ICD code T31.43 – Burns With 30–39% Third-Degree Injury

Key takeaways

T31.43 reports burns covering 40-49% of total body surface area (TBSA), with 30-39% of TBSA being third-degree (full-thickness).

Both figures are percentages of the whole body, so the third-degree figure can never exceed the total burned figure.

The physician must document total TBSA and third-degree TBSA as separate numbers before T31.43 can be assigned.

T31.43 covers thermal burns only, and corrosions from chemicals are reported with T32.43 instead.

Pabau, the practice management platform we build, pre-fills claims from codes already on the patient record and submits them through Claim.MD.

ICD-10 Code T31.43: Quick reference and code details

ICD-10 Code T31.43 reports burns covering 40-49% of total body surface area (TBSA), with 30-39% of TBSA third-degree. It is a valid, billable ICD-10-CM code in the FY2027 code set, which runs from October 1, 2026, to September 30, 2027.

What T31.43 means: Decoding the code structure

T31.43 combines two measurements, and both are percentages of the patient’s total body surface area. Each character after the category carries one of them.

• T31: Burns classified according to extent of body surface involved, rather than by anatomic site
• .4 (4th character): 40-49% of total body surface area is burned, at any depth
• 3 (5th character): 30-39% of total body surface area is third-degree (full-thickness)

The fifth character measures third-degree burns against the whole body, not against the burned area. A patient with 45% TBSA burned, of which 35% TBSA is full-thickness, receives T31.43. A patient with 45% TBSA burned and 15% TBSA full-thickness receives T31.41 instead. The chart below lines up all five T31.4 depth bands on the same whole-body scale.

Because both figures share the same denominator, the third-degree band can never exceed the total band. That is why the T31.4 subcategory stops at T31.44, where third-degree burns reach 40-49% of TBSA.

Burn notes sometimes describe depth as a share of the wound, such as “about 75% of the burn is full-thickness.” That phrasing is not a TBSA figure. On a 45% burn it works out to roughly 34% TBSA, but the coder should not do the conversion. Query the physician for the third-degree extent as a percentage of TBSA.

Understanding the T31 burn code series

Category T31 runs from T31.0 through T31.99. T31.0 covers burns of less than 10% of body surface and takes no fifth character. T31.99 covers burns of 90% or more of body surface with 90% or more third-degree.

T31.4 is the fifth TBSA band, after T31.0, T31.1, T31.2 and T31.3. Within it, T31.43 is the fourth of five codes, one for each third-degree band from 0-9% to 40-49%.

T31 differs from the T20-T25 codes, which classify burns by anatomic site and depth. T32 is the parallel series for corrosions, so T31.43 is never used for chemical burns. Confirm whether the injury was thermal (T31) or chemical (T32) before assigning any extent code.

How total body surface area is calculated for T31.43

Burn teams estimate TBSA with the Rule of Nines for adults and the Lund-Browder chart for children. The coder takes the result from the physician’s note and never calculates it.

The Rule of Nines divides the adult body into regions worth 9% or a multiple of 9%. Head and neck account for 9%, each arm 9%, each leg 18%, the anterior trunk 18%, the posterior trunk 18%, and the perineum 1%.

A burn spanning the anterior trunk and both legs covers 18% + 36% = 54% TBSA, which already sits above the T31.4 band.

Burn teams adjust these percentages for infants and children, whose heads are proportionately larger, so use the physician’s documented TBSA figures rather than recalculating.

To support T31.43, the physician documents two figures, and both are percentages of total body surface area. The total burned area must fall between 40% and 49%. The full-thickness area must fall between 30% and 39% of TBSA. Both figures must appear explicitly in the medical record.

T31.43 vs. adjacent codes: Avoiding common confusion

The codes surrounding T31.43 are the most frequent source of miscoding. Each neighbor differs on one axis, either total TBSA or third-degree TBSA, often by a few percentage points.

When to use T31.43 vs. site-specific burn codes (T20-T25)

T31 codes serve a different purpose than T20-T25. Under ICD-10-CM Official Guidelines Section I.C.19.d.6, T31 is used when the burn site is not specified or when extra data is needed. With documented sites, the T20-T25 codes come first and T31.43 is added to report extent.

The guidelines also advise adding a T31 code when third-degree burns involve 20% or more of body surface. Every T31.43 case meets that threshold, since its third-degree extent is at least 30% of TBSA.

• T31.43 as additional code: A patient is admitted with third-degree burns of the chest wall (T21.31XA) and of multiple sites of both legs (T24.391A, T24.392A). T31.43 is added to report extent
• T31.43 as first-listed code: Documentation states “extensive burns, sites not specified, 45% TBSA with 35% TBSA third-degree”
• T31.43 never for corrosions: Chemical burns take T32.43, corrosions involving 40-49% of body surface with 30-39% third degree corrosion

Documentation requirements for T31.43

Incomplete documentation is a leading reason T31.43 claims are denied or downgraded. The medical record should contain the five elements below before the code is assigned.

