ICD-10 Code T32.43: Corrosions involving 40-49% of body surface with 30-39% third degree corrosion

Key takeaways

ICD-10 Code T32.43 is a billable diagnosis code for corrosions involving 40-49% of body surface with 30-39% third degree corrosion.

The fourth character records how much of the body the corrosion covers, and the fifth records how much of the body is third degree.

The fifth character can never exceed the fourth, which is why the T32.4x family stops at T32.44.

Payers expect the causative chemical, a numeric TBSA figure, the third degree percentage, an assessment date, and a named clinician.

Digital intake forms and treatment notes in practice management software like Pabau capture both percentages at the point of care.

ICD-10 Code T32.43 is a billable diagnosis code for corrosions involving 40-49% of body surface with 30-39% third degree corrosion. It is valid for the 2026 edition, effective October 1, 2025.

Two documented percentages decide the code. The first is how much of the body the corrosive agent reached. The second is how much of the body is full thickness. This reference covers the classification logic, the documentation payers ask for, and where the code belongs on a claim.

ICD-10 Code T32.43: definition and billable status

T32.43 is a valid, billable ICD-10-CM diagnosis code. ICD-10-CM stands for International Classification of Diseases, 10th Revision, Clinical Modification. Assign the code when a corrosive agent has affected 40-49% of total body surface area, or TBSA. Of that whole-body total, 30-39% must be third degree.

The code sits in the T32 category, “Corrosions classified according to extent of body surface involved”. The Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics maintain it. You can confirm the current edition in the CDC/NCHS ICD-10-CM web tool.

T32.43 code description: the two percentages behind the code

Every T32 code carries two percentages, and both are measured against the whole body. The fourth character gives the total body surface area the corrosion covers. The fifth gives how much of that same total is third degree. Both figures have to be documented for the code to hold up on a claim.

Corrosions and thermal burns run through the same code ranges, so read each descriptor closely. Site-specific injuries use T20-T25, where the descriptor itself names the cause as thermal or chemical. The T30-T32 block then holds the extent codes: T31 for burns, such as T31.54, and T32 for corrosions. When a caustic chemical caused the injury, the corrosion code is the correct pick.

Practices that see chemical exposure cases should settle this question at the point of documentation. Digital intake forms that prompt for agent type, thermal or chemical, cut the number of coding corrections later. That prompt earns its place in dermatology EMR software too, since acid peel injuries turn up in an outpatient chart.

T32.43 in the ICD-10-CM code hierarchy

Knowing where the code sits helps you move between neighbors and avoid picking a header code by mistake.

• Chapter block: S00-T88 (Injury, poisoning and certain other consequences of external causes)
• Code block: T30-T32 (Burns and corrosions of multiple and unspecified body regions)
• Category: T32 (Corrosions classified according to extent of body surface involved)
• Subcategory: T32.4 (Corrosions involving 40-49% of body surface), a non-billable header
• Code: T32.43 (Corrosions involving 40-49% of body surface with 30-39% third degree corrosion), billable

Sibling codes under T32.4

Every T32.4x code shares the same fourth character, so all of them describe 40-49% TBSA. The fifth character sets the third degree percentage. Because that percentage is part of the same whole-body total, it can never exceed the band above it. That is why the family stops at T32.44.

The AAPC code lookup and the icd10data code page both carry the full sibling list for cross-reference. The next band up is T32.53, and teams reviewing extensive corrosion claims meet these codes together.

Understanding body surface area (TBSA) in T32.43 coding

The 40-49% band covers roughly half the body. Clinicians use two validated methods to estimate TBSA, and the note has to say which one produced the figure.

• Rule of Nines (adults): divides the body into segments of roughly 9% each. The head is 9%, each arm 9%, the front torso 18%, the back 18%, each leg 18%, and the perineum 1%. Both arms and both legs together reach 54%, above the T32.43 band.
• Lund-Browder chart (children and complex cases): adjusts each segment for age. It gives a more accurate figure in pediatric patients, where the Rule of Nines underestimates head proportion.

For coding, the note has to put the figure inside the 40-49% range. A record saying “approximately half the body”, with no number, will not support T32.43 and invites a payer audit. Structured note templates remove most of that ambiguity before it reaches a coder.

Third-degree corrosion: clinical and coding significance

Third-degree corrosion, also called full-thickness injury, destroys the epidermis and dermis and can reach subcutaneous tissue. The skin looks waxy, leathery, or charred, and it is usually insensate because the nerve endings are gone.

The fifth character measures full-thickness injury against the whole body, not against the corroded area alone. A patient with 45% TBSA corroded, of which 35% of the body is full thickness, codes to T32.43. If only 15% of the body is full thickness, the code is T32.41.

• First-degree corrosion: affects the epidermis only, with erythema and no blistering. It does not count toward the third degree figure.
• Second-degree corrosion: partial thickness, reaching the epidermis and part of the dermis. Blistering is present, and it does not count either.
• Third-degree corrosion: full-thickness destruction. This is what the 30-39% in T32.43 refers to.

Practices handling burn aftercare or wound management should record depth at every visit in their client record management system. The same detail feeds the procedure side, since plastic surgery EMR workflows draw on it when grafting is planned.

