2027 ICD-10-CM Diagnosis Code S27.301AUnspecified injury of lung, unilateral, initial encounter

ICD-10-CM Codes›S00–T88›S20-S29›S27

ICD-10-CM S27.301A
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

S27.301A is a billable ICD-10-CM diagnosis code for unspecified injury 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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 205 through 206, 963 through 965. 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 100 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Internal organ injury, initial encounter.

Code Identity

ICD-10-CM Code
S27.301A
Billable Status
Yes — Valid for Submission
Code Describes
Unspecified injury of lung, unilateral, initial encounter
Short Description
Unspecified injury of lung, unilateral, initial encounter
Same as the full description in the CMS dataset.
Parent Code
S27.301
Unspecified injury 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 CodeS27.301AUnspecified injury 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 2027, published by CMS and the National Center for Health Statistics.

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to S27.301A: its own notes plus those printed at S27, block S20-S29, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Block S20-S29 Injuries to the thorax applies to 1,602 codes
  • injuries of breast
  • injuries of chest (wall)
  • injuries of interscapular area

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From S27 Injury of other and unspecified intrathoracic organs applies to 162 codes
  • injury of cervical esophagus (S10-S19)
  • injury of trachea (cervical) (S10-S19)
From Block S20-S29 Injuries to the thorax applies to 1,602 codes
  • burns and corrosions (T20-T32)
  • effects of foreign body in bronchus (T17.5)
  • effects of foreign body in esophagus (T18.1)
  • effects of foreign body in lung (T17.8)
  • effects of foreign body in trachea (T17.4)
  • frostbite (T33-T34)
  • injuries of axilla
  • injuries of clavicle
  • injuries of scapular region
  • injuries of shoulder
  • insect bite or sting, venomous (T63.4)
From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • code to identify any retained foreign body, if applicable (Z18.-)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From S27 Injury of other and unspecified intrathoracic organs applies to 162 codes
  • any associated open wound of thorax (S21.-)

Notes

General instructions on how these codes are used.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
  • The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.

7th Character

Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.

From S27 Injury of other and unspecified intrathoracic organs applies to 162 codes
  • The appropriate 7th character is to be added to each code from category S27
Values for category S27 Encounter: Initial, Subsequent, Sequela
  • Ainitial encounter this code
  • Dsubsequent encounter
  • Ssequela

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name S27.301A, its category, or a range that includes it.

Code Also 3

These codes say S27.301A may also be needed to fully describe the condition. The note gives no sequencing direction.

  • S21 Open wound of thorax
    injury of intrathoracic organs (S27.-) names S27.-, which includes this code
  • S21 Open wound of thorax
    traumatic hemopneumothorax (S27.3) names S27.3, which includes this code
  • S22 Fracture of rib(s), sternum and thoracic spine
    injury of intrathoracic organ (S27.-) names S27.-, which includes this code

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 S27.301A 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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About S27.301AOverview

What is the ICD-10 code for unspecified injury of lung, unilateral, initial encounter?

The ICD-10-CM code for unspecified injury of lung, unilateral, initial encounter is S27.301A (sometimes written as S27301A). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is S27.301A (Unspecified injury of lung, unilateral) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report unspecified injury of lung, unilateral, initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What does the 7th character A in S27.301A mean?

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

What MS-DRG does S27.301A group to?

When unspecified injury of lung, unilateral, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 964, 965, 206, 205, 963, with relative weights from 0.9255 to 2.6361 depending on complications. Higher weights mean higher Medicare reimbursement.

Is S27.301A a CC or MCC?

CMS lists S27.301A as a CC (complication or comorbidity) for FY 2027. 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 100 closely related codes in its exclusion list.