ICD code T32.30 – Corrosions involving 30-39% of body surface

Key takeaways

T32.30 covers chemical corrosions of 30-39% of body surface where third-degree corrosion covers 0% to 9% of body surface.

The code follows the documented third-degree band, so 10-19% third degree moves the claim to T32.31, 20-29% to T32.32, and 30-39% to T32.33.

T32.30 is a billable ICD-10-CM code, usually reported as an additional code alongside site-specific corrosion codes from T20-T25.

Seventh characters A, D, and S belong to the T20-T25 site codes, because T32.30 takes no seventh character and is not used for sequelae.

Pabau’s claims management software keeps the clinical note, the codes, and the invoice for a corrosion claim in one patient record.

ICD-10 Code T32.30: Code definition and clinical scope

ICD-10 Code T32.30 is the billable ICD-10-CM code for corrosions involving 30-39% of body surface with 0% to 9% third degree corrosion. It sits in category T32, “Corrosions classified according to extent of body surface involved.” The code set is maintained by the Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics (NCHS).

Corrosions are burns caused by chemicals, such as acids, alkalis, and other caustic substances. ICD-10-CM codes them under the same rules as thermal burns, with their own corrosion subcodes.

Each character after the category does one job. The fourth character “3” places the injury in the 30-39% total body surface area (TBSA) band. The fifth character “0” records that third-degree corrosion covers 0% to 9% of body surface.

A patient with corrosions over 34% of body surface, and third-degree corrosion over 6% of body surface, maps to T32.30. The same patient with third-degree corrosion over 12% maps to T32.31.

Burn vs corrosion: How ICD-10-CM separates them

ICD-10-CM separates burns from corrosions by mechanism, but both share the same site categories. Thermal burns come from heat sources, electricity, or radiation. Corrosions are burns due to chemicals, whatever the temperature of the substance. Categories T20-T25 hold both, with separate burn and corrosion subcodes for each site.

Pairing a T31 extent code with a chemical injury mixes two classifications for one event. The extent code, the site codes, and the agent code should all describe the same chemical mechanism.

T32.3x subcodes: How the third-degree percentage picks the code

The T32.3- subcodes all cover corrosions of 30-39% TBSA. They differ only in how much of the body surface has third-degree (full-thickness) corrosion, so the coder selects by the documented third-degree band.

T32.30 is not reserved for injuries with no full-thickness damage. A note documenting third-degree corrosion over 5% of body surface still codes to T32.30. If the note gives a total TBSA but no third-degree percentage, query the clinician rather than assuming the 0% to 9% band.

How to calculate TBSA for T32.30 documentation

Accurate TBSA documentation is the prerequisite for any T32.3- code. The ICD-10-CM Official Guidelines for Coding and Reporting (Section I.C.19.d.6) state that categories T31 and T32 are based on the classic rule of nines. Providers may adjust those percentages for infants and children, whose heads are proportionately larger.

Rule of nines

The rule of nines assigns the head and neck 9%, each arm 9%, and each leg 18%. The anterior trunk and the posterior trunk count 18% each, and the genitalia 1%. For pediatric patients, clinicians often use a Lund-Browder chart, which adjusts head and leg proportions by age.

A corrosion covering the whole anterior trunk plus one arm equals 27% TBSA, which falls in the T32.2- band. Add part of the posterior trunk, and the total can reach the 30-39% band of T32.3-. From there, the third-degree share picks the fifth character, as the decision below shows.

What the coder needs from the clinical note

• An explicit TBSA percentage (e.g., “35% TBSA involvement”)
• The percentage of body surface with third-degree corrosion (e.g., “8% full thickness”)
• Identification of each affected body region, for the site-specific T20-T25 codes
• Depth assessment per region: First degree, second degree, or third degree
• The chemical agent and the intent, for the T51-T65 toxic effect code
• Encounter type (initial, subsequent, or sequela), for the seventh character on the T20-T25 site codes

When the clinician documents only “extensive burns” or “large chemical exposure” without percentages, T32.30 cannot be assigned. The coder must query the clinician before submitting.

