2026 ICD-10-CM Diagnosis Code S21.421SLaceration with foreign body of right back wall of thorax with penetration into thoracic cavity, sequela
S21.421S is a billable ICD-10-CM diagnosis code for laceration with foreign body of right back wall of thorax with penetration into thoracic cavity, sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. 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. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury, sequela.
Code Identity
Code Classification
Present on Admission (POA)Billing
S21.421S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.
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 2026, published by CMS and the National Center for Health Statistics.
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 S21.421S to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S21.421SOverview
Is S21.421S a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report laceration with foreign body of right back wall of thorax with penetration into thoracic cavity, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character S in S21.421S mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the laceration with foreign body of right back wall of thorax with penetration into thoracic cavity itself has resolved, not the original event.
What MS-DRG does S21.421S group to?
When laceration with foreign body of right back wall of thorax with penetration into thoracic cavity, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 604, 605, with relative weights from 0.9160 to 1.4721 depending on complications. Higher weights mean higher Medicare reimbursement.
Is S21.421S exempt from POA reporting?
Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for laceration with foreign body of right back wall of thorax with penetration into thoracic cavity, sequela on inpatient claims.
What is the ICD-9 equivalent of S21.421S?
Under the General Equivalence Mappings, laceration with foreign body of right back wall of thorax with penetration into thoracic cavity, sequela converts to ICD-9-CM 906.0 (lt eff opn wnd head/trnk). 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.
