2026 ICD-10-CM Diagnosis Code S27.391AOther injuries of lung, unilateral, initial encounter

ICD-10-CM Codes›S00–T88›S20-S29›S27

ICD-10-CM S27.391A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S27.391A is a billable ICD-10-CM diagnosis code for other injuries of lung, unilateral, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 205 through 206, 963 through 965. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Internal organ injury, initial encounter.

Code Identity

ICD-10-CM Code
S27.391A
Billable Status
Yes — Valid for Submission
Code Describes
Other injuries of lung, unilateral, initial encounter
Short Description
Other injuries of lung, unilateral, initial encounter
Same as the full description in the CMS dataset.
Parent Code
S27.391
Other injuries of lung, unilateral

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS20-S29Injuries to the thorax
CategoryS27Injury of other and unspecified intrathoracic organs
This CodeS27.391AOther injuries of lung, unilateral, initial encounter

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Injury of other and unspecified intrathoracic organs (S27). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

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

CCSR INJ010
Internal organ injury, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Chest Injuries and Disorders

The chest is the part of your body between your neck and your abdomen (belly). The medical term for your chest is thorax.

The full article covers:

  • What is the chest?
  • What are chest injuries and disorders?
  • How are chest injuries and disorders diagnosed?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert S27.391A to ICD-9-CMHistory

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

ICD-9-CM
861.20 Lung injury NOS-closed
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 S27.391AOverview

Is S27.391A (Other injuries of lung, unilateral) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other injuries of lung, unilateral, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in S27.391A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for other injuries of lung, unilateral, such as an emergency visit or first evaluation.

What MS-DRG does S27.391A group to?

When other injuries of lung, unilateral, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 205, 206, 963, 964, 965, with relative weights from 0.9405 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of S27.391A?

Under the General Equivalence Mappings, other injuries of lung, unilateral, initial encounter converts to ICD-9-CM 861.20 (lung injury NOS-closed). 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.