2027 ICD-10-CM Diagnosis Code S21.431APuncture wound without foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter
ICD-10-CM Codes›S00–T88›S20-S29›S21
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- 7th Character A — Initial Encounter
- Not Chronic
S21.431A is a billable ICD-10-CM diagnosis code for puncture wound without foreign body of right back wall of thorax with penetration into thoracic cavity, 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 913 through 914, 963 through 965. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 93 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Open wounds of trunk, initial encounter.
Code Identity
Code Classification
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Open wound of thorax (S21). 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 S21.431A: its own notes plus those printed at S21, 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.
- injuries of breast
- injuries of chest (wall)
- injuries of interscapular area
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
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.
- 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)
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- 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.
Notes
General instructions on how these codes are used.
- 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.
- The appropriate 7th character is to be added to each code from category S21
- 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 S21.431A, its category, or a range that includes it.
Code Also 6
These codes say S21.431A may also be needed to fully describe the condition. The note gives no sequencing direction.
- S23.1 Subluxation and dislocation of thoracic vertebraopen wound of thorax (S21.-) names S21.-, which includes this code
- S24 Injury of nerves and spinal cord at thorax levelopen wound of thorax (S21.-) names S21.-, which includes this code
- S25 Injury of blood vessels of thoraxany associated open wound (S21.-) names S21.-, which includes this code
- S26 Injury of heartopen wound of thorax (S21.-) names S21.-, which includes this code
- S27 Injury of other and unspecified intrathoracic organsany associated open wound of thorax (S21.-) names S21.-, which includes this code
- S29 Other and unspecified injuries of thoraxany associated open wound (S21.-) names S21.-, which includes this code
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Back Injuries
Your back is made of bones, muscles, and other tissues extending from your neck to your pelvis. Back injuries can result from sports injuries, work around the house or in the garden, or a sudden jolt such as a car accident. The lower back is the most common site of back injuries and back pain. Common back injuries include :
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert S21.431A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S21.431AOverview
Is S21.431A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report puncture wound without foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character A in S21.431A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for puncture wound without foreign body of right back wall of thorax with penetration into thoracic cavity, such as an emergency visit or first evaluation.
What MS-DRG does S21.431A group to?
When puncture wound without foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 964, 965, 914, 913, 963, with relative weights from 0.9281 to 2.6361 depending on complications. Higher weights mean higher Medicare reimbursement.
Is S21.431A a CC or MCC?
CMS lists S21.431A as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 93 closely related codes in its exclusion list.
Can S21.431A be reported with S28.1?
Not as a rule. The Excludes1 note at S21, which applies to S21.431A, lists "traumatic amputation (partial) of thorax (S28.1)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
