2026 ICD-10-CM Diagnosis Code S27.309AUnspecified injury of lung, unspecified, initial encounter

ICD-10-CM Codes›S00–T88›S20-S29›S27

ICD-10-CM S27.309A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S27.309A is a billable ICD-10-CM diagnosis code for unspecified injury of lung, unspecified, 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. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Internal organ injury, initial encounter.

Code Identity

ICD-10-CM Code
S27.309A
Billable Status
Yes — Valid for Submission
Code Describes
Unspecified injury of lung, unspecified, initial encounter
Short Description
Unspecified injury of lung, unspecified, initial encounter
Same as the full description in the CMS dataset.
Parent Code
S27.309
Unspecified injury of lung, unspecified

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 CodeS27.309AUnspecified injury of lung, unspecified, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for S27.309A.

Unspecified codes
Unspecified codes exist in the ICD-10-CM classification for circumstances when documentation in the medical record does not provide the level of detail needed to support reporting a more specific code. However, in the inpatient setting, there should generally be very limited and rare circumstances for which the laterality (right, left, bilateral) of a condition is unable to be documented and reported. The following pages contain the list of unspecified ICD-10-CM diagnosis codes for which there is a more specific code to identify laterality (right, left, bilateral) within that code family.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acute lung injury
  • Chylothorax
  • Closed injury of lung
  • Direct acute lung injury
  • Indirect acute lung injury
  • Inhalation injury
  • Inhalation injury due to chemical
  • Injury due to chemical exposure
  • Injury of lung
  • Injury of lung with open wound into thorax
  • Injury of lung without open wound into thorax
  • Injury of pleura, lung or bronchus
  • Injury of thoracic cavity
  • Injury to heart and lung
  • Injury to lung during surgery
  • Injury to respiratory system due to inhalation of particulate matter
  • Lung injury with sepsis
  • Open injury of lung
  • Toxic inhalation injury
  • Traumatic chylothorax
  • Ventilator-associated lung injury

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

Clinical InformationClinical

  • Acute Lung Injury

    a condition of lung damage that is characterized by bilateral pulmonary infiltrates (pulmonary edema) rich in neutrophils, and in the absence of clinical heart failure. this can represent a spectrum of pulmonary lesions, endothelial and epithelial, due to numerous factors (physical, chemical, or biological).

  • Transfusion-Related Acute Lung Injury

    a rare but serious transfusion-related reaction in which fluid builds up in the lungs unrelated to excessively high infusion rate and/or volume (transfusion-associated circulatory overload). signs of transfusion-related acute lung injury include pulmonary secretions; hypotension; fever; dyspnea; tachypnea; tachycardia; and cyanosis.

  • Chylothorax

    the presence of chyle in the thoracic cavity. (dorland, 27th ed)

  • Traumatic Chylothorax

    accumulation of lymph fluid in the pleural cavity as a result of thoracic trauma.

  • Acquired Chylothorax

    chylothorax that results from malignancies (usually lymphoma), trauma to the thoracic duct, tuberculosis, or sarcoidosis.

  • Chylothorax

    an accumulation of chyle in the pleural cavity.

  • Chylothorax, CTCAE|Chylothorax|Chylothorax|Chylothorax

    a disorder characterized by milky pleural effusion (abnormal collection of fluid) resulting from accumulation of lymph fluid in the pleural cavity.

  • Chylothorax|Chylous Pleural Effusion

    a milky pleural effusion resulting from accumulation of lymph fluid in the pleural cavity. causes include malignancies (usually lymphoma), trauma to the thoracic duct, tuberculosis, sarcoidosis, and congenital causes.

  • Congenital Chylothorax

    chylothorax that is present at birth.

  • Grade 1 Chylothorax, CTCAE|Grade 1 Chylothorax|Grade 1 Chylothorax

    asymptomatic; clinical or diagnostic observations only; intervention not indicated

  • Grade 2 Chylothorax, CTCAE|Grade 2 Chylothorax|Grade 2 Chylothorax

    symptomatic; medical intervention indicated (e.g., fat-restricted diet); thoracentesis or tube drainage indicated

  • Grade 3 Chylothorax, CTCAE|Grade 3 Chylothorax|Grade 3 Chylothorax

    severe symptoms; elective operative intervention indicated

  • Grade 4 Chylothorax, CTCAE|Grade 4 Chylothorax|Grade 4 Chylothorax

    life-threatening respiratory or hemodynamic compromise; intubation or urgent intervention indicated

  • Grade 5 Chylothorax, CTCAE|Grade 5 Chylothorax|Grade 5 Chylothorax

    death

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 S27.309A 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 S27.309AOverview

Is S27.309A (Unspecified injury of lung, unspecified) a billable code?

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

What does the 7th character A in S27.309A mean?

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

What MS-DRG does S27.309A group to?

When unspecified injury of lung, unspecified, 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 S27.309A?

Under the General Equivalence Mappings, unspecified injury of lung, unspecified, 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.