ICD-10-CM coding guidelines for T32.43

The ICD-10-CM Official Guidelines for Coding and Reporting govern T32 use. CMS and the National Center for Health Statistics publish them jointly. Three rules matter most for T32.43.

• Use T32 for unspecified or multiple sites: the extent categories apply when the corrosion covers several body regions. They also apply when the record does not name a site.
• Code the agent separately: add a code from category T54 to identify the corrosive substance.
• Sequencing: T32.43 leads the claim only when the site is unspecified. When the record names a site, the site-specific T20-T25 corrosion code is the principal diagnosis. T32.43 then follows as an additional code for extent.

Sequencing decides how much of the injury’s severity reaches the claim, and it feeds DRG assignment on an inpatient stay. Getting it wrong is a common source of rework, which is why medical billing compliance reviews look closely at burn and corrosion pairs.

Documentation requirements for T32.43

Missing documentation is the main audit risk for T32.43. Payers expect each of the following in the record before the code is supported.

• Causative chemical agent: name the substance, such as sulfuric acid, sodium hydroxide, or hydrofluoric acid. “Chemical burn” on its own is not enough.
• TBSA calculation: a numeric estimate, such as “45% TBSA by Rule of Nines”. It has to sit inside the 40-49% band.
• Depth breakdown: an explicit statement that 30-39% of the body is full thickness. A coder cannot infer that from photographs or procedure notes.
• Assessment date: TBSA and depth estimates can change over the first 48 to 72 hours. Say which assessment the percentages come from.
• Clinician attestation: name the estimating clinician. A figure recorded by a nurse without physician co-signature may not satisfy the payer.

Structured medical forms that prompt for each element cut the number of queries between coders and clinicians. Good denial management starts here, because an incomplete burn record gets caught in the billing queue instead of after a rejection.

Wording that points to the T32.4x family

Clinical notes describe extensive chemical injury in several ways. When a note uses any of these phrases, confirm both percentages before you settle on a fifth character.

• Chemical burn, described by extent rather than site
• Chemical corrosion involving 40-49% TBSA
• Acid burn, extensive, with TBSA documented at 40-49%
• Alkali burn, extensive, with TBSA documented at 40-49%
• Caustic burn, full and partial thickness combined, with 30-39% of the body at third degree

None of these phrases assigns T32.43 on its own. Each one still needs both figures in the record. Coders often see “chemical burn, extensive” and reach for a T32 code without checking either percentage.

Dermatology and med spa teams treating chemical peel complications hit this most often. Medical spa compliance records are where that level of detail should already sit.

How to use T32.43 in medical billing and claims

T32.43 has a clear place on the claim, but whether it leads or supports depends on the encounter.

Few code references say where T32.43 belongs in each of these scenarios. Keep the table above next to your scrubbing rules. Automated billing workflows can hold a rule that stops any T32.43 claim missing its T54 agent code. That is the cheapest place to protect a clean claim rate.

T32.43 does not carry a fee of its own. On an inpatient claim it feeds DRG assignment and severity weighting, so the extent figures affect payment indirectly. A grafting encounter pairs it with a procedure code such as 15150, and that code does carry a rate.

Related and adjacent ICD-10 codes

Coders working with T32.43 usually need a companion code, or need to confirm they picked the extent code rather than a site-specific one. The table below covers the closest neighbors.

Extent classification behaves the same way on the burn side of the block, so a coder who knows one family can read the other. Check the fourth character first, then the fifth, and the pair will hold up under review.

How Pabau keeps corrosion documentation and claims in step

Most practices split this work across tools. The TBSA estimate lands in one place, the consent and intake paperwork in another, and the claim is rebuilt from whatever the coder can find.

Practice management software like Pabau holds them together. Digital forms collect the agent, the TBSA figure, and the depth breakdown at the point of care. Every entry lands in the client record with a date and a named clinician.

Claims management software then builds the claim from that same record, so nobody retypes a percentage. From there the Claim.MD integration submits it electronically and tracks its status.

That is the route a medical claims clearinghouse gives you to any payer. Pabau does not pick the diagnosis code for you. It carries forward what the clinician documented, which is exactly what a T32 claim needs to survive review.

Keep corrosion coding backed by the record

Pabau’s digital forms and treatment notes capture the TBSA figure, the depth breakdown, and the clinician who signed off. Claims are then built from that record and submitted through Claim.MD, so extensive corrosion cases clear review the first time.

Book a demo

Conclusion

The code itself is straightforward. The difficulty sits upstream, in two numbers only the treating clinician can produce. Both need to reach the record while the patient is still being assessed.

Fix the note template and the coding follows. Leave it alone and every extensive corrosion case turns into an addendum request, a delay, and sometimes a denial you work twice.

One habit is worth keeping above all others: never let a qualitative TBSA description reach a T32 claim. Book a demo to see how Pabau captures those figures at the point of care and carries them onto the claim.

Continue your research

Need a structured approach to clinical documentation? Medical forms at your healthcare practice shows how standardized forms keep required fields from going missing.

Managing compliance records for chemical treatments? Medical spa compliance documentation sets out the recordkeeping and regulatory requirements for treatment providers.

Coding a lower extent band? T32.31 walks through the same two-character logic for corrosions covering 30-39% of body surface.

Waiting on payer approval before treatment? Prior authorization software explains how practices cut the wait between a request and a decision.

Frequently asked questions