ICD code T32.74 – Corrosions involving 70-79% body surface with 40-49% third degree

Key takeaways

T32.74 is billable under the 2026 ICD-10-CM edition, effective for dates of service from October 1, 2025.

The record has to carry two separate figures: total body surface of 70-79%, and third degree surface of 40-49%.

The fourth character reports total extent and the fifth character reports the third degree share.

Corrosions are chemical injuries, so a note describing flame or scald damage rules this code out.

Pabau pre-fills the claim from the encounter record and keeps an ICD-10 code library on the same screen.

ICD-10 code T32.74 is billable exactly as it stands

ICD-10 code T32.74 is the billable ICD-10-CM diagnosis code for corrosions involving 70-79% of body surface with 40-49% third degree corrosion. It took effect on October 1, 2025, under the 2026 edition of the CMS ICD-10-CM tabular list. Medicare, Medicaid and most commercial payers process it as submitted.

It also needs no seventh character. Plenty of T-chapter injury codes demand an encounter-stage qualifier of initial, subsequent or sequela, and a missing one sends the claim straight back. T32.74 is complete as written, which removes that failure point entirely.

A complete code line is not the same as a clean claim, though. T32.74 reports extent and nothing else, so a payer still expects an anatomic-site code and an external-cause code beside it. Submit the extent code alone and an edit fires before anyone reads the chart.

Neither T32 nor T32.7 belongs on a claim line

T32.74 sits three levels deep in the ICD-10-CM hierarchy, and only the deepest level is billable. Send a parent code instead of the full five characters and the claim returns as non-specific. That is a rework ticket rather than a denial you can appeal, so it costs a cycle either way.

The AAPC Codify ICD-10-CM lookup confirms T32.7 as a header only. Every billable code in the subcategory sits at the fifth-character level, running T32.70 through T32.77.

The two percentages in T32.74 measure different things

T32.74 asks for two measurements at once, and they are not interchangeable. The first is how much body surface the corrosion covers at any depth. The second is how much of that surface is full thickness.

Fourth character, the 7 in T32.7x: total corrosion coverage runs 70-79% of body surface, counting every depth together.

Fifth character, the 4 in T32.x4: of that total, 40-49% of body surface is third degree. Third-degree corrosion destroys every layer of skin and can reach subcutaneous tissue.

Both figures come from the rule of nines in adults. The head and neck take 9%, and so does each arm. Each leg and each trunk surface take 18%, and the perineum takes 1%. Pediatric patients get the Lund-Browder chart instead, since it adjusts for a proportionally larger head and shorter legs. According to the CDC/NCHS ICD-10-CM web tool, the note should record which method produced the figure, so an auditor can follow the arithmetic.

Laid side by side, the eight codes in the subcategory make the pattern plain.

Why the 40-49% band changes the code

The fifth character is what separates T32.74 from its neighbors, not the fourth. A patient with 75% of body surface involved but only 20% third degree codes to T32.72, even though the total is identical.

Confusing total surface with third-degree surface is the most frequent error in this subcategory. Both numbers therefore have to appear separately in the note before anyone assigns the fifth character.

Corrosion or burn? The documented cause decides

A corrosion is a chemical injury and a burn is a thermal one, and the cause in the record sorts them. The numeric ranges do not. Anatomic-site injuries run T20-T28 for both, with T29 covering multiple body regions.

The descriptors inside each category say whether the injury is a burn or a corrosion. Only the extent codes split by mechanism: T31 for burns, T32 for corrosions. Section I.C.19.d of the ICD-10-CM Official Guidelines, “Coding of Burns and Corrosions”, sets out the rules for both.

Picking T32.74 where the record describes a flame or a scald is a coding error, and it surfaces on audit rather than at submission. Corrosion coding only holds up when the chemical itself is named in the documentation.

Eight sibling codes, one character apart

The T32.7 subcategory holds eight billable codes. Each carries the same 70-79% total body surface and differs only in the fifth character, which reports the third degree share. Coders on major corrosion cases move between them as the depth assessment gets revised.

Severity reads as a straight ladder here, and T32.74 sits in the middle of it, with roughly half of the involved surface full thickness.

Our full ICD-10-CM code index carries the anatomic-site and external-cause codes that travel with it.

Chart phrasings that should resolve to this code

Clinicians rarely write the word “corrosion”. The phrasings below all describe what T32.74 covers, and each should land on it during code assignment. None of them is an alternate code.

• Corrosion of 70 to 79 percent of body surface with 40 to 49 percent third degree corrosion
• Chemical burn (corrosion) involving 70-79% TBSA, 40-49% full thickness
• Full-thickness chemical corrosion, 40-49% of body surface, total involvement 70-79%
• Corrosion 70-79% body surface, third-degree 40-49%
• Chemical corrosion with 40-49% deep (third degree) involvement out of 70-79% total TBSA

The WHO ICD-10 browser classifies corrosions in parallel with burns, across the same anatomic and severity axes. So a note reading “chemical burn” should be read as a corrosion, provided a chemical agent is named as the cause.

