TL;DR: The Centers for Medicare & Medicaid Services modified NCD 103, the national coverage determination governing digoxin therapeutic drug assay testing, effective March 7, 2026. Here's what billing teams need to know about CMS digoxin therapeutic drug assay coverage policy and when claims will — and won't — get paid.
CMS digoxin therapeutic drug assay coverage policy under NCD 103 draws a clear line between clinically justified monitoring and routine testing. The policy does not list specific CPT or HCPCS codes in its current version, which creates a documentation burden your billing team needs to address now. If your practice manages heart failure or atrial fibrillation patients on digoxin, this modification touches your revenue cycle directly.
Quick-Reference Table
| Field | Detail |
|---|---|
| Payer | CMS (Centers for Medicare & Medicaid Services) |
| Policy | Digoxin Therapeutic Drug Assay — NCD 103 |
| Policy Code | NCD 103 |
| Change Type | Modified |
| Effective Date | 2026-03-07 |
| Impact Level | Medium |
| Specialties Affected | Cardiology, Internal Medicine, Nephrology, Clinical Laboratory |
| Key Action | Audit documentation for all digoxin monitoring claims to confirm clinical indications align with NCD 103 criteria before submitting |
CMS Digoxin Therapeutic Drug Assay Coverage Criteria and Medical Necessity Requirements 2026
NCD 103 is the National Coverage Determination governing Medicare coverage of digoxin therapeutic drug assay testing. The policy exists because digoxin has a narrow therapeutic index — too little, and it doesn't work; too much, and it becomes toxic. That margin is exactly why medical necessity documentation matters more here than it does for most lab tests.
CMS covers digoxin level testing when a patient is on digoxin therapy and a specific clinical trigger is present. The coverage policy is not a blank check for routine monitoring. You need a documented reason for each test, and that reason must fit one of the defined indications.
Covered Clinical Indications — Patients Currently on Digoxin
CMS recognizes the following as valid medical necessity triggers for patients already receiving digoxin therapy:
| # | Covered Indication |
|---|---|
| 1 | Symptoms, signs, or ECG findings suggestive of digoxin toxicity. Nausea, bradycardia, visual disturbances, or ECG changes all qualify. Document the specific symptom or finding in the chart note. |
| 2 | Concurrent medications that affect digoxin pharmacokinetics. Drugs that change absorption, bioavailability, distribution, or elimination of digoxin — think amiodarone, clarithromycin, or verapamil — justify a level check. Name the interacting drug in the documentation. |
| 3 | Impaired renal, hepatic, gastrointestinal, or thyroid function. Digoxin is renally cleared. Patients with CKD accumulate it faster. CMS recognizes this. Document the organ impairment and its relevance. |
| 4 | pH and electrolyte abnormalities. Hypokalemia, hypomagnesemia, and acid-base disorders all shift digoxin's therapeutic window. Document the lab values that prompted the test. |
| 5 | Unstable cardiovascular status, including myocarditis. Document the clinical instability clearly. |
| 6 | Patient compliance monitoring. This is explicitly covered, but the chart needs to reflect a compliance concern — not just a standing order. |
Covered Clinical Indications — Special Circumstances
Two additional categories apply regardless of whether active digoxin therapy is confirmed:
| # | Covered Indication |
|---|---|
| 1 | Suspected accidental or intentional overdose. CMS covers testing here. Frequency can exceed once per week when clinical toxicity is actively being managed. |
| 2 | Patients with an acceptable cardiac diagnosis where an accurate digoxin use history is unobtainable. This covers situations like altered mental status, unconscious patients, or unreliable historians. Document why the history is unobtainable. |
Steady-State Monitoring — The Gray Area
This is where claims most often run into trouble. CMS acknowledges that regular serum digoxin levels have uncertain value. The policy language is deliberate: it says testing "may be reasonable" once yearly after steady state is achieved — not that it's automatically covered.
Steady state takes approximately one week in patients with normal renal function. In patients with renal impairment, plan for two to three weeks. After a dose change or the addition of an interacting medication, checking the level one week later is considered reasonable.
The real issue here is that "may be reasonable" is not the same as "covered." For annual steady-state checks, your documentation needs to show why a level was clinically indicated at that specific point in time — not just that the patient is on digoxin. A note that says "stable patient, routine digoxin level" is a claim denial waiting to happen.
If you're not sure how your MAC interprets this for annual monitoring claims, check for a local coverage determination that supplements NCD 103. Some Medicare Administrative Contractors have issued LCDs with additional frequency and documentation guidance. Your MAC's website is the starting point.
CMS Digoxin Therapeutic Drug Assay Exclusions and Non-Covered Indications
CMS is explicit about two exclusion categories. Both are hard stops — no amount of documentation makes these claims payable under NCD 103.
Patients on digitoxin. Digitoxin is a different cardiac glycoside. The assay for digoxin does not apply. Bill a different test with appropriate coding if digitoxin monitoring is indicated.
Patients treated with digoxin FAB (fragment antigen binding) antibody. Digibind and DigiFab are used to treat severe digoxin toxicity. Once a patient has received FAB antibody therapy, digoxin levels are unreliable and the standard assay is not appropriate. CMS excludes coverage in this setting. Document the FAB administration in the chart — and don't submit a digoxin level claim for this patient.
These are clean exclusions. Train your front-end billing staff to screen for both when verifying orders.
