S21 vs S21.001A
S21 (Open wound of thorax) compared with S21.001A (Unspecified open wound of right breast, initial encounter), from the official CMS tabular data.
Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 20, 2026 · All releases and sources
Summary
These codes represent different levels of the same hierarchy: S21 is the non-billable header that contains S21.001A, so only S21.001A (or a sibling) is reported.
Registry fact- What is different?
The conditions named and billing status.S21 is “Open wound of thorax”; S21.001A is “Unspecified open wound of right breast, initial encounter”. S21 is a non-billable header; S21.001A is billable.
Registry fact
- Can these codes be reported together?
Not as a pair.S21 is the non-billable header that contains S21.001A. A header is not reported on a claim, so the choice is S21.001A or a sibling that matches the documentation.
Registry fact
- Is there an Excludes1 relationship?
None.Neither entry carries an Excludes1 note that names the other code. S21 carries 1 Excludes1 note and S21.001A carries 1 Excludes1 note covering other codes; the side-by-side table quotes them.
Official rule
- Is there an Excludes2 relationship?
None.Neither entry carries an Excludes2 note that names the other code. S21 carries 11 Excludes2 notes and S21.001A carries 11 Excludes2 notes covering other codes; the side-by-side table quotes them.
Official rule
- Is one more specific?
Yes.S21.001A is a subdivision of S21 in the tabular hierarchy, so it is the more specific of the two.
Registry fact
- Is one a parent or header code?
Yes.S21 is the non-billable header that contains S21.001A. A header stands for the whole family beneath it and is not reported on a claim.
Registry fact
- Are there sequencing instructions?
None.Neither entry carries a Code First or Use Additional Code note that names the other.
Official rule
- Are there other coding relationships?
None found.No laterality, encounter-phase, Table of Neoplasms, Table of Drugs and Chemicals, or history-versus-active-disease relationship links these codes.
MedCoder-derived
Official rule: a tabular instructional note or a section of the ICD-10-CM Official Guidelines, quoted as published. Registry fact: the codes’ own published attributes (titles, billable status, position in the hierarchy, code set). MedCoder-derived: a reading MedCoder computes from those facts; it is not itself a rule. How to read the labels
Can these codes be reported together?
Not as a pair — S21 is not reportable. S21 is the non-billable category that contains S21.001A.
A header stands for the whole family of codes beneath it and is not reported on a claim, so the choice is S21.001A or a sibling that matches the documentation. No Excludes1/Excludes2 relationship exists between these codes in the official tabular list.
Official guidance behind these answers
Section I.B.2 — Level of Detail in Coding · applies to: S21 and S21.001A
Diagnosis codes are to be used and reported at their highest number of characters available and to the highest level of specificity documented in the medical record. ICD-10-CM diagnosis codes are composed of codes with 3, 4, 5, 6 or 7 characters. Codes with three characters are included in ICD-10-CM as the heading of a category of codes that may be further subdivided by the use of fourth and/or fifth characters and/or sixth characters, which provide greater detail. A three-character code is to be used only if it is not further subdivided. A code is invalid if it has not been coded to the full number of characters required for that code, including the 7th character, if applicable.
ICD-10-CM Official Guidelines FY2027
Quoted from the ICD-10-CM Official Guidelines for Coding and Reporting in effect for the release shown. The tabular notes above are the code-level instruction; these sections are the convention that says how such a note is applied. Source document (CMS PDF) · Release and checksum
Side by side
| S21Open wound of thorax | S21.001AUnspecified open wound of right breast, initial encounter | |
|---|---|---|
| Billing status | Non-billable header Report instead: S21.001A, S21.001D, S21.001S, S21.002A, S21.002D | Billable |
| Classification | S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) | S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) |
| Definition | Open wound of thorax is a non-billable ICD-10-CM category code (S21). | Unspecified open wound of right breast, initial encounter is a billable ICD-10-CM diagnosis code (S21.001A). |
| 7th character | The appropriate 7th character is to be added to each code from category S21 | The appropriate 7th character is to be added to each code from category S21 |
| Includes | injuries of breast injuries of chest (wall) injuries of interscapular area | injuries of breast injuries of chest (wall) injuries of interscapular area |
| Excludes1 | traumatic amputation (partial) of thorax (S28.1) | traumatic amputation (partial) of thorax (S28.1) |
| Excludes2 | 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) | 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 | any associated injury, such as: injury of heart (S26.-) injury of intrathoracic organs (S27.-) rib fracture (S22.3-, S22.4-) spinal cord injury (S24.0-, S24.1-) traumatic hemopneumothorax (S27.3) traumatic hemothorax (S27.1) traumatic pneumothorax (S27.0) wound infection | any associated injury, such as: injury of heart (S26.-) injury of intrathoracic organs (S27.-) rib fracture (S22.3-, S22.4-) spinal cord injury (S24.0-, S24.1-) traumatic hemopneumothorax (S27.3) traumatic hemothorax (S27.1) traumatic pneumothorax (S27.0) wound infection |
Notes are the code’s own tabular entry, quoted as published. A note that names the other code is the one the verdict above rests on.
Derived from the official CMS ICD-10-CM tabular data (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources