ICD code T23.732S – Third-degree corrosion of multiple left fingers, sequela

Key takeaways

T23.732S codes the sequela of a third-degree corrosion, or chemical burn, of two or more left fingers with the thumb not involved.

The fourth character 7 means corrosion of third degree, so a thermal third-degree burn of the same fingers takes T23.332S instead.

The residual condition, such as a scar or a contracture, is coded first, and T23.732S follows as its cause.

Corrosion codes carry a code-first note for T51–T65, which names the chemical and the intent behind the injury.

Side and thumb errors drive most denials. Right fingers take T23.731S, and an injury that includes the left thumb takes T23.742S.

ICD-10 code T23.732S: Definition and billable status

ICD-10 code T23.732S is the billable ICD-10-CM code for corrosion of third degree of multiple left fingers (nail), not including thumb, sequela. It applies once a full-thickness chemical injury to two or more left fingers has healed, and the patient is seen for what it left behind.

The code is valid in the current ICD-10-CM code set and is listed in the CDC/NCHS ICD-10-CM web tool. It needs no further characters. The left thumb sits outside its scope, and so does the right hand.

Four facts decide whether T23.732S fits a claim. The injury was chemical rather than thermal, and it reached full thickness. It involved at least two left fingers, with the thumb spared. It has now healed.

Code breakdown: What each character of T23.732S means

Every character in T23.732S carries one piece of the clinical picture. Change any one of them and the code describes a different injury.

Within subcategory T23.7-, the fifth character names the site of the corrosion:

• T23.71-: Thumb (nail)
• T23.72-: Single finger (nail) except thumb
• T23.73-: Multiple fingers (nail), not including thumb
• T23.74-: Multiple fingers (nail), including thumb
• T23.75-: Palm
• T23.76-: Back of hand
• T23.77-: Wrist
• T23.79-: Multiple sites of wrist and hand

Understanding the seventh character “S” for sequela encounters

The seventh character “S” marks a sequela, the late effect of an injury that has already healed. Under ICD-10-CM Official Guidelines Section I.B.10, the visit treats the residual condition, and the injury code explains its cause.

Three seventh-character options apply to T23.732. Each one tells a different clinical story:

Aftercare Z codes are not used with injury codes. While the wound heals, the “D” character covers routine follow-up. Once it has healed, “S” takes over.

Corrosion vs burn: Coding the correct category

ICD-10-CM separates burns from corrosions. A burn comes from heat, electricity or radiation, while a corrosion comes from a chemical. In category T23, the fourth character records both the mechanism and the depth.

The chart has to name the agent. A note reading “chemical burn from drain cleaner” supports T23.732S. A note reading “burn from a hot pan” sends the claim to T23.332S, even when the depth and fingers match.

Adjacent and commonly confused codes

One character separates T23.732S from a long list of neighbors. The table shows the codes that sit closest to it, each confirmed against the ICD-10-CM code set.

Side and thumb are the two details auditors check first. The right-hand equivalent is T23.731S, with a 1 in the sixth position. If the documented injury also reached the left thumb, T23.742S replaces T23.732S. The same healed corrosion on the left toes moves to category T25 as T25.732S.

Five checks against the note rule each neighbor in or out. Each failed check points to the code that fits instead.

What T23.732S covers and what it excludes

T23.732S supports any residual condition that is a direct late effect of a healed third-degree corrosion of two or more left fingers. The thumb must have been spared.

Residual conditions it can explain

• Hypertrophic or keloid scarring across the affected left fingers
• Scar contracture limiting flexion or extension of the left fingers
• Persistent pain or loss of sensation after the wound has healed
• Reduced grip or range of motion caused by scar tissue
• Nail deformity, pigment change or skin graft site problems after treatment

When to use a different code

• Active or unhealed corrosion: T23.732A for the initial encounter or T23.732D for a subsequent one
• Right fingers: T23.731S
• Left thumb involved as well: T23.742S, or T23.712S for the left thumb alone
• A single left finger: T23.722S
• Thermal rather than chemical injury: T23.332S for multiple left fingers, or T23.312S for the left thumb
• Partial-thickness injury: T23.632S for second degree or T23.532S for first degree

External cause and additional codes for T23.732S

Corrosion codes in category T23 carry a “code first” instruction for T51–T65. That code identifies the chemical and the intent. On a sequela claim it takes the seventh character “S” as well.

• T54.2X1S: Toxic effect of corrosive acids and acid-like substances, accidental (unintentional), sequela
• T54.3X1S: Toxic effect of corrosive alkalis and alkali-like substances, accidental (unintentional), sequela
• T54.1X1S: Toxic effect of other corrosive organic compounds, accidental (unintentional), sequela
• T54.91XS: Toxic effect of unspecified corrosive substance, accidental (unintentional), sequela. Use it only when the chart cannot name the agent.

Place of occurrence (Y92), activity (Y93) and external cause status (Y99) codes are reported only at the initial encounter. They do not return on a sequela claim.

Category T32 classifies corrosions by the body surface involved. The guidelines use it when the site is unspecified, or as an extra code when third-degree involvement reaches 20% or more of the body. A healed corrosion of several fingers rarely meets either test.

