2026 ICD-10-CM Diagnosis Code S20.343AExternal constriction of bilateral front wall of thorax, initial encounter

ICD-10-CM Codes›S00–T88›S20-S29›S20

ICD-10-CM S20.343A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S20.343A is a billable ICD-10-CM diagnosis code for external constriction of bilateral front wall of thorax, 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 604 through 605, 963 through 965. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Superficial injury; contusion, initial encounter.

Code Identity

ICD-10-CM Code
S20.343A
Billable Status
Yes — Valid for Submission
Code Describes
External constriction of bilateral front wall of thorax, initial encounter
Short Description
External constrict of bilateral front wall of thorax, init
Parent Code
S20.343
External constriction of bilateral front wall of thorax

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS20-S29Injuries to the thorax
CategoryS20Superficial injury of thorax
This CodeS20.343AExternal constriction of bilateral front wall of thorax, initial encounter

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Superficial injury of thorax (S20). 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 INJ017
Superficial injury; contusion, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Code History & ChangesHistory

Replacement S20.343A replaces the following previously assigned code(s):

  • S20.341A - External constriction of right front wall of thorax, init
  • S20.342A - External constriction of left front wall of thorax, init
FY 2021AddedAdded to the ICD-10-CM code setEffective October 1, 2020.
FY 2022–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About S20.343AOverview

Is S20.343A (External constriction of bilateral front wall of thorax) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report external constriction of bilateral front wall of thorax, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in S20.343A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for external constriction of bilateral front wall of thorax, such as an emergency visit or first evaluation.

What MS-DRG does S20.343A group to?

When external constriction of bilateral front wall of thorax, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 604, 605, 963, 964, 965, with relative weights from 0.9160 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.

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.