ICD code T31.31 – Burns involving 30-39% of body surface with 10-19% third degree burns

Key takeaways

ICD-10 code T31.31 is billable and valid for the 2026 ICD-10-CM edition, effective October 1, 2025. It covers 30-39% TBSA burns with a 10-19% third-degree component.

Sequence T20-T25 site codes first and report T31.31 as an additional code for the extent. Where the burn site is not documented, T31.31 can be the primary code.

T31.30 is not a zero-third-degree code. It covers the same TBSA band with a third-degree component of 9% or less.

Both the total burned percentage and the third-degree percentage must be documented in the clinical record. Most burn units use the rule of nines or the Lund-Browder chart.

Practice management software like Pabau keeps the burn note and the claim in one record, so coders can confirm the TBSA figures before submission.

ICD-10 code T31.31 is billable and valid for the 2026 code year

ICD-10 code T31.31 is a billable, specific ICD-10-CM diagnosis code for burns involving 30 to 39 percent of total body surface area.

Within that total, 10 to 19 percent of the body surface has sustained third-degree (full-thickness) burns. The 2026 edition of ICD-10-CM took effect on October 1, 2025, and T31.31 carries into the current code year unchanged.

The code belongs to the T31 category, which classifies burns by the extent of body surface involved rather than by anatomical location.

So T31.31 tells a payer how much of the body was burned and how severe the deepest burns were. Location, such as face, trunk, hand, or lower limb, is captured separately through T20-T25 codes. Those site codes are sequenced ahead of T31.31 whenever the record names the burn sites.

You can verify current billable status and code hierarchy using the CDC/NCHS ICD-10-CM web tool, which mirrors the official tabular list updated each October.

The CMS ICD-10 codes page also publishes the annual update files and coding guidelines used by Medicare and Medicaid payers.

Burns involving 30-39% of body surface are major burn injuries

Burns involving 30-39% of body surface count as a major burn injury by any clinical definition. The American Burn Association treats burns covering more than 20 percent TBSA in adults as major burns requiring burn center care. A T31.31 patient is therefore in the middle of a serious acute injury.

Within that 30-39 percent range, T31.31 specifies that 10 to 19 percent of the body surface has sustained third-degree burns.

The remainder, between 11 and 29 percentage points of total burn area, may be first or second degree. That layered specificity is what separates T31.31 from its siblings in the T31.3 subcategory.

• 30-39% TBSA: the total burned area, spanning all depths and body regions combined
• 10-19% third degree: the full-thickness component within that total, the part that has destroyed all skin layers
• Remaining burn area: may be first or second degree; the code does not further specify depth of the non-third-degree portion
• Clinical significance: third-degree burns in this range often require grafting and extended inpatient stays, driving higher DRG weights and inpatient reimbursement levels

The same dual-specificity logic runs through other traumatic injury codes. A primary descriptor captures the broad clinical fact, then a second numeric qualifier narrows the severity. With T31.31, both percentages have to appear in the physician’s note for the code to survive an audit.

TBSA comes from the rule of nines or the Lund-Browder chart

TBSA for burn coding is calculated with one of two validated methods. The rule of nines covers adults, and the Lund-Browder chart is used for pediatric patients or when greater anatomical precision is needed.

ICD-10-CM Official Guidelines do not mandate one over the other. The clinical record does have to document which method was used and the percentages it produced.

The rule of nines splits the adult body into 9 percent blocks

The rule of nines divides the adult body into regions that each represent 9 percent of total surface area, or a multiple of it. The head and neck account for 9 percent, and so does each arm. The anterior trunk is 18 percent, the posterior trunk another 18 percent, and each leg 18 percent. The perineum is 1 percent.

Work a case through it. An adult with burns across the anterior trunk (18%) and one arm (9%) reaches 27 percent, which sits below the T31.31 threshold.

Add the second arm at 9 percent and the total climbs to 36 percent, inside the 30-39 percent band. Adding the posterior trunk instead would take the same patient to 45 percent, which is T31.4x territory rather than T31.3x.

The Lund-Browder chart corrects for a child’s proportions

The Lund-Browder chart adjusts surface area percentages for age. It recognizes that a child’s head is proportionally larger, and each leg proportionally smaller, than an adult’s.

For pediatric burn admissions coded under T31.31, the chart should be the primary documentation tool. Applying the adult rule of nines to a 5-year-old underestimates head area and overestimates leg area. That error can drop the coder into the wrong TBSA tier.

For billing purposes, the physician or advanced practice provider has to state the TBSA percentage and the third-degree percentage in the clinical note. “Extensive burns” or “large burns” without numeric documentation does not support T31.31.

