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I48.91 ICD-10-CM Code: Unspecified atrial fibrillation

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 96 · RxHCC V08 category 193

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v44, Appendix B.

  • MS-DRG 308 — CARDIAC ARRHYTHMIA AND CONDUCTION DISORDERS WITH MCC (MDC 05)
  • MS-DRG 309 — CARDIAC ARRHYTHMIA AND CONDUCTION DISORDERS WITH CC (MDC 05)
  • MS-DRG 310 — CARDIAC ARRHYTHMIA AND CONDUCTION DISORDERS WITHOUT CC/MCC (MDC 05)
  • MS-DRG 791 — PREMATURITY WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Risk Adjustment (CMS-HCC)

Payment categories this diagnosis maps to under CMS-HCC V28, payment year 2026.

  • HCC 238 — Specified Heart Arrhythmias

Other models: CMS-HCC V22 HCC 96 · RxHCC V08 HCC 193

Risk scores depend on the enrollee's full accepted diagnosis set and segment; a category mapping alone does not determine payment.

Coder workflow for I48.91

MedCoder structured workflow — derived from this code’s own official record

Before you code I48.91

  1. Unspecified does not mean incorrect. When the record gives no greater specificity, I48.91 may be the appropriate code. Check the record for detail that supports a more specific sibling. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

    See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

Choose the right path

  1. Does the record document the detail a more specific sibling code needs?
    Yes → Review the specific siblings in this subcategory.
    No → Continue — I48.91 is appropriate when the documentation goes no further.

Consider I48.91. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
Any detail beyond this code’s title
What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: The provider documents the condition in the terms of this code’s title and records no further detail.

Coding question: Is a more specific sibling code supportable?

Path: Review the subcategory for a sibling that names the missing detail.

Reason: A more specific code needs documentation of the distinguishing element; without it the unspecified code is appropriate, and a provider query is the route to specificity (Guidelines I.A.9.b, I.B.18).

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Unspecified atrial fibrillation is a billable ICD-10-CM diagnosis code (I48.91).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (1)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Verify Before Coding

  • No Medicare Code Editor or MS-DRG Definitions Manual restrictions apply to this code.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name I48.91 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Excludes2 note: R00 — Abnormalities of heart beat (via I48.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Referenced by 1 Code Also instruction: M35.81 — Multisystem inflammatory syndrome (via I48.-).

These codes suggest coding this condition alongside when both are present.

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 5 MS-DRGs: DRG 308 (MDC 05), DRG 309 (MDC 05), DRG 310 (MDC 05), DRG 791 (MDC 15), DRG 793 (MDC 15).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):CIR017 — Cardiac dysrhythmias (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Specified Heart Arrhythmias) for risk-adjusted payment.

I44.2 — Atrioventricular block, complete, I47.0 — Re-entry ventricular arrhythmia, I47.20 — Ventricular tachycardia, unspecified, I47.21 — Torsades de pointes, I47.29 — Other ventricular tachycardia, I47.9 — Paroxysmal tachycardia, unspecified, I48.0 — Paroxysmal atrial fibrillation, I48.11 — Longstanding persistent atrial fibrillation, I48.19 — Other persistent atrial fibrillation, I48.20 — Chronic atrial fibrillation, unspecified, I48.21 — Permanent atrial fibrillation, I48.3 — Typical atrial flutter, I48.4 — Atypical atrial flutter, I48.92 — Unspecified atrial flutter, I49.2 — Junctional premature depolarization, I49.5 — Sick sinus syndrome

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Cardiac dysrhythmias).

I47.29 — Other ventricular tachycardia, I47.9 — Paroxysmal tachycardia, unspecified, I48.0 — Paroxysmal atrial fibrillation, I48.1 — Persistent atrial fibrillation, I48.11 — Longstanding persistent atrial fibrillation, I48.19 — Other persistent atrial fibrillation, I48.2 — Chronic atrial fibrillation, I48.20 — Chronic atrial fibrillation, unspecified, I48.21 — Permanent atrial fibrillation, I48.3 — Typical atrial flutter, I48.4 — Atypical atrial flutter, I48.92 — Unspecified atrial flutter, I49.1 — Atrial premature depolarization, I49.2 — Junctional premature depolarization, I49.3 — Ventricular premature depolarization, I49.40 — Unspecified premature depolarization, I49.49 — Other premature depolarization, I49.5 — Sick sinus syndrome, I49.8 — Other specified cardiac arrhythmias, I49.9 — Cardiac arrhythmia, unspecified, +8 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Fibrillation”; these codes share that main term but sit in a different category of the Tabular List.

I49.01 — Ventricular fibrillation (ventricular), I49.89 — Other specified cardiac arrhythmias not elsewhere classified (heart), M62.89 — Other specified disorders of muscle (muscular)

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Iron Panel, Partial Thromboplastin Time (PTT) Test, Prothrombin Time Test and INR (PT/INR), Thyroid Stimulating Hormone (TSH)

Contextual Map

Every relationship of I48.91 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run I48.91 with these 2 related codes in Claim Check

Hierarchy

Referenced by Excludes2 notes

Referenced by Code Also instructions

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 238 — Specified Heart Arrhythmias [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 05 — Diseases and Disorders of the Circulatory System[MDC crossing]: “Diseases and Disorders of the Circulatory System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 15,708 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027
  • MDC 15 — Newborns and Other Neonates with Conditions Originating in Perinatal Period[MDC crossing]: “Newborns and Other Neonates with Conditions Originating in Perinatal Period — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs.”— CMS MS-DRG Definitions Manual · FY2027

Index entries

  • Fibrillation, atrial or auricular (established)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2027

Nearest codes (12)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v44 Release, file and checksum · Publisher’s page
Risk adjustment Official source data
2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "I48.91 — Unspecified atrial fibrillation." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/i48.91-unspecified-atrial-fibrillation

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Unspecified atrial fibrillation

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027, and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to I48.91 in its code family, with their registry titles.

View all codes in the I48 family