Required additional codes with T32.30

T32.30 is an extent code. Under Section I.C.19.d.6 of the guidelines, T31 and T32 codes are assigned when the site is not specified or when additional data is needed. When sites are documented, T32.30 is reported alongside site-specific corrosion codes from T20-T25. Good medical billing workflows build this companion-code check into charge capture.

Site-specific companion codes (T20-T25)

Each documented site gets its own corrosion code, because the guidelines tell coders to assign separate codes for each burn site. A patient with corrosions of the trunk (T21.-), the upper limb (T22.-), and the lower limb (T24.-) carries all three alongside T32.30.

These site codes carry the seventh character. Use “A” for active treatment, “D” for routine care during the healing phase, and “S” for sequelae such as scar contracture. T32.30 has no seventh character, and T31 and T32 codes are not used for sequelae.

Agent and external cause codes

The T20-T25 corrosion subcodes carry a “code first” note pointing to T51-T65. That toxic effect code identifies the chemical and the intent, such as T54.2- for corrosive acids or T54.3- for corrosive alkalis. Its sixth character records intent, from accidental to assault. The site codes also instruct an additional Y92 code for place of occurrence.

ICD-10-CM sets no national requirement to report external cause codes unless a payer or state mandates it. Where they are reported, three code types complete the picture:

• Place of occurrence: Y92.- (where the exposure happened)
• Activity: Y93.- (what the patient was doing at the time)
• External cause status: Y99.- (e.g., civilian activity done for income or pay)

Sequencing rules: When T32.30 is principal vs additional diagnosis

Sequencing for corrosions follows ICD-10-CM Official Guideline Section I.C.19.d, which covers burns and corrosions. T31 and T32 codes serve as primary codes only when the site is not specified. When sites are documented, the site-specific corrosion codes lead and T32.30 follows as an additional code. Strong medical billing compliance processes keep these sequencing decisions documented and auditable.

Inpatient sequencing

1. The T51-T65 toxic effect code, per the “code first” note on the corrosion site codes
2. The site-specific corrosion code (T20-T25) for the highest degree, then the other sites
3. T32.30 as an additional code for extent
4. Y92 and any other external cause codes the payer requires
5. Any codes for complications or comorbidities that affect management

Outpatient sequencing

Outpatient encounters follow the same companion-code logic, with the reason for the visit listed first. A wound care visit for a healing corrosion lists the site-specific code with seventh character “D,” and T32.30 can follow for extent.

Adjacent codes commonly confused with T32.30

The T32.20 to T32.40 range generates most boundary errors. Each total-TBSA band spans ten percentage points, and so does each third-degree band. A loosely documented figure can shift the code by a full subcategory.

The T32.30 to T32.31 boundary is the most consequential, and it turns on one point: 9% versus 10% third degree. A note reading “about 10%” leaves the fifth character open, because 10% exactly belongs to T32.31. Confirm the exact percentage before choosing “0” or “1.”

Payer requirements and prior authorization for T32.30 claims

Corrosions covering 30-39% of body surface usually need inpatient care, often in a burn unit, so many payers review the admission. Pabau, the practice management platform we build, includes denial-reducing claims software. Its pre-submission documentation checks help avoid authorization delays.

Medicare and Medicaid

Medicare has no National Coverage Determination (NCD) specific to T32.30, so local contractor policies set the documentation expectations. The TBSA and third-degree percentages belong in the admitting physician’s note, not only in nursing documentation. Medicaid rules vary by state, so check the state program’s requirements for burn admissions.

Commercial payers

Commercial payers commonly ask for the following before authorizing an inpatient admission for T32.30:

• Documented TBSA and third-degree percentages with a clinical basis (rule of nines or Lund-Browder)
• Site-specific corrosion codes from T20-T25 on the authorization request
• Chemical agent identification, which maps to the T51-T65 code
• Burn unit or specialized care facility designation
• Attending physician certification of admission necessity

An authorization request that lists T32.30 without its site-specific companion codes commonly draws an initial denial. That holds even when the clinical documentation supports the claim.