Practices working in software that tracks claims beside the clinical note can settle that question before the claim leaves the building.

The fifth character of T31.31 carries the third-degree tier

T31 runs from T31.0, burns involving less than 10% of body surface, through T31.9, burns involving 90% or more. Each subcategory covers a 10-point band of total burned surface.

The fifth character records how much of that total is third degree, and it never exceeds the band itself. T31.3 therefore subdivides into T31.30 through T31.33 only, and no T31.34 exists.

Each step up in the third-degree tier reflects greater full-thickness involvement, and usually a heavier resource burden for the care team. Payers and DRG groupers read that percentage directly off the fifth character. Selecting T31.30 when the documentation supports T31.31 is a coding error and an under-billing error at once.

Laid out on one scale, the four bands sit end to end like this.

The AAPC ICD-10-CM lookup lets coders cross-reference the full T31 hierarchy quickly when they are working through a complex burn case.

The 10-19% is measured against the whole body, not the burn

Third-degree burns, also called full-thickness burns, destroy the epidermis and the entire dermis, often reaching subcutaneous tissue. In T31.31, the 10-19% figure specifies that this destruction covers between one-tenth and just under one-fifth of the patient’s total body surface area. The denominator is the whole body, never the burned area alone.

That denominator trips up newer coders. Take a patient with 35% TBSA burns where 15% of the burned area is full thickness. At a glance that reads as 15% third degree.

But T31 coding requires the third-degree percentage relative to total body surface, so 15% of 35% works out at roughly 5.25% of the body. That case belongs in T31.30, not T31.31.

Physicians who write “15% full-thickness of the burn area” without naming the reference point leave the coder with an ambiguity. Clarifying the denominator is one of the most useful coaching points a coding team can take to a burn unit. One sentence in the note prevents a tier error that an auditor will find later.

T20-T25 site codes lead the claim when the record names a site

The tabular list note under category T31 sets the rule in two halves. T31 is the primary code only when the site of the burn is unspecified. Where the site is documented, T31 is used as a supplementary code with categories T20-T25.

Section I.C.19.d.6 of the ICD-10-CM Official Guidelines adds a second trigger for the category. T31 is assigned for acute burns when the site is not specified, or when there is a need for additional data. Reporting it alongside site codes is described there as advisable rather than mandatory.

The guideline points most strongly at third-degree burns covering 20% or more of body surface. T31.31 sits below that threshold, so the site codes carry the sequencing and T31.31 carries the extent.

Site codes first, then T31.31, then the external cause codes

When the record names the burn sites, the claim is built in this order:

1. First: assign the anatomical site code(s) from T20-T25 that describe the burn location(s) and depth. For example, T22.311A (burn of third degree of right forearm, initial encounter) or T21.31XA (burn of third degree of chest wall, initial encounter).
2. Second: assign T31.31 as an additional code to capture the total extent, 30-39% TBSA with 10-19% third degree.
3. Third: assign any external cause codes (place of occurrence, activity, status) as required by the guidelines.

If the record documents the extent but never names a site, that order collapses to one step. T31.31 is reported as the principal or first-listed diagnosis, followed by the external cause codes, and the claim is complete without a T20-T25 code.

No payer edit rejects T31.31 when it arrives alone

No Medicare Code Editor rule, NCCI edit, or published clearinghouse edit rejects a claim because T31.31 arrives on its own. T31.31 is a valid principal diagnosis and groups to a burn MS-DRG by itself. Site codes earn their place through clinical completeness and accurate DRG assignment, not through a payer edit waiting to fire.

Submitting the T20-T25 codes without T31.31 is compliant for outpatient encounters. On an inpatient burn admission it costs the record its severity detail, which feeds both DRG assignment and burn center resource tracking.

What the burn note must say before T31.31 holds up

A claim carrying T31.31 has to be supported by a clinical record that documents all of the following. A missing element gives a payer auditor grounds to deny or downcode the claim.

• Total TBSA percentage: a numeric value confirming the burn covers 30-39% of total body surface. “Extensive burns” is not sufficient.
• Third-degree percentage: a numeric value confirming the full-thickness component is 10-19% of total body surface, not of the burned area.
• Assessment method used: documentation of whether the rule of nines or the Lund-Browder chart was applied. Some payers request this for burn center audits.
• Burn depth by site: each anatomically coded site should note the depth (first, second, or third degree) so the third-degree percentage calculation is traceable.
• Burn sites, where they are known: named locations let the T20-T25 codes lead the claim. A record that never identifies a site is what makes T31.31 the primary code.
• Encounter type: T31.31 is used across all encounter types (initial, subsequent, sequela), while the anatomical T20-T25 codes carry the 7th character specifying encounter type.

