S21.409A — Unspecified open wound of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter
Is S21.409A billable?
Yes, but S21.409A will trip a Medicare edit. S21.409A is a valid, billable ICD-10-CM code for encounters from October 1, 2026 through September 30, 2027. However, CMS lists S21.409A under Medicare Code Editor edit 20, “Unspecified code” — meaning a code specifying laterality (right, left or bilateral) exists in the same family. On an inpatient claim this triggers the edit, because CMS holds that there are very limited circumstances in which laterality cannot be documented.
More specific alternatives
- S21.411ALaceration without foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter
- S21.421ALaceration with foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter
- S21.431APuncture wound without foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter
- S21.441APuncture wound with foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter
- S21.451AOpen bite of right back wall of thorax with penetration into thoracic cavity, initial encounter
S21.409A at a glance
| Code | S21.409A |
|---|---|
| Description | Unspecified open wound of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
| 7th character "A" | initial encounter |
What does the 7th character "A" mean in S21.409A?
In S21.409A, the 7th character A means initial encounter. The 7th character is required for S21.409A to be a valid, complete code.
Same condition, different episode of care — switch the 7th character:
What Medicare edits apply to S21.409A?
The Medicare Code Editor screens inpatient claims before they are grouped. These edits name S21.409A directly.
A code specifying laterality (right, left or bilateral) exists in the same family. CMS holds that there are very limited circumstances in which laterality cannot be documented.
Which MS-DRGs does S21.409A group to?
S21.409A sits in MDC 21 and helps define the logic of 2 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 913Traumatic Injury with MCCmedical
- 914Traumatic Injury without MCCmedical
As a secondary diagnosis, S21.409A is a major complication or comorbidity (MCC), which can move a stay into a higher-paying DRG.
How is S21.409A listed in the Alphabetic Index?
The Alphabetic Index lists these routes under S21.40, the nearest indexed parent of S21.409A. Use them to find the family, then select the specific code.
- Wound, open › thorax, thoracic › back › with penetration
Excludes1 — never code together — inherited from S21
The conditions below can never be reported together with S21.409A on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
- traumatic amputation (partial) of thorax (S28.1)
Use additional code — inherited from Chapter 19
Report an additional code alongside S21.409A to fully describe the condition. S21.409A is sequenced first.
- code to identify any retained foreign body, if applicable (Z18.-)
Excludes2 — not included here — inherited from Chapter 19
The conditions below are not part of S21.409A, but a patient may have both at the same time. When documentation supports it, S21.409A and the excluded code may both be reported.
Excludes2 — not included here — inherited from S20-S29
The conditions below are not part of S21.409A, but a patient may have both at the same time. When documentation supports it, S21.409A and the excluded code may both 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)
Code also — inherited from S21
Two codes may be needed to describe the condition fully. Whether S21.409A is sequenced first depends on the reason for the encounter.
How long has S21.409A existed?
S21.409A has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.