ICD code T31.73 – Large burn injury 70-79% body surface area

Key takeaways

T31.73 applies when burns cover 70-79% of body surface and third-degree burns cover 30-39% of it.

Both percentages must appear in physician documentation. A single TBSA figure with no depth breakdown will not support T31.73.

Valid seventh characters are A (initial encounter), D (subsequent encounter), and S (sequela) only.

Site-specific burn codes (T20-T25) and external cause codes must be coded alongside T31.73.

Practice management software like Pabau handles ICD-10 workflows and electronic claim submission for burn billing.

ICD-10 Code T31.73: Definition and code-level details

ICD-10 Code T31.73 is a fully specified, billable ICD-10-CM code valid for FY2026 claims.

Its official descriptor reads Burns involving 70-79% of body surface with 30-39% third degree burns. The code sits in Chapter 19 of the ICD-10-CM Tabular List, which covers injury, poisoning and certain other consequences of external causes.

It belongs to the T31 category, which classifies burns by the percentage of body surface involved rather than by anatomical site. You can verify current-year billability using the CDC/NCHS ICD-10-CM web tool.

T31 codes are additive to the site-specific burn codes in categories T20 through T25, never a replacement for them. Coding T31.73 alone, with no companion site code, is one of the most common reasons these claims come back denied.

Code description and clinical meaning

T31.73 encodes two distinct clinical measurements on a single claim line. The first axis is total body surface area. Burn injury of any depth must affect 70 to 79 percent of the patient’s body surface for this code to apply.

The second axis is burn depth. Of the patient’s total body surface, 30 to 39 percent must carry third-degree burns. Full-thickness burns destroy both the epidermis and the dermis, and they often extend into subcutaneous tissue. Both figures carry equal weight in code selection.

Third-degree burns are clinically distinct. Skin appears white, brown, or charred. Sensation is absent because nerve endings are destroyed, and spontaneous healing without grafting is not possible. Documenting depth per body region is therefore both a clinical necessity and a coding requirement.

TBSA calculation methods accepted for T31.73

Two methods are accepted for estimating TBSA, and physicians must name the method used in the record.

• Rule of Nines: assigns 9% each to the head, each arm, the chest, the abdomen, and the upper back. The lower back, each thigh, and each lower leg take 9% each as well. The perineum accounts for the remaining 1%. At 70% TBSA, roughly seven anatomical segments are fully involved.
• Lund and Browder chart: more precise for children, because it adjusts head and thigh percentages by age. Burn center payers often require it for pediatric burns as evidence of methodical assessment.

Neither method is mandated by ICD-10-CM. The physician record must still document which one was used, the percentage arrived at, and the breakdown by depth. A chart note reading only “extensive burns” cannot support T31.73.

Where T31.73 sits in the T31.7x code series

The T31.7x sub-category covers every burn in the 70 to 79 percent TBSA band. Eight sibling codes share that first-axis value, and the only differentiator is the third-degree sub-percentage. Selecting the wrong sibling is the most common specificity error in this band.

How to assign T31.73 correctly

Correct assignment of ICD-10 Code T31.73 follows five sequential steps. Skipping one is where claims fail, particularly on payer audits for high-acuity burn admissions. The CMS ICD-10 codes page publishes updated tabular instructions and coding guidelines each fiscal year.

1. Confirm TBSA falls in the 70-79% range. Review the physician’s burn diagram or narrative. The documented percentage must be at least 70% and no greater than 79%. A figure of 80% pushes the code to the T31.8x band.
2. Calculate the third-degree sub-percentage. The physician must separately state what portion of the body is full-thickness. For T31.73, that figure falls between 30% and 39% of total body surface. It is not 30-39% of the burned area alone.
3. Verify documentation supports both figures explicitly. Implicit statements such as “most of the burn was deep” do not meet specificity requirements. The record must carry discrete numeric percentages for each depth tier. It must also name the calculation method, either Rule of Nines or Lund-Browder.
4. Select the correct seventh character. T31.73 takes a seventh character after a placeholder X: T31.73XA (initial encounter), T31.73XD (subsequent encounter), or T31.73XS (sequela). The X is mandatory, because T31.73 has only five characters before the seventh-character position.
5. Identify all required companion codes. T31.73 is never a standalone code on a complete claim. Add site-specific burn codes, external cause codes, and any inhalation injury codes per the ICD-10-CM tabular instructions.

