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M35.81 ICD-10-CM Code: Multisystem inflammatory syndrome

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

Coding at a Glance

Tabular directives
10 inclusion terms · 2 Excludes1 · 4 use-additional codes · 1 code-first instruction · 10 code-also instructions
Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 2

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 v43, Appendix B.

  • MS-DRG 545 — CONNECTIVE TISSUE DISORDERS WITH MCC (MDC 08)
  • MS-DRG 546 — CONNECTIVE TISSUE DISORDERS WITH CC (MDC 08)
  • MS-DRG 547 — CONNECTIVE TISSUE DISORDERS WITHOUT CC/MCC (MDC 08)

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 2 — Septicemia, Sepsis, Systemic Inflammatory Response Syndrome/Shock

Other models: CMS-HCC V22 HCC 2

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

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for M35.81 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 M35.81 itself; “inherited from” names the category or block whose note applies here.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

  • autoimmune disease NOS
  • collagen (vascular) disease NOS
  • systemic autoimmune disease
  • systemic collagen (vascular) disease

Source: inherited from M30-M36

Inclusion Terms

Alternative terms the tabular list files under this code.

  • MIS-A
  • MIS-C
  • Multisystem inflammatory syndrome in adults
  • Multisystem inflammatory syndrome in children
  • Pediatric inflammatory multisystem syndrome
  • PIMS

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

  • reactive perforating collagenosis (L87.1) inherited from M35Compare M35.81 vs L87.1 →
  • autoimmune disease, single organ or single cell-type -code to relevant condition category inherited from M30-M36

Code First

Underlying conditions that must be sequenced before this code.

  • Code first, if applicable, COVID-19 (U07.1)

Code Also

Additional codes that may be required to fully describe the encounter.

  • any associated complications such as:
  • acute hepatic failure (K72.0-)
  • acute kidney failure (N17.-)
  • acute myocarditis (I40.-)
  • acute respiratory distress syndrome (J80)
  • cardiac arrhythmia (I47-I49.-)
  • pneumonia due to COVID-19 (J12.82)
  • severe sepsis (R65.2-)
  • viral cardiomyopathy (B33.24)
  • viral pericarditis (B33.23)

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use additional code, if applicable, for:
  • exposure to COVID-19 or SARS-CoV-2 infection (Z20.822)
  • personal history of COVID-19 (Z86.16)
  • post COVID-19 condition (U09.9)

Coder workflow for M35.81

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

Before you code M35.81

  1. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with M35.81. 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 documentation support a condition named in M35.81’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.

    ReviewL87.1

  2. Is the underlying (etiologic) condition the Code First note names documented?
    Yes → Sequence the underlying condition first, then M35.81.
    No → Continue; do not add an underlying condition the record does not document.

Consider M35.81. Then work the Use Additional Code note and review the Code Also note, and 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).
The underlying (etiologic) condition
Named in the Code First note; sequenced before this code when documented (Guidelines I.A.13).
The conditions the Use Additional Code note names
Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.

Official instructions as workflow

  • Excludes1 — check before selecting M35.81(2 notes)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with M35.81: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareL87.1

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

  • Code First — sequencing check(1 note)

    Coding workflow: Check whether the underlying or etiologic condition the note names is documented. When it is, sequence it before M35.81. Do not add an underlying condition the record does not document.

    See the official tabular notes · Guidelines I.A.13

  • Use Additional Code — after identifying M35.81(4 notes)

    Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with M35.81 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

    ReviewZ20.822, Z86.16

    See the official tabular notes · Guidelines I.A.13

  • Code Also — related condition(10 notes)

    Coding workflow: Review the related condition when both are documented and the instruction applies. A Code Also note does not fix sequencing; the order follows the circumstances of the encounter.

    ReviewK72.0, N17, I40, J80, J12.82, R65.2

    See the official tabular notes · Guidelines I.A.17

Coding decision scenarios

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

Documentation: Both the condition M35.81 describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewL87.1

Documentation: The underlying condition the Code First note names is documented alongside this condition.

Coding question: How are the two sequenced?

Path: Review the Code First note.

Reason: The underlying condition is sequenced first and the manifestation follows (Guidelines I.A.13).

Documentation: A condition the Use Additional Code note names is documented.

Coding question: Is a second code reported with M35.81?

Path: Review the Use Additional Code note and the code it names.

Reason: The additional code is reported when the record documents the condition; a conditional instruction applies only when its condition is met (Guidelines I.A.13).

ReviewZ20.822, Z86.16

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

Multisystem inflammatory syndrome is a billable ICD-10-CM diagnosis code (M35.81).

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 (7)

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.

Official Coding Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Verbatim excerpts from the ICD-10-CM Official Guidelines for Coding and Reporting (CMS/NCHS) that govern this code.

Chapter 1: Certain Infectious and Parasitic Diseases (A00-B99), U07.1, U09.9 a. Human Immunodeficiency Virus (HIV) Infections 1) Code only confirmed cases

(l) Multisystem Inflammatory Syndrome For individuals with multisystem inflammatory syndrome (MIS) and COVID-19, assign code U07.1, COVID-19, as the principal/first-listed diagnosis and assign code M35.81, Multisystem inflammatory syndrome, as an additional diagnosis.

Chapter 1: Certain Infectious and Parasitic Diseases (A00-B99), U07.1, U09.9 a. Human Immunodeficiency Virus (HIV) Infections 1) Code only confirmed cases

If an individual with a history of COVID-19 develops MIS, assign codes M35.81, Multisystem inflammatory syndrome, and U09.9, Post COVID-19 condition, unspecified.