• Total TBSA percentage: An explicit numeric statement that the total burned area is 40-49% of body surface
• Third-degree TBSA percentage: An explicit numeric statement that full-thickness burns cover 30-39% of total body surface area, not a share of the burned area
• Assessment method: The tool used, such as the Rule of Nines or a Lund-Browder chart
• Burn depth by region: The treating clinician’s depth notation for each affected body region, which also supports the T20-T25 codes
• Clinician signature: Signed documentation from the physician or qualified healthcare professional managing the burn

Query the treating physician when the record gives total TBSA but omits the third-degree extent. A note stating “45% TBSA burn” alone does not support T31.43. Do not default to T31.40 in that case. T31.40 states that third-degree burns cover 0-9% of TBSA, so it misreports extent when deeper burns are charted.

Coding guidelines and official instructions for T31.43

ICD-10-CM Official Guidelines Section I.C.19.d governs burn and corrosion coding. These provisions apply directly to T31.43.

• Sequencing rule: When more than one burn is present, sequence first the code for the highest degree of burn. T31.43 follows the T20-T25 site codes when sites are documented
• Burns vs. corrosions: Corrosions are classified to T32, so never assign T31.43 for a chemical burn, whatever TBSA is documented
• External cause codes: Add an external cause code for the source, intent and place of the burn. X00-X08 covers exposure to smoke, fire and flames
• Infection codes: For any documented infected burn site, add a code for the infection. T31.43 does not capture infection by itself
• No 7th character: T31.43 takes no 7th character. The encounter type is carried by the T20-T25 site codes, which use A, D or S

Common payer requirements and prior authorization considerations

A burn of this size meets American Burn Association criteria for burn center referral. Those criteria include partial-thickness burns over 10% of TBSA and any full-thickness burn. Expect payers to require authorization for inpatient burn care and for surgery such as skin grafting.

• Inpatient admission justification: Payers require documented medical necessity for inpatient admission. A 40-49% TBSA burn with extensive full-thickness involvement usually meets admission criteria, but the note must state the acuity explicitly
• Burn center transfer: Document the receiving facility, date and medical necessity when a patient is transferred to a burn center. Claims without transfer documentation are often denied
• Skin graft prior authorization: Many payers require authorization for skin grafting, such as split-thickness autografts (CPT 15100-15101 and 15120-15121). Verify with the payer before a scheduled procedure
• Medical necessity narrative: Some payers ask for an attached clinical narrative on high-cost claims, and T31.43 claims with grafting codes often qualify

Requirements differ by plan and contract year. Elective burn reconstruction usually needs its own authorization, separate from the acute admission.

Top claim denial reasons for T31.43 and how to prevent them

The five denial causes below recur on T31.43 claims, and a coder can catch each one before submission. Applied to burn claims, denial management in healthcare starts with these checks.

Practices with high burn-claim volumes should keep a list of medical billing denial codes to hand. The CARC on each remittance tells the billing team which of the five causes to correct before resubmitting. The clean claim submission requirements for burn cases include both TBSA figures, correct sequencing and any prior authorization number.

CPT codes commonly reported with T31.43

T31.43 is a diagnosis code, so the claim pairs it with procedure codes for the burn care delivered. Grafting usually drives the claim value, and CPT 15100 is the base code for split-thickness autografts on the trunk, arms and legs. Verify NCCI edits and any LCD or NCD before submitting a combination, because rules for burn procedures vary by payer.

Build an authorization check into your revenue cycle management workflow before T31.43 claims with grafting codes go out. These encounters carry high claim values, so a missing authorization is costly.

How Pabau supports accurate T31.43 claims

Burn claims at this extent pass through several hands, and the two TBSA figures have to survive each handoff. When coders re-key diagnosis codes into a separate billing system, a T31.41 can become a T31.43 by accident.

Pabau keeps the treatment record and the claim in one system. Its claims management software pre-fills the claim from the diagnosis and procedure codes already on the patient record. In the US, it then submits and tracks the claim through the Claim.MD clearinghouse, with real-time eligibility checks.

The result is fewer keying errors between chart and claim, and a clear status trail when a payer asks for documentation. Medical billing compliance on burn cases depends on both correct codes and a submission pathway you can audit.

Keep burn claims consistent with the chart

Pabau pre-fills claims from the codes on the patient record and submits them through Claim.MD. Your T31.43 claims match the documentation that supports them.

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Conclusion

Assign T31.43 only when the note states both figures as percentages of total body surface. When depth arrives as a share of the wound, or not at all, a physician query costs less than a corrected claim.

Getting this right protects more than one claim. Burn units and payers use the extent code to judge injury severity, so a wrong fifth character misstates how badly the patient was burned.

Pabau’s Claim.MD clearinghouse integration submits and tracks burn claims built from the codes on the patient record. Book a demo to see how Pabau keeps your burn claims in step with the chart.

Continue your research

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