: Do not assume a single code applies here without checking the current quarterly Covered Code List. CMS maintains these lists separately from the NCD narrative, and they are updated independently. Your billing guidelines should reference the current quarter's list, not a static code pulled from an older version of the policy.

Check the current Covered Code List at the CMS source for NCD 103, and cross-reference with the Medicare Claims Processing Manual, Chapter 120 — Clinical Laboratory Services Based on Negotiated Rulemaking — for claims processing instructions.

ICD-10 Diagnosis Codes to Support Medical Necessity

No ICD-10 codes are specified in the NCD 103 policy data. However, your claim documentation should reflect the approved indications. Work with your coding team to identify the ICD-10-CM codes that map to the approved diagnoses — heart failure with systolic dysfunction, atrial fibrillation, atrial flutter, and other supraventricular arrhythmias — and to the clinical triggers documented in the record. Your MAC may have published specific ICD-10 guidance in a related local coverage determination.

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