Seventh character options for T31.73

Required additional codes with T31.73

The ICD-10-CM tabular list instructs coders to use additional codes alongside T31.73. Submitting the TBSA code without its companions leaves the claim incomplete and exposed on audit.

• Site-specific burn codes (T20-T25): Required for each anatomical region burned. T31.73 documents extent, while the T20-T25 codes document site and depth at the location level. Both sets belong on the claim.
• External cause codes (X00-X19): Identify the cause of the burn, such as flame, scald, chemical, electrical, or radiation. The ICD-10-CM Official Guidelines for Coding and Reporting require external cause coding for Chapter 19 injury codes wherever possible.
• Place of occurrence (Y92): Documents where the burn happened. Payers increasingly validate that external cause and place of occurrence codes are present on high-severity burn admissions.
• Inhalation injury (T59.-, J70.5): Code separately when documented. Inhalation injury frequently accompanies large TBSA burns from enclosed-space fires, and it carries its own reimbursement weight.
• Sepsis (A41.-, A40.-): Code if documented, because sepsis is a common complication with burns over 70% TBSA and substantially affects DRG assignment.

T31.73 vs adjacent codes: How to tell them apart

The three most common wrong-code selections around T31.73 involve one step in the wrong direction, on either the TBSA axis or the third-degree axis. The map below plots each neighbour against the figure that separates it from T31.73.

The table sets out the same four neighbours with the documentation detail that separates each one. Use AAPC’s ICD-10-CM lookup to cross-reference sibling codes when documentation falls near a boundary.

T31 vs T30: When to use each

T30 (burn of body surface, site unspecified) is appropriate only when documentation genuinely lacks enough information to assign a more specific code. T31.73 requires explicit numeric documentation of both TBSA and third-degree sub-percentage. If those figures are absent, query the physician before defaulting to T30.

Querying is always preferable. Unspecified codes attract payer scrutiny, and they may not support inpatient admission medical necessity for a burn injury of this severity.

Documentation requirements for a valid T31.73 claim

T31.73 claims are high-value, and auditors treat them accordingly. Payers look for specific documentation elements, and a missing element is a preventable denial. The wider rules on medical billing compliance apply to every inpatient claim at this level of acuity.

• Explicit TBSA percentage in the 70-79% range — a number, not a descriptor such as “extensive” or “massive”
• Explicit third-degree sub-percentage in the 30-39% range — stated as a percentage of total body surface, not of the burned area
• TBSA calculation method named — Rule of Nines or Lund-Browder, with Lund-Browder documented for pediatric patients
• Burn depth documented per region — the record must show which anatomical areas carry the third-degree component. That supports both the TBSA code and the site-specific T20-T25 codes
• Encounter classification — initial, subsequent, or sequela, matching the seventh character selected
• External cause — the mechanism, such as flame, scald, chemical or electrical, plus the place of occurrence
• Inhalation injury notation — present or absent must be documented, and “patient denies” is acceptable if it appears explicitly

AHA Coding Clinic guidance emphasizes that TBSA documentation must reflect the physician’s assessment at the time of the encounter. A retrospective estimate does not qualify. Burn wounds evolve, so depth percentages documented on day one may differ from those recorded on day three. Each encounter stands on its own documentation.

Payer requirements and prior authorization

Burns involving 70 to 79 percent TBSA usually require inpatient admission, often at a designated burn center. Most major payers treat this as presumptive medical necessity for inpatient level of care. Prior authorization is still a processing requirement for commercial plans and some Medicare Advantage products.

Facilities billing T31.73 should obtain authorization before or at the time of transfer to a burn center, rather than relying on retrospective approval. Medicare fee-for-service does not require prior authorization for inpatient hospital admissions, but post-payment audits for high-severity burn DRGs are common.

