ICD-10 code S91.301A identifies an unspecified open wound of the right foot during the patient’s initial encounter for active treatment. It sits within Chapter 19 of the ICD-10-CM classification (Injury, Poisoning and Certain Other Consequences of External Causes) and is a fully billable, HIPAA-valid diagnosis code for fiscal year 2026 (effective October 1, 2025 through September 30, 2026). For coders and billers, this code surfaces regularly in emergency departments, urgent care settings, and outpatient wound care clinics — and its apparent simplicity masks several selection nuances that drive claim denials and audit flags when handled carelessly.
What Does ICD-10 Code S91.301A Mean?
S91.301A describes an open wound — meaning a break in the skin or underlying soft tissue — located on the right foot, where the wound type cannot be further specified as a laceration, puncture, bite, or incision at the time of the encounter. The 7th character “A” designates the initial encounter, indicating the patient is currently under active treatment for the injury.
Key attributes of this code at a glance:
- Billable/Specific: Yes — valid for claim submission
- Applicable setting: Emergency department, urgent care, outpatient wound care, office
- 7th character required: Yes — code S91.301 (without 7th character) is non-billable
- Laterality specified: Yes — right foot only; left foot uses S91.302A
- Unspecified type: Wound mechanism is not documented or determinable
- Valid fiscal year: FY 2026 (October 1, 2025–September 30, 2026)
What Conditions and Clinical Presentations Does S91.301A Cover?
S91.301A applies when a provider documents an open wound of the right foot but does not specify — or cannot specify — the exact wound morphology. In practice, this most often arises in two contexts: when a patient presents with a wound of unclear or mixed etiology, or when the provider’s documentation simply uses the term “open wound” without further characterization.
Clinical presentations appropriately captured under S91.301A include:
- Open wound of the right foot with no documented description of wound type
- Skin-break injuries to the dorsum (top) or plantar (sole) surface of the right foot where mechanism is ambiguous
- Wounds documented in triage or intake notes as “open wound” pending full provider assessment
- Injuries where the medical record lacks sufficient detail to support a more specific wound type code
What Does S91.301A Specifically Exclude?
The ICD-10-CM Excludes1 notes for the parent category S91 are mandatory and non-negotiable — the following conditions must not be coded with S91.301A:
- Open fracture of the right foot — use S92.- codes with 7th character “B” instead
- Traumatic amputation of the ankle and foot — use S98.- codes instead
- Any wound that can be clearly classified as a laceration, puncture, open bite, or foreign body wound (use the appropriate S91.3×1–S91.3×9 codes)
When Is S91.301A the Right Code to Use?
Selecting S91.301A requires more than confirming “right foot” and “open wound.” Coders must work through the following criteria before committing to this code:
- Confirm the wound is on the right foot — verify laterality in the provider’s examination notes, not just the chief complaint.
- Confirm the wound is genuinely open — a contusion, bruise, or closed injury does not qualify; the skin or mucosa must be broken.
- Confirm the wound type cannot be specified — if the note says “laceration,” use S91.311A (laceration without foreign body, right foot, initial encounter) instead.
- Confirm the appropriate 7th character — the patient must be under active treatment for this wound; “A” is correct even on a second or third visit if the wound is still being actively managed.
- Code also any associated wound infection — the official coding instruction at the S91 category level requires a secondary code for infection if present.
- Rule out excluded conditions — verify no open fracture or amputation is documented before finalizing.
How Does S91.301A Differ From S91.311A (Laceration Without Foreign Body, Right Foot)?
This is the most common code selection dilemma for this code family. The distinction rests entirely on documentation specificity.
| Feature | S91.301A | S91.311A |
|---|---|---|
| Code description | Unspecified open wound, right foot, initial encounter | Laceration without foreign body, right foot, initial encounter |
| When to use | Wound type not documented or determinable | Provider explicitly documents “laceration” |
| Documentation trigger | “Open wound,” no further detail | “Laceration,” “cut,” “incised wound” |
| Acceptable for unspecified wounds? | Yes | No — requires explicit laceration documentation |
| Audit risk | Low if truly unspecified; HIGH if laceration is documented | Low when documentation is clear |
| Foreign body version | S91.301A (no foreign body sub-codes at unspecified level) | S91.321A for laceration WITH foreign body |
In practice, coders frequently encounter provider notes that describe a wound type in one location (e.g., triage) but leave it as “open wound” in the final assessment. Always use the most specific code supported by the attending provider’s final documentation, not triage notes alone.