Chapter 1: Certain Infectious and Parasitic Diseases (A00-B99), U07.1, U09.9 a. Human Immunodeficiency Virus (HIV) Infections 1) Code only confirmed cases

If an individual with a known or suspected exposure to COVID- 19, and no current COVID-19 infection or history of COVID-19, develops MIS, assign codes M35.81, Multisystem inflammatory syndrome, and Z20.822, Contact with and (suspected) exposure to COVID-19.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

  1. Sequencing: 1 Code First instruction — the underlying condition is sequenced before this code when present. See the Code First notes
  2. 4 Use Additional Code instructions — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
  3. 10 Code Also notes — a second code may apply; the guidelines leave its sequencing to the circumstances of the encounter. See the Code Also notes
  4. 2 Excludes1 entries — codes named there are generally not reported together with this code (Guidelines I.A.12.a). See the Excludes1 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

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 M35.81 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: L94 — Other localized connective tissue disorders (via M35.-).

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

Referenced by 2 Excludes2 notes across 2 chapters: I77 — Other disorders of arteries and arterioles (via M35.-), J82 — Pulmonary eosinophilia, not elsewhere classified (via M35.-).

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

Referenced by 2 Code First instructions across 2 chapters: J84.170 — Interstitial lung disease with progressive fibrotic phenotype in diseases classified elsewhere (via M35.-), U09.9 — Post COVID-19 condition, unspecified.

Each of these codes carries a Code First note naming this condition — when that code is reported, THIS code is sequenced first, ahead of it.

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 2 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 3 MS-DRGs: DRG 545 (MDC 08), DRG 546 (MDC 08), DRG 547 (MDC 08).

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

Clinical classification (AHRQ CCSR):MUS024 — Systemic lupus erythematosus and connective tissue disorders (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.

M35.89 — Other specified systemic involvement of connective tissue

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Septicemia, Sepsis, Systemic Inflammatory Response Syndrome/Shock) for risk-adjusted payment.

A41.54 — Sepsis due to Acinetobacter baumannii, A41.59 — Other Gram-negative sepsis, A41.81 — Sepsis due to Enterococcus, A41.89 — Other specified sepsis, A41.9 — Sepsis, unspecified organism, A42.7 — Actinomycotic sepsis, A48.3 — Toxic shock syndrome, A54.86 — Gonococcal sepsis, B00.7 — Disseminated herpesviral disease, B37.7 — Candidal sepsis, P02.70 — Newborn affected by fetal inflammatory response syndrome, P36.0 — Sepsis of newborn due to streptococcus, group B, P36.10 — Sepsis of newborn due to unspecified streptococci, P36.19 — Sepsis of newborn due to other streptococci, P36.2 — Sepsis of newborn due to Staphylococcus aureus, P36.30 — Sepsis of newborn due to unspecified staphylococci, P36.39 — Sepsis of newborn due to other staphylococci, P36.4 — Sepsis of newborn due to Escherichia coli, P36.5 — Sepsis of newborn due to anaerobes, P36.8 — Other bacterial sepsis of newborn, +31 more

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Systemic lupus erythematosus and connective tissue disorders).

M35.05 — Sjögren syndrome with inflammatory arthritis, M35.06 — Sjögren syndrome with peripheral nervous system involvement, M35.07 — Sjögren syndrome with central nervous system involvement, M35.08 — Sjögren syndrome with gastrointestinal involvement, M35.09 — Sjögren syndrome with other organ involvement, M35.0A — Sjögren syndrome with glomerular disease, M35.0B — Sjögren syndrome with vasculitis, M35.0C — Sjögren syndrome with dental involvement, M35.1 — Other overlap syndromes, M35.2 — Behçet's disease, M35.3 — Polymyalgia rheumatica, M35.4 — Diffuse (eosinophilic) fasciitis, M35.5 — Multifocal fibrosclerosis, M35.6 — Relapsing panniculitis [Weber-Christian], M35.7 — Hypermobility syndrome, M35.8 — Other specified systemic involvement of connective tissue, M35.89 — Other specified systemic involvement of connective tissue, M35.9 — Systemic involvement of connective tissue, unspecified, M36.0 — Dermato(poly)myositis in neoplastic disease, M36.8 — Systemic disorders of connective tissue in other diseases classified elsewhere, +72 more

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.

Thyroid Stimulating Hormone (TSH)

Contextual Map

Every relationship of M35.81 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 M35.81 with these 15 related codes in Claim Check

Hierarchy

Use Additional Code

Code Also (11)

Referenced by Excludes1 notes

Referenced by Excludes2 notes

Referenced by Code First instructions

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 2 — Septicemia, Sepsis, Systemic Inflammatory Response Syndrome/Shock [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 08 — Diseases and Disorders of the Musculoskeletal System and Connective Tissue[MDC crossing]: “Diseases and Disorders of the Musculoskeletal System and Connective Tissue — 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. 18,508 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

  • MIS-A[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • MIS-C[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Multisystem inflammatory syndrome (in adult) (in children)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Pediatric inflammatory multisystem syndrome[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • PIMS[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Syndrome, multisystem inflammatory (in adults) (in children)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Syndrome, pediatric inflammatory multisystem[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (25)

Change history

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
Coding guidelines Official source data
ICD-10-CM Official Guidelines for Coding and Reporting (FY2026), quoted by section 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
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. "M35.81 — Multisystem inflammatory syndrome." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/m35.81-multisystem-inflammatory-syndrome

Change history

  • FY2022 — October 1, 2021
    Added to the code set
    Multisystem inflammatory syndrome
    FY2022 changes

Nearest Codes in This Family

Official ICD-10-CM classifications closest to M35.81 in its code family, with their registry titles.

View all codes in the M35 family