Coverage Indications at a Glance
| Indication | Status | Relevant Codes | Notes |
|---|---|---|---|
| Symptoms, signs, or ECG suggestive of digoxin toxicity | Covered | No specific codes listed in NCD 103 | Document specific symptom or ECG finding |
| Interacting medications affecting digoxin pharmacokinetics | Covered | No specific codes listed in NCD 103 | Name the interacting drug in chart documentation |
| Impaired renal, hepatic, GI, or thyroid function | Covered | No specific codes listed in NCD 103 | Document organ impairment and clinical relevance |
| pH or electrolyte abnormalities | Covered | No specific codes listed in NCD 103 | Include lab values that prompted the test |
| Unstable cardiovascular status, including myocarditis | Covered | No specific codes listed in NCD 103 | Document clinical instability clearly |
| Compliance monitoring | Covered | No specific codes listed in NCD 103 | Chart must reflect a specific compliance concern |
| Suspected accidental or intentional overdose | Covered | No specific codes listed in NCD 103 | May be tested more than once per week in toxicity cases |
| Acceptable cardiac diagnosis, digoxin history unobtainable | Covered | No specific codes listed in NCD 103 | Document why history is unobtainable |
| Annual steady-state level (stable patient) | Conditionally covered | No specific codes listed in NCD 103 | "Routine" alone is insufficient — needs a clinical trigger |
| Post-dose change or new interacting drug (one week after) | Conditionally covered | No specific codes listed in NCD 103 | Document the specific change and timing |
| Patients on digitoxin | Not Covered | — | Different drug; digoxin assay does not apply |
| Patients treated with digoxin FAB antibody | Not Covered | — | Assay unreliable after FAB therapy; hard exclusion |
CMS Digoxin Therapeutic Drug Assay Billing Guidelines and Action Items 2026
The effective date of March 7, 2026 is already here. If your team hasn't reviewed workflows against the updated NCD 103 criteria, start now.
| # | Action Item |
|---|---|
| 1 | Audit your standing orders for digoxin levels. Pull all active standing orders for digoxin monitoring across your cardiology, nephrology, and internal medicine panels. Flag any that lack a documented clinical trigger. A standing order without an indication tied to a current clinical status is a claim denial risk under this coverage policy. |
| 2 | Check for a MAC-level LCD that supplements NCD 103. NCD 103 sets the floor. Your Medicare Administrative Contractor may have issued a local coverage determination with more specific frequency limits, diagnosis code requirements, or documentation standards. Look up your MAC and search for digoxin-related policies before billing. |
| 3 | Update your documentation templates. Physicians and mid-levels ordering digoxin levels should be prompted to document the specific clinical trigger at the time of the order — not added as an afterthought. Build the indication into your EHR order workflow. "Digoxin level — indication: new amiodarone started 7 days ago" is defensible. "Digoxin level" alone is not. |
| 4 | Train staff on the two hard exclusions. Anyone touching cardiology or toxicology claims needs to know that digitoxin patients and post-FAB antibody patients are excluded from coverage under NCD 103. Add a claim-level screening step to your pre-bill review for these patient populations. |
| 5 | Clarify reimbursement expectations for annual steady-state monitoring. The "once yearly may be reasonable" language in NCD 103 does not guarantee reimbursement. Prepare your clinical team for the possibility that annual levels on stable patients without a new clinical trigger will face scrutiny. If you're billing annual levels routinely, talk to your compliance officer about your documentation practices before the next audit cycle. |
| 6 | Confirm prior authorization requirements with your MAC. NCD 103 does not specify a prior authorization requirement for digoxin assay testing. But some Medicare Advantage plans and supplemental MAC policies may have added one. Verify with your payer contacts before assuming it's a clean-submit service. |
| 7 | For toxicity cases, document frequency justification explicitly. CMS allows testing more than once per week during active toxicity management. But "more than once" requires clinical documentation that each test was necessary. Don't let frequency alone trigger a post-payment review — build the narrative into the chart note for each test. |
| Previous Version | Current Version |
|---|---|
| Coverage is considered experimental and investigational for all indications | Coverage is considered medically necessary when specific criteria are met |
| Prior authorization is not required | Prior authorization is required for initial treatment |
| Documentation must include clinical history | Documentation must include clinical history |
| Re-review every 24 months | Re-review every 12 months with updated clinical documentation |
CPT, HCPCS, and ICD-10 Codes for Digoxin Therapeutic Drug Assay Under NCD 103
Covered CPT Codes (When Selection Criteria Are Met)
The updated NCD 103 policy document does not list specific CPT or HCPCS codes. CMS references the quarterly Covered Code Lists published separately, which include narrative descriptions for applicable codes. Check the current Covered Code List on the CMS website to confirm which codes fall under NCD 103 for digoxin assay billing. Do not assume a code is covered or excluded based on this policy alone — verify against the current quarterly list.
For clinical laboratory billing teams, the absence of explicit codes in the NCD itself is not unusual. The cross-reference to the Claims Processing Manual, Chapter 120, Clinical Laboratory Services Based on Negotiated Rulemaking, is the operative instruction. Pull that chapter for claims processing guidance specific to digoxin therapeutic drug assay billing.
Not Covered Indications (No Specific Codes — Coverage Excluded by Clinical Scenario)
| Exclusion | Reason |
|---|---|
| Testing for patients on digitoxin | Different drug; digoxin assay not applicable |
| Testing for patients treated with digoxin FAB antibody | Assay is unreliable post-FAB; explicitly excluded by NCD 103 |
Key ICD-10-CM Diagnosis Codes
NCD 103 does not list specific ICD-10-CM codes in the policy document. Your MAC's LCD or the quarterly Covered Code List will specify which diagnosis codes support medical necessity for each covered indication. Common diagnoses that align with the covered indications — heart failure due to systolic dysfunction, atrial fibrillation, atrial flutter, digoxin toxicity, renal impairment — should map to the appropriate ICD-10-CM codes in your charge capture. Confirm the specific code list with your MAC before billing.
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