What Documentation Is Required to Support S91.301A?
Weak documentation is the root cause of the vast majority of claim denials and audits for open wound codes. Before assigning S91.301A, the supporting record must contain specific elements.
What Must the Provider Document in the Clinical Notes?
- Laterality confirmation — explicit reference to “right foot” in the examination or assessment
- Wound description — sufficient to establish an open wound exists (e.g., “skin disruption,” “open wound,” “break in skin integrity”)
- Absence of fracture — if imaging was performed, results should be noted; if no imaging was done, the clinical rationale should be clear
- Active treatment rendered — wound care, irrigation, dressing, suture, or referral must be documented to support the “initial encounter” designation
- Wound infection status — provider must state whether infection is present or absent; if present, a secondary code is required per coding instructions
- Mechanism of injury (preferred, not mandatory) — while S91.301A allows unspecified etiology, documenting mechanism (e.g., “stepped on debris”) strengthens medical necessity documentation and reduces audit exposure
Which Diagnostic or Lab Results Support This Code?
Unlike many ICD-10 codes, S91.301A does not require laboratory confirmation. However, the following findings commonly appear in the record and strengthen coding defensibility:
- Imaging results (X-ray or CT) ruling out underlying fracture
- Wound culture results (especially if infection is present, triggering an additional code)
- Wound measurement documentation (length × width × depth) — critical for CPT code pairing accuracy
- Tetanus immunization status documentation (standard of care in traumatic open wounds)
What Is the Documentation Standard for Inpatient vs. Outpatient Settings?
| Setting | Key Documentation Standard |
|---|---|
| Outpatient / ED | Principal or first-listed diagnosis; code the condition to the highest degree of certainty based on provider’s final assessment |
| Inpatient | Coded as principal diagnosis if the condition responsible for admission after study; uncertain diagnoses may be coded as confirmed per ICD-10-CM Official Coding Guidelines inpatient rules |
| Wound care clinic | First-listed diagnosis each visit; 7th character transitions to “D” (subsequent encounter) once active treatment is ongoing across multiple visits |
How Does S91.301A Affect Medical Billing and Claims?
S91.301A groups under MS-DRG 604 (Trauma to the Skin, Subcutaneous Tissue and Breast with MCC) or MS-DRG 605 (without MCC) for inpatient claims. For outpatient and ED encounters — far more common with this code — the following billing considerations apply:
- Medical necessity: Payers typically accept S91.301A as medically necessary for wound evaluation and treatment; the critical pairing is ensuring the procedure code (CPT) reflects the actual service rendered
- Unspecified codes: Per ICD-10-CM Official Coding Guidelines, unspecified codes like S91.301A are acceptable when clinical information is genuinely unknown — but payers may request documentation to confirm a more specific code was not available
- Decimal point in electronic filing: Do NOT include the decimal point when submitting electronically (submit as S91301A); some clearinghouses strip it, but omitting it proactively avoids rejections
- “Code also” instruction: The S91 category carries an official instruction to code also any associated wound infection — failing to report infection when documented is a compliance risk
What CPT or Procedure Codes Are Commonly Billed With S91.301A?
| CPT Code | Description | Typical Pairing Context |
|---|---|---|
| 99283 | ED E&M, moderate severity | Initial ED evaluation of open foot wound |
| 97597 | Debridement, open wound, first 20 sq cm | Active wound debridement during initial encounter |
| 12001 | Simple wound repair, 2.5 cm or less | Closure of superficial right foot wound |
| 12002 | Simple wound repair, 2.6–7.5 cm | Larger superficial closure at initial encounter |
| 97602 | Non-selective debridement, wet-to-dry | Conservative wound management |
| 28002 | Irrigation and drainage, foot | Deep wound requiring surgical irrigation |
| 99213/99214 | Office E&M | Outpatient follow-up still in active treatment (use “A”) |
Are There Any Prior Authorization or Coverage Restrictions?
