I48.21 ICD-10-CM Code: Permanent atrial fibrillation
I48.21 maps to CMS-HCC V28 238 (RAF 0.299). Documentation must support MEAT. MEAT criteria · RAF calculator · free HCC coding tools
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FY 2026 Apr update / Diseases of the circulatory system (I00-I99) / Other forms of heart disease (I30-I5A)
I48.21
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidancePermanent atrial fibrillation
A permanent irregular heartbeat in the upper chambers of the heart that is accepted as the patient's baseline rhythm and will not be converted back to normal.
Buddy Insight
Permanent atrial fibrillation represents the final stage of atrial fibrillation progression where the decision has been made by the patient and provider to accept the arrhythmia as the baseline rhythm.
CMS-HCC V28
MappedHCC 238
RAF 0.299
CMS-HCC V24
MappedHCC 96
RAF 0.268
ACA/HHS
MappedHCC 142
Varies by metal level
ESRD/PACE
MappedHCC 96
RAF 0.049
RXHCC
MappedHCC 193
RAF 0.215
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for I48.21 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for I48.21 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for I48.21 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for I48.21 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for I48.21 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for I48.21 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for I48.21 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is I48.21 an HCC code?
Yes. I48.21 (Permanent atrial fibrillation) maps to Specified Heart Arrhythmias under the CMS-HCC V28 risk adjustment model (and Specified Heart Arrhythmias under V24), with a community non-dual aged RAF of 0.299. It is billable for payment year 2026.
Coder answer: I48.21 is billable and maps to V28 HCC 238, Specified Heart Arrhythmias. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- I48.21
- Description
- Permanent atrial fibrillation
- HCC (V28)
- HCC 238 — Specified Heart Arrhythmias
- RAF
- 0.299
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
Work I48.21 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for I48.21
For I48.21 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed I48.21 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
I48.21 is the ICD-10-CM diagnosis code for permanent atrial fibrillation. A permanent irregular heartbeat in the upper chambers of the heart that is accepted as the patient's baseline rhythm and will not be converted back to normal. I48.21 sits in the ICD-10-CM chapter for diseases of the circulatory system (i00-i99), within the section covering other forms of heart disease (i30-i5a).
Under the CMS-HCC V28 risk adjustment model, I48.21 maps to Specified Heart Arrhythmias (HCC 238) with a community, non-dual, aged base RAF weight of 0.299. Under the older V24 model, I48.21 mapped to the same category but with a base RAF weight of 0.268, V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Permanent AFib requires documentation that sinus rhythm is no longer a therapeutic goal, the provider accepts AFib as permanent and manages rate and anticoagulation only. A statement like 'permanent AFib, rate-controlled' supports the code. Because I48.21 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for I48.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Permanent AFib requires documentation that sinus rhythm is no longer a therapeutic goal, the provider accepts AFib as permanent and manages rate and anticoagulation only. A statement like 'permanent AFib, rate-controlled' supports the code.
- •Do not assign I48.21 when a cardioversion or antiarrhythmic strategy is still active in the chart, that supports I48.11 or I48.19 instead. Permanent means therapeutic surrender on rhythm control.
- •V28 HCC 238 at RAF 0.299. Permanent AFib is one of the most durable arrhythmia codes for year-over-year chart accuracy.
Clinical Significance
Permanent atrial fibrillation represents the final stage of atrial fibrillation progression where the decision has been made by the patient and provider to accept the arrhythmia as the baseline rhythm. Rhythm control is no longer pursued, and management focuses on rate control and anticoagulation. This classification has important treatment and prognostic implications.
Documentation Requirements
- ✓Provider documentation explicitly stating 'permanent' atrial fibrillation
- ✓Clinical decision documented that rhythm control will not be attempted
- ✓Electrocardiogram confirming atrial fibrillation
- ✓Rate control strategy and target heart rate documented
- ✓Anticoagulation regimen and stroke risk assessment
Commonly Confused Codes
- •I48.20: Chronic atrial fibrillation, unspecified; does not specify permanent acceptance
- •I48.11: Longstanding persistent atrial fibrillation; rhythm control may still be considered
- •I48.19: Other persistent atrial fibrillation; not yet classified as permanent
- •I48.0: Paroxysmal atrial fibrillation; intermittent, not permanent