Coding T23.732S correctly: Sequencing and associated codes

Sequencing is where most T23.732S errors start. The residual condition is the first-listed diagnosis. T23.732S explains its cause and never leads the claim.

Correct sequencing example

• First-listed: The residual condition being treated, such as L90.5 (Scar conditions and fibrosis of skin), L91.0 (Hypertrophic scar) or M24.542 (Contracture, left hand)
• Next: The T51–T65 code for the chemical and intent, such as T54.2X1S for an accidental acid injury
• Then: T23.732S, the healed corrosion that caused the residual condition

The order on the claim has to match the reason for the visit in the clinical note. Submitting a clean claim for a corrosion sequela visit means the residual condition leads. Reversing that order is a common clearinghouse edit failure.

Pabau, the software we build for practice scheduling, notes and billing, submits electronic claims through the Claim.MD clearinghouse. Claim.MD runs its edit checks before the claim reaches the payer. A sequencing error then comes back to you, rather than to the payer as a denial.

Documentation requirements for T23.732S

Per ICD-10-CM Official Guidelines Section I.C.19, sequela coding needs two facts in the record. The original injury has healed, and a residual condition caused by it is being treated. T23.732S also needs the details that set it apart from its neighbors.

1. Healed status: The note states the corrosion has healed, with wording such as “healed chemical burn” or “mature scar tissue.”
2. Chemical agent and intent: The note names the substance and whether the exposure was accidental. That supports the T51–T65 code.
3. Side and digits: The note names the left hand and the fingers involved. It also confirms the thumb was not injured.
4. Depth of the original injury: The history records the corrosion as full thickness or third degree.
5. The residual condition: The note describes the scar, contracture or functional loss being treated today, so it can be coded first.

Practices that treat corrosion sequela in reconstructive or hand therapy settings benefit from building medical billing compliance requirements into the coding workflow. Missing details then surface before the claim goes out rather than after a denial.

Payer requirements and prior authorization for T23.732S

Payers expect more than correct code selection. Medicare, Medicaid and commercial plans each set documentation expectations for sequela visits, especially when surgery or wound care is billed with T23.732S.

• Proof of healing: A wound assessment confirming the third-degree corrosion of the left fingers has healed
• A link to the residual condition: The chart connects the scar, contracture or loss of function to the documented chemical injury
• Prior authorization for surgery: Scar revision, contracture release or skin grafting often needs approval from Medicare Advantage and commercial plans
• Support for wound care codes: Payers may want notes linking the treated site to the old injury when debridement or wound care is billed

Knowing the medical billing denial codes payers return on sequela claims helps you build a pre-submission checklist. The CMS ICD-10 codes guidance lists the annual code updates that affect Medicare claims.

Common claim denial reasons for T23.732S

Denials on T23.732S claims cluster around a short list of repeat errors. Checking for them before submission is the cheapest way to cut rework.

• Using “S” on an unhealed wound: An open or actively treated corrosion takes T23.732A or T23.732D, depending on the encounter.
• Listing T23.732S first: The residual condition must lead. A claim with T23.732S as the first-listed diagnosis fails sequencing edits.
• No residual condition code: T23.732S alone does not tell the payer what was treated. Pair it with a scar, contracture or similar code.
• Burn coded as corrosion, or the reverse: A thermal injury takes T23.332S. Check the agent in the note before you choose the category.
• Thumb or side mismatch: The note mentions the left thumb or the right hand, but the claim shows T23.732S. Use T23.742S or T23.731S instead.
• Missing chemical code: The code-first T51–T65 code is left off, or T54.91XS is used when the note names the substance.

Medical practice claims software with built-in edit checks catches side and sequencing errors before submission. The denial management workflows that work best pair those checks with a standard appeal template for disputed sequela claims.

How Pabau keeps T23.732S claims clean

In many practices, a scar revision visit is coded days later from a free-text note. The coder then has to work out the chemical, the side, the fingers and whether the thumb was involved. Each of those choices changes the code.

Pabau keeps the treatment note, the injury history and the insurance claim in one patient record. Its claims management tools build the claim from that record, so the coder works from the same note the clinician signed.

You spend less time chasing returned claims, and appeals start from a complete record rather than a rebuilt one.

Keep corrosion sequela claims tied to the note

Pabau keeps treatment notes and insurance claims in one patient record. The side, fingers and chemical your clinician documents are the details your claim is built on.

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Conclusion

T23.732S is narrow by design. Before you assign it, confirm four facts in the note. The agent was a chemical, and the injury was full thickness. Two or more left fingers were involved, with the thumb spared. The wound has healed.

If any of those is missing, query the clinician before the claim leaves. A one-line query costs far less than an appeal, and it protects the claim at audit as well as at payment.

Book a demo to see how Pabau keeps the clinical note and the corrosion sequela claim in step for your practice.

Continue your research

Need to understand how clearinghouse edits catch ICD-10 errors? Claim.MD clearinghouse overview explains how real-time edit checks intercept sequencing and character errors before payers see them.

Looking for a walkthrough of the ERA process after a sequela claim? Electronic remittance advice explained covers how to read ERA denial reason codes and action them efficiently.

Coding a corrosion sequela of the left foot? ICD-10 code T25.792S covers third-degree corrosion of multiple sites of the left ankle and foot, sequela.

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