- Medicare and most commercial payers do not require prior authorization for basic wound evaluation and simple repair; complex procedures (e.g., surgical debridement, CPT 97597+) may require prior auth under some plans
- Wound care clinic services should verify local coverage determinations (LCDs) — specifically L38294 (Wound Care) for Medicare — to ensure services are covered under the applicable diagnosis
- Workers’ compensation payers frequently require a detailed mechanism-of-injury narrative alongside the diagnosis code
What Coding Errors Should You Avoid With S91.301A?
Auditors reviewing S91.301A claims consistently identify a short list of errors that drive denials and compliance exposure:
- Using S91.301A when a more specific wound type is documented — if the note says “laceration,” the coder must use S91.311A or the appropriate laceration code, not the unspecified option
- Omitting the secondary infection code — when the provider documents cellulitis or wound infection, failing to add a code such as L03.115 (cellulitis of right foot) violates the “code also” instruction and may indicate undercoding
- Applying “A” (initial encounter) throughout the entire treatment course — “A” is correct only while the patient is under active treatment; once treatment is complete and the patient returns for follow-up of a healing wound, transition to “D” (subsequent encounter)
- Billing S91.301 (without 7th character) — this non-billable parent code will be rejected; all S91 codes require the 7th character
- Confusing right and left laterality — always confirm laterality in the provider’s physical exam section, not solely from the chief complaint or intake form
- Failing to code associated fracture separately — if an open fracture is also present, S91.301A is excluded; the fracture code from S92.- takes precedence with 7th character “B”
What Do Auditors Look for When Reviewing Claims With S91.301A?
- Provider documentation using specific wound-type language (e.g., “laceration”) that should have triggered a more specific code
- Absence of laterality confirmation in the examination body
- Missing “code also” infection code when clinical notes mention wound infection, erythema, or drainage
- Repeated use of “A” (initial encounter) across multiple visits spanning several weeks without documentation supporting ongoing active treatment
- Mismatch between wound size documented and CPT repair code selected
How Does S91.301A Relate to Other ICD-10 Codes?
Understanding where S91.301A sits within the broader S91 code family is essential for correct selection and sequencing.
| ICD-10 Code | Description | Relationship to S91.301A |
|---|---|---|
| S91.301D | Unspecified open wound, right foot, subsequent encounter | Same wound — use when active treatment is complete and patient returns for follow-up |
| S91.301S | Unspecified open wound, right foot, sequela | Late effect of the wound (e.g., scar, chronic pain resulting from original injury) |
| S91.302A | Unspecified open wound, left foot, initial encounter | Laterality distinction — opposite foot |
| S91.309A | Unspecified open wound, unspecified foot, initial encounter | Use only when laterality is truly undocumentable — not a substitute for failing to confirm laterality |
| S91.311A | Laceration without foreign body, right foot, initial encounter | More specific — use when laceration is documented |
| S91.321A | Laceration with foreign body, right foot, initial encounter | Use when laceration AND foreign body retention is documented |
| S91.331A | Puncture wound without foreign body, right foot, initial encounter | Use when a puncture is clearly documented |
| S92.311B | Displaced fracture of right foot (open) | Excludes1 — cannot be coded with S91.301A; replaces it when open fracture is present |
| L03.115 | Cellulitis of right foot | Secondary code — add alongside S91.301A when wound infection is documented |
What Is the Correct Code Sequencing When S91.301A Appears With Other Diagnoses?
- S91.301A as principal/first-listed — sequence first when the open wound is the reason for the encounter
- Secondary codes after S91.301A — add infection codes (e.g., L03.115) per the “code also” instruction
- External cause codes — per ICD-10-CM Official Coding Guidelines Chapter 20, an external cause code (e.g., W18.49XA — other slipping, tripping, or stumbling, initial encounter) is assigned secondarily to describe how the injury occurred; it is never sequenced as the principal diagnosis
- Comorbid chronic conditions — code chronic conditions like diabetes (E11.-) separately when they affect the clinical management of the wound
Real-World Coding Scenario — How S91.301A Is Applied in Practice
Patient encounter: A 42-year-old construction worker presents to the emergency department after cutting his right foot on a piece of scrap metal at a job site. The triage note reads “open wound, right foot.” The provider’s examination documents “approximately 3 cm break in skin integrity over the dorsum of the right foot with no apparent foreign body retained; X-ray negative for fracture; wound irrigated and closed with simple sutures.” No signs of infection are noted.