Burn documentation queries are among the most common physician query scenarios in inpatient facilities. Compliance programs for burn units usually keep a standing query template for TBSA confirmation when the note is ambiguous.

The goal is specificity without leading the physician. Ask “what was the total TBSA, and what percentage was full thickness?” rather than “does the patient have T31.31?”

Four errors cause most T31.31 denials and downcodes

Four errors do most of the damage on burn claims. Each one is worth a standing check before the claim goes out.

• Leaving documented burn sites uncoded: when the record names the burn locations, the T20-T25 codes belong on the claim ahead of T31.31. The claim will not bounce for the omission, but it understates injury severity and can cost the case its DRG weight.
• Wrong third-degree tier: the third-degree percentage gets read as a proportion of the burn area rather than total body surface. That miscalculation puts the coder in the wrong subcategory. T31.30 (0-9% third degree) and T31.32 (20-29% third degree) are the usual mis-selections.
• Using an outdated code year: ICD-10-CM updates take effect October 1 each year. Claims dated on or after October 1, 2025 must use the 2026 code set. A pre-2026 descriptor format can trigger code-year edit failures at payers running automated validity checks.
• Missing TBSA documentation: submitting T31.31 when the note reads “large burns to trunk and arms”, with no numeric TBSA value, is coding without documentation. On audit that ends in code removal and a possible repayment demand. Query the physician before billing, not after a RAC letter arrives.

Practices that review burn claims before submission catch most of these at the front end. A few minutes of coder time costs far less than a post-payment audit finding on a burn case. Measuring the file against clean claim standards gives the team something concrete to validate before anything is transmitted.

Two documented numbers decide which T31.3 code you submit

Selecting the correct T31.3 sibling takes two confirmed figures from the clinical record: total TBSA and third-degree TBSA. Neither can be inferred or estimated for coding purposes. The table below maps the full T31.3 series, so coders can confirm the selection before submission.

Where the documentation does not clearly separate the tiers, query the provider before coding. A note reading “approximately 30% third-degree component” is one example. It never says whether that figure is of the burn area or of total body surface. Coding down to T31.30 to avoid the query is downcoding, and it carries its own compliance risk.

The ICD List free lookup tool helps coders cross-check the T31 subcategory tree while they review the documentation.

The sibling codes in the T31.3 series sit beside T31.31 in Pabau’s ICD-10-CM code library. Pulling up the neighboring tier is a quick way to settle a borderline case.

How Pabau keeps burn claims moving from note to payer

Burn cases generate documentation across several encounters, and the coder is usually reading a note written by someone else. When the TBSA figures sit in one system and the claim is built in another, confirming a percentage means opening both. The two versions do not always agree.

Pabau, practice management software built for healthcare practices, keeps the clinical record and the claim in the same place. Charting templates capture the TBSA percentage, the third-degree percentage, and the assessment method while the patient is still in front of the clinician.

Claim forms are then pre-filled from that record, with ICD-10-CM and CPT lookup libraries behind a search icon on the claim itself.

Claims go out through an integrated clearinghouse, and eligibility checks, remittance posting and claim-status updates return to the same patient file. Coders can check the burn note against the claim without switching systems, and billing leads can see which burn claims stalled and why.

Streamline burn case billing from documentation to clean claim

Pabau keeps burn documentation and the claim it supports in one record. The claim form is pre-filled from that record. Every submission is tracked through to remittance, so your team can see where a burn claim stands.

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Conclusion

T31.31 carries real reimbursement weight on burn cases, and the mistakes behind its denials are predictable.

The tier gets chosen from a percentage measured against the burn area instead of total body surface. The TBSA figure arrives as “extensive burns” rather than a number. Documented burn sites never reach the claim, which understates severity even though the claim still processes. Consistent pre-submission review catches all three.

Treat the two percentages as the code’s real content, and the rest of the burn claim follows. Pabau pre-fills the claim from the clinical record, checks that claim-required fields are complete before submission, and tracks each claim through to remittance. To see how that fits your burn coding workflow, book a demo.

Continue your research

Need to understand how clearinghouse edits catch burn code errors before submission? How a medical claims clearinghouse works explains the validation layer between your practice and the payer.

Want to reduce denial rates across your ICD-10 claims? Denial management in healthcare covers how to catch and correct claim errors before and after submission.

Looking for the billing document behind an accurate code set? What is a superbill walks through the structure that supports accurate ICD-10 code submission.

New to the revenue side of trauma and burn cases? What is medical billing sets out how a claim travels from the clinical note to payment.

Building a query and audit process around burn documentation? Medical billing compliance covers the controls that keep coded claims defensible on audit.

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