The supporting clinical documentation must include the burn center assessment, daily wound care notes, and operative reports for any debridement or grafting performed.

Common claim denials and how to avoid them

T31.73 claims get denied for two broad reasons: specificity errors in the code itself, and documentation that never reached the record. Most are preventable. Building code-specific denial rules into billing review catches them before submission.

Every denial comes back with a CARC code attached to the remittance. The denial codes reference explains the ones payers return most often on complex inpatient claims, and what each one asks you to correct.

Coding for burn-related procedures alongside T31.73

T31.73 is a diagnosis code. Procedure coding for burn-related interventions is separate, using ICD-10-PCS for inpatient work and CPT for outpatient or professional billing. The diagnosis and the procedure codes must align clinically. A skin graft CPT code submitted with a low-acuity burn diagnosis triggers a clinical logic edit.

Common procedures associated with 70-79% TBSA burns and their coding context:

• Debridement: Non-excisional debridement (CPT 97597, 97598) and excisional debridement (CPT 11042-11047) are frequently performed in the first days after admission. Each session must align with documented wound size and depth.
• Split-thickness skin graft (STSG): CPT codes 15100-15101 apply to the recipient site, and donor site closure is coded separately. Autograft in a patient with 70-79% TBSA typically requires several operative sessions.
• Temporary biological coverage (allograft/xenograft): CPT 15271-15278 cover the application of skin substitute grafts while the patient is stabilized for definitive grafting. These are coded alongside T31.73XA during the active treatment phase.
• Escharotomy: CPT 16035-16036 when performed for compartment syndrome, or to restore circulation to a burned extremity. The documented clinical indication must support the code.

ICD-10-PCS is used for inpatient procedure coding. Burn surgeons and coding teams at burn centers typically work closely. Operative reports then carry the detail ICD-10-PCS requires for root operation, body part, and approach specificity.

ICD-9-CM crosswalk for T31.73

Retrospective billing, legacy record review, and some payer crosswalk tools still reference ICD-9-CM codes. The transition from ICD-9 to ICD-10 took effect on October 1, 2015. Claims billed before that date used the ICD-9-CM code set, which structured burn coding differently.

For crosswalk work, map T31.73 against the CMS General Equivalence Mappings file. GEMs is the payer-approved reference for moving between the two code sets. Third-party crosswalk tools are useful for a first pass, but confirm every result against GEMs before it goes on a claim. ICD-10 gained far more burn-coding specificity by adding the dual-axis structure that T31.73 uses.

How Pabau keeps multi-code burn claims accurate

A burn admission coded to T31.73 rarely leaves the practice as a single line. The claim carries the TBSA code, site codes from T20-T25, an external cause code, a place of occurrence code, and often an inhalation injury code. Assembling that by hand, across several encounters, is where the figures start to drift apart.

Pabau is an all-in-one practice management system with software for billing teams built into it. Diagnosis codes attach to the encounter record that already holds the clinical note. The coder then builds the claim from the documentation rather than from memory.

Claims go out electronically to US payers, and the remittance advice comes back into the same record. Burn claims at this TBSA level often return remark codes tied to DRG assignment rather than to the code itself. Reading the remittance in context tells the billing team whether to correct a code or query the physician.

Streamline complex ICD-10 coding workflows

Pabau supports multi-code burn injury claims with built-in ICD-10 diagnosis code workflows, electronic claim submission, and real-time remittance processing. See how it fits your billing team.

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Conclusion

T31.73 rewards documentation discipline more than coding skill. Two percentages, a named calculation method, and the correct placeholder and seventh character all have to be in place. So does a full set of companion codes covering site, cause, and any inhalation injury.

Get one of those elements wrong and the claim shifts to a sibling code, comes back denied, or turns into an audit finding. The fix sits upstream. Query the physician while the patient is still in front of them, rather than reconstructing percentages weeks later from a chart.

Book a demo to see how Pabau assembles multi-code burn claims and tracks each one through to remittance.

Continue your research

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