Correct Code Application
- S91.301A — Unspecified open wound, right foot, initial encounter (provider documented “break in skin integrity,” not explicitly “laceration”)
- 12002 — Simple repair, 2.6–7.5 cm (procedure code for the closure)
- W45.8XXA — Other foreign body or object entering through skin, initial encounter (external cause)
Why S91.301A and not S91.311A? The provider’s note says “break in skin integrity,” not “laceration.” In the absence of explicit wound-type language, the unspecified code is the correct, defensible choice. If the provider had written “laceration of right foot dorsum,” S91.311A would be required.
Common Mistake in This Scenario
- Incorrect code assigned: S91.311A (Laceration without foreign body, right foot, initial encounter)
- Why it fails: The provider never used the word “laceration” — this is coder interpretation, not provider documentation. Assigning a more specific code than the documentation supports is a diagnosis code specificity violation and can result in an audit finding of upcoding.
Frequently Asked Questions About ICD-10 Code S91.301A
Is ICD-10 Code S91.301A Valid for Use in 2026?
S91.301A is a valid, billable ICD-10-CM diagnosis code for fiscal year 2026, effective October 1, 2025 through September 30, 2026, with no changes to its description or validity status. Coders should verify annually against the ICD-10-CM Official Coding Guidelines published by CMS to confirm no structural updates have been made to the parent S91 category.
What Is the Difference Between S91.301A and S91.301D?
S91.301A is assigned when the patient is still under active treatment for the right foot open wound, regardless of how many visits have occurred. S91.301D (subsequent encounter) is used once the wound is in the healing phase and the patient returns for routine follow-up rather than active intervention — the 7th character reflects the phase of care, not the visit number.
Can S91.301A Be Used When a Laceration Is Documented?
No. If the provider explicitly documents a laceration of the right foot, the coder must use S91.311A (laceration without foreign body) or S91.321A (with foreign body). According to ICD-10-CM Official Coding Guidelines Section I.B, unspecified codes are acceptable only when clinical information is genuinely unknown or unavailable — not as a shortcut when more specific information exists in the record.
Does S91.301A Require a Secondary Code for Wound Infection?
S91.301A requires a “code also” secondary code for any associated wound infection present at the time of the encounter. If the provider documents cellulitis, purulent drainage, or other infection indicators alongside the open wound, omitting the secondary infection code (such as L03.115 for cellulitis of the right foot) constitutes incomplete coding and may constitute a compliance deficiency during coding audit preparation.
Is S91.301A Used for Diabetic Foot Wounds?
S91.301A is generally not appropriate for diabetic foot ulcers or chronic wounds attributable to diabetes. Diabetic foot wounds have their own combination codes in the E10–E11 range (e.g., E11.621 for Type 2 diabetes with foot ulcer). S91.301A is intended for traumatic open wounds — acute injuries — not chronic, disease-related ulcerations. Misapplying this code to a diabetic wound is a known audit target, particularly under revenue cycle compliance reviews.
Should the Decimal Point Be Included When Filing S91.301A Electronically?
Do not include the decimal point when submitting S91.301A on electronic claims. The correct electronic submission format is S91301A without the decimal. Including the decimal can cause HIPAA transaction set rejections; while some clearinghouses strip the decimal automatically, omitting it proactively eliminates that risk.
Key Takeaways
Correct application of ICD-10 code S91.301A depends on understanding both what it covers and its boundaries. Before finalizing this code on any claim, remember:
- S91.301A is billable for FY 2026 and requires the 7th character “A” — the parent code S91.301 alone is not billable
- “Initial encounter” means active treatment is ongoing, not that it’s the patient’s first visit — multiple active-treatment visits all use “A”
- The code is appropriate only when the wound type is genuinely unspecified — documented lacerations, punctures, or bites each have more specific codes
- Always “code also” any associated wound infection per the S91 category instruction
- Laterality must be confirmed in the provider’s examination notes — right foot (S91.301A) is not interchangeable with left foot (S91.302A) or unspecified foot (S91.309A)
- Exclude this code when an open fracture or traumatic amputation is present — those conditions have their own separate code families
- External cause codes from Chapter 20 should accompany S91.301A to document the mechanism of injury for complete ICD-10-CM Official Coding Guidelines compliance
For the most current coding guidance, always reference the CMS ICD-10-CM Tabular List and Official Guidelines and consult AHA Coding Clinic advisories for any condition-specific guidance updates.
