ICD code T25.419S – Corrosion sequela of unspecified ankle

Key Takeaways

T25.419S is a billable ICD-10-CM code for a chemical burn sequela affecting an unspecified ankle site, distinct from thermal burn codes T25.0-T25.3

The seventh character S designates sequela, so the acute corrosion must be fully healed and a residual condition must drive the visit

More specific laterality codes (T25.411S for right, T25.412S for left) should replace T25.419S whenever the medical record documents the affected side

Pabau’s claims management software submits CMS-1500 claims electronically through Claim.MD and flags denied claims for rework

ICD-10 Code T25.419S: Quick Reference

ICD-10 Code T25.419S is valid for the current fiscal year under the ICD-10-CM system maintained by the CDC’s National Center for Health Statistics (NCHS). The table below summarizes the key attributes coders need before submitting a claim.

What T25.419S covers: Corrosion of unspecified degree of unspecified ankle, sequela

T25.419S covers a chemical or caustic injury to the ankle where neither the burn degree nor the affected side was documented. The patient now presents with residual effects rather than an active wound.

Each segment of the code descriptor carries a distinct coding implication. Misreading any one of them is enough to submit the wrong code:

• Corrosion: chemical or caustic agent (acid, alkali, industrial solvent). Not a flame, steam, or hot-surface injury.
• Unspecified degree: burn depth (first, second, third) was not documented. Use a degree-specific code whenever documentation supports it.
• Ankle: injury site within the T25 category, which covers the ankle and foot. This code covers the ankle, including the malleolar area. Foot and toe corrosions take their own codes (T25.42- and T25.43-).
• Unspecified site: laterality not documented. T25.411S (right ankle) or T25.412S (left ankle) is preferred when the record specifies.
• Sequela: encounter is for a residual condition after the acute injury has healed, not for the active wound itself.

Per the CMS ICD-10-CM Official Guidelines, coders must assign the highest level of specificity the documentation supports. Every “unspecified” axis in T25.419S represents an opportunity to query the provider if records include the missing detail.

Burn vs. corrosion in ICD-10-CM: Why two separate terms exist

ICD-10-CM separates thermal burns from corrosions because the causative agent determines both the treatment pathway and the external cause coding chain. Using a burn code (T25.0-T25.3) for a chemical injury, or vice versa, is a coding error that can trigger a medical necessity review.

When a patient’s chart mentions a chemical, acid, or caustic substance, always select a corrosion code (T25.4-T25.7). When the chart documents heat, fire, steam, or radiation, select the burn subblock (T25.0-T25.3). If the agent is unclear, query the provider before defaulting to unspecified.

Understanding the seventh character: T25.419A, T25.419D, and T25.419S differences

The seventh character in T25.419S encodes the encounter type and determines whether the visit covers the active injury, routine follow-up, or a residual condition. Applying the wrong character is a frequent source of denials on T25.4- sequela claims.

When to use T25.419S: sequela encounter guidelines for burn sequela ICD-10 coding

Use T25.419S only when the acute corrosion has completely healed and the current visit addresses a residual condition directly caused by that injury. Per ICD-10-CM Official Guidelines Sections I.B.10 and I.C.19.d, the sequela code is never used alone. The residual condition (for example, scar contracture, chronic pain, or functional impairment) is coded first, followed by T25.419S.

1. Confirm the acute injury is healed. If the wound is still open or actively being managed, use T25.419D instead.
2. Identify the residual condition. Code the late effect (e.g., scar contracture of the ankle) first, then sequence T25.419S as the cause.
3. Verify documentation supports sequela. The record must link the current residual condition to the prior chemical burn at the ankle.
4. Do not append another seventh character to the residual condition code. Only the injury code (T25.419S) carries the seventh character S.

Laterality and site specificity: More precise alternatives to ICD-10 Code T25.419S

T25.419S is the unspecified-laterality, unspecified-degree code. Most payers prefer the most specific code the documentation supports. Check the record for the affected side and burn degree before settling on T25.419S.

The laterality-specific codes (T25.411S and T25.412S) are the clinically preferred alternatives. Defaulting to T25.419S when the chart clearly states “right ankle chemical burn” is a specificity error that some payers flag on pre-payment review.

