2026 ICD-10-CM Diagnosis Code M79.A21Nontraumatic compartment syndrome of right lower extremity

ICD-10-CM Codes›M00–M99›M70-M79›M79

ICD-10-CM M79.A21
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M79.A21 is a billable ICD-10-CM diagnosis code for nontraumatic compartment syndrome of right lower extremity. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 557 through 558. Coders also document this condition as bilateral nontraumatic compartment syndrome of lower limbs. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified connective tissue disease.

Code Identity

ICD-10-CM Code
M79.A21
Billable Status
Yes — Valid for Submission
Code Describes
Nontraumatic compartment syndrome of right lower extremity
Short Description
Nontraumatic compartment syndrome of right lower extremity
Same as the full description in the CMS dataset.
Parent Code
M79.A2
Nontraumatic compartment syndrome of lower extremity

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM70-M79Other soft tissue disorders
CategoryM79Other and unspecified soft tissue disorders, not elsewhere classified
This CodeM79.A21Nontraumatic compartment syndrome of right lower extremity

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral nontraumatic compartment syndrome of lower limbs
  • Nontraumatic compartment syndrome of left lower limb
  • Nontraumatic compartment syndrome of lower limb
  • Nontraumatic compartment syndrome of right lower limb

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MUS025
Other specified connective tissue disease
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

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Convert M79.A21 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
729.72 Nontraum comp syn-low ex
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M79.A21Overview

Is M79.A21 (Nontraumatic compartment syndrome of lower extremity) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report nontraumatic compartment syndrome of right lower extremity on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M79.A21 group to?

When nontraumatic compartment syndrome of right lower extremity is the principal diagnosis on an inpatient stay, it groups to MS-DRG 557, 558, with relative weights from 0.8932 to 1.4869 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M79.A21?

Under the General Equivalence Mappings, nontraumatic compartment syndrome of right lower extremity converts to ICD-9-CM 729.72 (nontraum comp syn-low ex). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.