J21.9 ICD-10-CM Code: Acute bronchiolitis, unspecified

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for J21.9 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on J21.9 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for J21.9

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

Before you code J21.9

1. Unspecified does not mean incorrect. When the record gives no greater specificity, J21.9 may be the appropriate code. Check the record for detail that supports a more specific sibling — in this subcategory the siblings differ by acute versus chronic. 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).

   ReviewJ21.0, J21.1, J21.8

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

2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with J21.9. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

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 — J21.9 is appropriate when the documentation goes no further.

   ReviewJ21.0, J21.1, J21.8

2. Does the documentation support a condition named in J21.9’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewJ44.89

Consider J21.9. 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).

Acuity

Acute or chronic as documented; when both are documented and separate codes exist, both are reported with the acute code first (Guidelines I.B.8).

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.

Official instructions as workflow

• Excludes1 — check before selecting J21.9(1 note)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with J21.9: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareJ44.89

  See the official tabular notes · Guidelines I.A.12.a

• Excludes2 — not part of J21.9(2 notes)

  Coding workflow: The conditions named in this note are not included in J21.9. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

  CompareJ84.115, J44.0

  See the official tabular notes · Guidelines I.A.12.b

Coding decision scenarios

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

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.

Indexed Clinical Terms (3)

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.

• Bronchiolitis (acute) (infective) (subacute)
• Bronchiolitis (acute) (infective) (subacute), with, bronchospasm or obstruction
• Bronchospasm (acute), with, bronchiolitis, acute

Don’t confuse J21.9 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of J21.9 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• J44.89— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of chronic bronchiolitis moves the case to J44.89; the two are not reported together unless documented as unrelated.

  Full comparison: J21.9 vs J44.89 →

• J84.115— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of respiratory bronchiolitis interstitial lung disease adds J84.115; it is not part of this code and both may be reported when both are documented.

  Full comparison: J21.9 vs J84.115 →

• J44.0— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of chronic obstructive pulmonary disease with acute lower respiratory infection adds J44.0; it is not part of this code and both may be reported when both are documented.

  Full comparison: J21.9 vs J44.0 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Verify Before Coding

• CC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

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 J21.9 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 Excludes1 note: J98.01 — Acute bronchospasm (via J21.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 1 Excludes2 note: J18.0 — Bronchopneumonia, unspecified organism (via J21.-).

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

Referenced by 1 Code Also instruction: D81.82 — Activated Phosphoinositide 3-kinase Delta Syndrome [APDS] (via J21.-).

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

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 14 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 2 MS-DRGs: DRG 202 (MDC 04), DRG 203 (MDC 04).

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

Clinical classification (AHRQ CCSR):RSP005 — Acute bronchitis (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 clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

J20.0 — Acute bronchitis due to Mycoplasma pneumoniae, J20.1 — Acute bronchitis due to Hemophilus influenzae, J20.2 — Acute bronchitis due to streptococcus, J20.3 — Acute bronchitis due to coxsackievirus, J20.4 — Acute bronchitis due to parainfluenza virus, J20.5 — Acute bronchitis due to respiratory syncytial virus, J20.6 — Acute bronchitis due to rhinovirus, J20.7 — Acute bronchitis due to echovirus, J20.8 — Acute bronchitis due to other specified organisms, J20.9 — Acute bronchitis, unspecified, J21.0 — Acute bronchiolitis due to respiratory syncytial virus, J21.1 — Acute bronchiolitis due to human metapneumovirus, J21.8 — Acute bronchiolitis due to other specified organisms

Same clinical category (CCSR)

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

J20.0 — Acute bronchitis due to Mycoplasma pneumoniae, J20.1 — Acute bronchitis due to Hemophilus influenzae, J20.2 — Acute bronchitis due to streptococcus, J20.3 — Acute bronchitis due to coxsackievirus, J20.4 — Acute bronchitis due to parainfluenza virus, J20.5 — Acute bronchitis due to respiratory syncytial virus, J20.6 — Acute bronchitis due to rhinovirus, J20.7 — Acute bronchitis due to echovirus, J20.8 — Acute bronchitis due to other specified organisms, J20.9 — Acute bronchitis, unspecified, J21.0 — Acute bronchiolitis due to respiratory syncytial virus, J21.1 — Acute bronchiolitis due to human metapneumovirus, J21.8 — Acute bronchiolitis due to other specified organisms, J40 — Bronchitis, not specified as acute or chronic

Same Index main term, other category

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

J44.81 — Bronchiolitis obliterans and bronchiolitis obliterans syndrome (obliterans), J44.89 — Other specified chronic obstructive pulmonary disease (chronic), J45.990 — Exercise induced bronchospasm (exercise induced), J68.0 — Bronchitis and pneumonitis due to chemicals, gases, fumes and vapors (chemical, acute), J68.4 — Chronic respiratory conditions due to chemicals, gases, fumes and vapors (chemical), J84.115 — Respiratory bronchiolitis interstitial lung disease (respiratory, interstitial lung disease), J84.89 — Other specified interstitial pulmonary diseases (obliterans, with organizing pneumonia), J98.01 — Acute bronchospasm

Contextual Map

Every relationship of J21.9 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 J21.9 with these 4 related codes in Claim Check

Hierarchy

• J00-J99 — Chapter 10: Diseases of the Respiratory System (J00-J99) (J00-J99)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• J20-J22 — Other acute lower respiratory infections[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Excludes1

• J44.89 — Other specified chronic obstructive pulmonary disease[Excludes1]: “chronic bronchiolitis (J44.89)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Excludes1 notes

• J98.01 — Acute bronchospasm[Excludes1](via J21.-): “acute bronchiolitis with bronchospasm (J21.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Excludes2 notes

• J18.0 — Bronchopneumonia, unspecified organism[Excludes2](via J21.-): “acute bronchiolitis (J21.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Code Also instructions

• D81.82 — Activated Phosphoinositide 3-kinase Delta Syndrome [APDS][Code Also](via J21.-): “other acute respiratory tract infections (J00-J06; J20-J22)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• RSP005 — Acute bronchitis[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

MS-DRG Grouper

• CC — Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (CC).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2026
• DRG 202 — BRONCHITIS AND ASTHMA WITH CC/MCC[MS-DRG]: “BRONCHITIS AND ASTHMA WITH CC/MCC (MDC 04)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 203 — BRONCHITIS AND ASTHMA WITHOUT CC/MCC[MS-DRG]: “BRONCHITIS AND ASTHMA WITHOUT CC/MCC (MDC 04)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 04 — Diseases and Disorders of the Respiratory System[MDC crossing]: “Diseases and Disorders of the Respiratory 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. 3,998 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

• Bronchiolitis (acute) (infective) (subacute)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Bronchiolitis (acute) (infective) (subacute), with, bronchospasm or obstruction[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Bronchospasm (acute), with, bronchiolitis, acute[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes

• J21 — Acute bronchiolitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• J21.0 — Acute bronchiolitis due to respiratory syncytial virus[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• J21.1 — Acute bronchiolitis due to human metapneumovirus[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• J21.8 — Acute bronchiolitis due to other specified organisms[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

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 FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 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 — v43 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

Nearest Codes in This Family

Official ICD-10-CM classifications closest to J21.9 in its code family, with their registry titles.

• J21 — Acute bronchiolitis
• J21.0 — Acute bronchiolitis due to respiratory syncytial virus
• J21.1 — Acute bronchiolitis due to human metapneumovirus
• J21.8 — Acute bronchiolitis due to other specified organisms

View all codes in the J21 family