Common claim denial reasons for T32.30

T32.30 denials cluster around a small set of recurring errors. Claims sent through Pabau’s Claim.MD integration pass a clearinghouse check, which catches some of these errors before the payer sees them. Understanding the denial management workflow for T32.30 helps prevent the rework that follows a rejected corrosion claim.

• Missing TBSA documentation: The clinical note does not state a specific percentage. The claim cannot support the 30-39% band.
• Wrong seventh character on the site codes: A T20-T25 site code carries “A” for a routine wound care visit that should carry “D.” Using “S” while the corrosion is still healing is the same error. T32.30 itself takes no seventh character.
• Missing site-specific companion codes: T32.30 submitted without T20-T25 site codes, when the note documents the sites, conflicts with the guidelines and invites rejection.
• Missing agent code: The T51-T65 toxic effect code required by the “code first” note is absent. A heat-source external cause code on a chemical injury causes the same mismatch.
• Wrong third-degree band (T32.30 vs T32.31): The note documents third-degree corrosion over 10% or more of body surface, but the claim carries T32.30. The reverse error overstates severity on audit.
• TBSA calculation inconsistency: The documented TBSA does not match the body regions listed in the note, which triggers medical necessity review.

Reviewing medical billing denial codes for corrosion-related rejections helps coding teams identify patterns across T32.30 claims before they become systemic billing problems.

Documentation checklist for T32.30

A clean claim submission for T32.30 depends on the clinical note capturing each element a coder needs. Use this checklist at the point of documentation, because missing details are harder to recover at charge entry.

• TBSA percentage explicitly stated (e.g., “34% TBSA involvement”) by the attending clinician
• Calculation basis noted (rule of nines or Lund-Browder chart, referenced or implied by a regional breakdown)
• Third-degree percentage stated as a share of body surface, so the coder can choose between 0% to 9% (T32.30) and 10-19% (T32.31)
• All affected anatomical sites identified for the site-specific companion codes (T20-T25)
• Chemical agent and intent identified (acid, alkali, specific caustic substance) for the T51-T65 code
• Encounter type clear (active treatment, healing phase, or sequela) for the seventh character on the T20-T25 site codes
• Place of occurrence documented for Y92, plus activity and status where the payer requires them

How claims management software prevents T32.30 denials

Most T32.30 errors start in the clinical note, long before a biller sees the claim. A missing third-degree figure or an unlisted site turns into a query, a resubmission, or a denial weeks later.

Pabau keeps the clinical note, the codes, and the invoice in one patient record. Billers can check the TBSA figures, the site codes, and the agent code against the note before the claim leaves the practice. Claims then go out electronically through the Claim.MD integration.

The result is fewer corrosion claims coming back for rework, and steadier payment for high-acuity burn care.

Simplify corrosion claim submissions

Pabau’s claims management tools help burn care teams check site codes, agent codes, and TBSA documentation before submission, so T32.30 claims go out complete. See how it works for your practice.

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Conclusion

T32.30 turns on two numbers in the note: a total TBSA of 30-39%, and third-degree corrosion under 10% of body surface. With both on record, the choice between T32.30 and T32.31 stops being a judgment call.

The stronger habit is to capture those figures at the bedside rather than chase them at charge entry. Pabau’s revenue cycle management tools help burn care and emergency teams keep those checks inside the clinical workflow. Book a demo to see how Pabau handles corrosion and burn claims end to end.

Continue your research

Need to understand clearinghouse submission for T32.30 and related corrosion claims? Claim.MD clearinghouse overview covers how electronic claim routing works for complex injury codes.

Want to see how 837P claim files handle multi-code corrosion submissions? 837 file format guide explains how companion codes and external cause codes are structured in electronic transactions.

Coding corrosion injuries alongside eligibility verification? Insurance eligibility verification outlines how pre-submission eligibility checks reduce denials for high-acuity burn care claims.

Third-degree corrosion at 10% or more? ICD-10 code T32.31 covers the next third-degree band within 30-39% of body surface.

Same extent, but a thermal burn? ICD-10 code T31.30 is the burn counterpart for 30-39% of body surface.

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