Coding T25.419S: Step-by-step documentation checklist

Complete documentation prevents denial before the claim is submitted. Submitting a clean claim for T25.419S requires the medical record to address each of the following points. Use this as a pre-submission checklist:

1. Confirm the causative agent is chemical. The record must identify an acid, alkali, or other caustic substance. Without this, the corrosion classification cannot be defended.
2. Verify the acute injury is fully healed. Progress notes or a prior encounter summary should document wound closure or healed status before applying the S seventh character.
3. Identify and code the residual condition first. Scar, contracture, chronic pain, functional limitation, or other sequela goes on line 1 of the claim. T25.419S sequences after it.
4. Confirm laterality. If the record specifies right or left, use T25.411S or T25.412S. Only use T25.419S when laterality is genuinely absent after querying the provider.
5. Assign the chemical and external cause codes. Code the chemical and intent from T51-T65, using the Table of Drugs and Chemicals. Add a Y92 place-of-occurrence code where applicable. These are reported alongside T25.419S, not in place of it.
6. Sequence correctly. Residual condition code first, then the T51-T65 chemical code, then T25.419S, then the Y92 place code.

External cause codes required with T25.419S

The Tabular List note at T25.4- tells coders to code first the T51-T65 code for the chemical and intent. It also asks for a Y92 code to identify the place of occurrence. Pabau integrates with the Claim.MD clearinghouse, so each claim is generated from the invoice and submitted electronically as a CMS-1500.

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Common claim denials and coding errors for T25.419S

Most denials on T25.419S trace back to four recurring errors. Understanding these patterns before submission is more effective than working them through denial management workflows after the fact.

Codes to use alongside T25.419S: Code-first and additional code rules

ICD-10-CM Tabular instructional notes govern how T25.419S interacts with other codes on the same claim. Sequela encounters follow different sequencing rules from initial or subsequent encounters. Misordering the codes is a common way to trigger a payer edit.

Code first (sequela sequencing): Per Official Guidelines I.B.10 and I.C.19.d, the residual condition is the principal diagnosis. Assign the code for the condition present, such as a scar contracture code from L90.x or a chronic pain code from G89.x. T25.419S follows as an additional code identifying the cause.

Use additional codes: External cause codes should accompany T25.419S where applicable, as described in the documentation checklist above. The WHO’s ICD-10 classification browser can support reference checks on the underlying injury taxonomy when complex multi-system corrosion cases require cross-referencing.

• Residual condition code (sequences first): scar contracture, chronic regional pain, limited range of motion, skin pigmentation change
• T51-T65 chemical code (sequences second): identifies the chemical and intent, with seventh character S
• T25.419S (sequences third): identifies the corrosion injury as the cause of the residual condition
• Y92 place code (supplementary): place of occurrence of the original injury

Payer-specific requirements and Medicare coverage notes for T25.419S

T25.419S has no national coverage determination (NCD) or local coverage determination (LCD) directly restricting its use as a diagnosis code. Payers evaluate medical necessity based on the principal residual condition code, not the sequela code itself. That said, several practical payer considerations apply:

• Medicare: CMS accepts T25.419S as a valid ICD-10-CM code. Medical necessity is reviewed against the residual condition code on line 1, not T25.419S alone. Claims pairing T25.419S with wound care CPT codes when the wound is described as healed can trigger a medical necessity audit.
• Commercial payers: Some plans require prior authorization for wound care services related to burn sequelae. Authorization is typically tied to the procedure code, but submitting T25.419S without a documented residual condition can delay approval.
• Specificity preferences: Many payers flag repeated use of unspecified codes (ending in 9) as a quality indicator. Consistent use of T25.419S when laterality is available in the chart can attract pre-payment review.

Practices using claims management software see every claim’s status in one dashboard. A denied T25.419S claim is flagged for rework as soon as the payer responds.

ICD-9-CM crosswalk for T25.419S

The ICD-9-CM equivalent for T25.419S maps approximately to subcategory 945 (burns of the lower limb) within the legacy 940-949 burn range. The General Equivalence Mappings (GEMs) crosswalk is approximate. ICD-9-CM had no seventh-character encounter system, so it needed a separate code to express sequela.

ICD-9-CM required a separate late-effect code (906.7 – late effect of burn of other extremities) to capture the sequela concept. ICD-10-CM embeds the encounter type in the seventh character instead. The structure is more compact, but coders must select the correct character at each encounter.

Conclusion

T25.419S is straightforward once the three unspecified axes are understood: degree, laterality, and encounter type. The most preventable error is applying the S seventh character while the wound is still active. Close behind are omitting the residual condition code that sequences first and defaulting to the unspecified code when the chart names the affected side.

Practices handling complex injury coding benefit from structured documentation workflows that connect clinical notes directly to claim submission. Pabau’s integrated claims management software submits CMS-1500 claims through Claim.MD and flags denied claims for rework. A rejected T25.419S claim is visible the day the payer returns it. To see how it works in a live practice environment, book a demo.

Continue your research

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