What section I.C.19.d asks of corrosion coding

Section I.C.19.d of the ICD-10-CM Official Guidelines for Coding and Reporting, “Coding of Burns and Corrosions”, governs the whole T32 category. Five points do most of the work on a T32.74 chart.

• Sequence by highest severity. Where several sites are corroded, the anatomic-site code for the deepest injury comes first. T32.74 reports extent, so it usually sits in a secondary position rather than leading the claim.
• Site codes and extent codes do different jobs. T20-T28 identifies where the corrosion is and how deep it goes. The T32 code reports overall extent. Guidance advises assigning it when the site is unspecified, or when the extent figure is needed for burn mortality data.
• Name the agent. A code identifying the chemical substance belongs alongside T32.74. Payer edit software increasingly rejects T32 codes that arrive without one.
• Separate codes per site and depth. Where sites differ in depth, each gets its own code. The T32 code still reports the overall picture.
• Non-healing corrosions stay acute. A corrosion that has not healed is coded as a current injury, not as a late effect.

What those five points add up to is simple enough. T32.74 is almost always part of a code cluster. Practices handling these cases should build a code-set template with the anatomic, extent and external-cause slots already in it.

Documentation that keeps the claim from bouncing

Five elements have to be in the chart before T32.74 is defensible. Payer audit teams request records on major corrosion cases as a matter of routine, and a missing element is a clawback waiting to happen.

• Total body surface involvement (70-79%): the note states the surface involved across all depths, backed by a rule-of-nines or Lund-Browder calculation.
• Third-degree sub-measurement (40-49%): a separate figure for the full-thickness component. A note recording only overall extent cannot support the fifth character.
• Chemical causative agent: the record names or describes the chemical, such as hydrochloric acid, sodium hydroxide or an industrial solvent. “Chemical exposure” on its own is not enough.
• Anatomic sites affected: T32.74 reports extent, not location. At least one site code from T20-T28 should accompany it to identify the region involved.
• External-cause code: a code from the relevant external-cause block, X46, X49 or T54.x depending on the substance, assigned alongside T32.74.

The dual-measurement structure is what makes corrosion documentation different from most of the code set. A single-sentence extent note is rarely enough. Structured wound assessment tools and burn flow sheets, which capture both metrics in separate fields, produce the records that survive review.

Where the claim actually stalls

A corrosion claim rarely fails at the point a payer reviews it. Three checkpoints upstream decide whether it pays on the first pass.

• At the encounter. The burn team records surface area and depth. If the depth figure never gets written down, the fifth character cannot be assigned and the chart goes back for a query, usually days later.
• At coding. T32.74 is grouped with its site code and external-cause code. A lone extent code gets rejected on an edit rather than adjudicated, so nobody reviews the clinical detail at all.
• At the clearinghouse. Format and eligibility edits run here, and a corrosion claim with no chemical named will sail through them. It then fails at the payer, which costs a full cycle instead of a same-day fix.

That third checkpoint is what a clean claim rate measures. Switching clearinghouses will not move it. Every element on the list above starts in the clinical record, so the chemical has to be caught while the chart is still open.

How Pabau keeps corrosion coding tied to the record

A corrosion case often lives in three places at once. The burn flow sheet sits in the chart. The codes sit in a lookup tool or a spreadsheet. The claim gets typed into a third screen. Every hop is a chance to lose the third-degree figure.

Practice management software like Pabau treats this as a records problem rather than a billing one. Its claims management workspace pre-fills the claim from the encounter record, so patient, provider and visit details carry across untyped. A built-in code lookup library then lets the coder find T32.74 and its neighbors without leaving the claim.

Required-field checks hold the claim until the record is complete. The coder sees an empty field while the chart is still open, rather than reading about it on a remittance advice three weeks on. For a burn unit running high-acuity cases, that difference is measured in whole billing cycles.

Keep corrosion coding attached to the record

Pabau pre-fills claims from the encounter record and keeps an ICD-10 code library on the same screen. Coders work T32.74 cases without switching systems.

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Conclusion

T32.74 is rarely the whole answer. A corrosion covering 70-79% of body surface with 40-49% full thickness needs the extent code. It also needs at least one anatomic-site code, plus an external-cause code naming the chemical. Assemble that set at the encounter and the claim usually clears on the first pass.

The habit worth forming is narrow. Ask the clinical team for two numbers rather than one, and ask while the chart is still open. Retrofitting a third-degree percentage weeks later rarely works, and an auditor can see the retrofit.

Coding accuracy on cases like this depends less on the code book than on where the documentation lives. Book a demo to see a corrosion case travel from encounter note to submitted claim without a second system in the way.

Continue your research

Need to understand how claims clear between the practice and the payer? Medical claims clearinghouse explains how electronic claim routing and validation works before reimbursement is issued.

Dealing with corrosion claim denials? Denial management in healthcare covers the most common denial reasons and the appeal workflows that resolve them fastest.

Want to verify insurance eligibility before the encounter? Insurance eligibility verification outlines real-time eligibility checks that confirm coverage before the patient arrives.

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