2026 ICD-10-CM Diagnosis Code M35.81Multisystem inflammatory syndrome
ICD-10-CM Codes›M00–M99›M30-M36›M35
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 2
- Chronic Condition
M35.81 is a billable ICD-10-CM diagnosis code for multisystem inflammatory syndrome. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 545 through 547. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 2 closely related codes. Coders also document this condition as multisystem inflammatory syndrome in adults. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Systemic lupus erythematosus and connective tissue disorders.
For Medicare Advantage risk adjustment, M35.81 maps to CMS-HCC Category 2 (Septicemia, Sepsis, Systemic Inflammatory Response Syndrome/Shock) under the V28 model, adding a risk factor of about 0.500 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
M35.81 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Multisystem inflammatory syndrome in adults
- Multisystem inflammatory syndrome in children
- Systemic inflammatory response syndrome
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- MIS-A
- MIS-C
- Multisystem inflammatory syndrome in adults
- Multisystem inflammatory syndrome in children
- Pediatric inflammatory multisystem syndrome
- PIMS
Code First
- , if applicable, COVID-19 U07.1
Code Also
- 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
- 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
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions, the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation. Wherever such a combination exists, there is a "use additional code" note at the etiology code, and a "code first" note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.
A "code also" note instructs that two codes may be required to fully describe a condition, but this note does not provide sequencing direction.
The “use additional code” indicates that a secondary code could be used to further specify the patient’s condition. This note is not mandatory and is only used if enough information is available to assign an additional code.
Index to Diseases and InjuriesGuidance
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Systemic Inflammatory Response Syndrome
a systemic inflammatory response to a variety of clinical insults, characterized by two or more of the following conditions: (1) fever >38 degrees c or hypothermia <36 degrees c; (2) tachycardia >90 beat/minute; (3) tachypnea >24 breaths/minute; (4) leukocytosis >12,000 cells/cubic mm or 10% immature forms. while usually related to infection, sirs can also be associated with noninfectious insults such as trauma; burns; or pancreatitis. if infection is involved, a patient with sirs is said to have sepsis.
Patient EducationClinical
Connective Tissue Disorders
Your connective tissue supports many different parts of your body, such as your skin, eyes, and heart. It is like a "cellular glue" that gives your body parts their shape and helps keep them strong. It also helps some of your tissues do their work. It is made of many kinds of proteins. Cartilage and fat are types of connective tissue.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Code History & ChangesHistory
Replacement M35.81 replaces the following previously assigned code(s):
- M35.8 - Other specified systemic involvement of connective tissue
Questions About M35.81Overview
What is the ICD-10 code for multisystem inflammatory syndrome?
The ICD-10-CM code for multisystem inflammatory syndrome is M35.81 (sometimes written as M3581). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is M35.81 (Other specified systemic involvement of connective tissue) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report multisystem inflammatory syndrome on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does M35.81 group to?
When multisystem inflammatory syndrome is the principal diagnosis on an inpatient stay, it groups to MS-DRG 545, 546, 547, with relative weights from 0.8362 to 2.4817 depending on complications. Higher weights mean higher Medicare reimbursement.
Is M35.81 a CC or MCC?
CMS lists M35.81 as a CC (complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 2 closely related codes in its exclusion list.
What HCC is M35.81?
M35.81 (multisystem inflammatory syndrome) maps to CMS-HCC Category 2 (Septicemia, Sepsis, Systemic Inflammatory Response Syndrome/Shock), commonly written as HCC 2, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 2 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does M35.81 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, M35.81 adds a risk adjustment factor of about 0.500 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.447 to 0.780 depending on the payment segment). HCC 2 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 2 category page.
