ICD code T31.77 – Burns involving 70-79% of body surface

Key takeaways

T31.77 is a billable ICD-10-CM code for burns covering 70-79% of body surface with 70-79% of body surface third-degree. Both percentages must be documented as numbers.

The T31 category works on two axes. The first digit after the decimal gives the total body surface burned, and the second gives the share of body surface that is third-degree.

T31.77 is complete as written and takes no seventh character — A, D or S goes on the T20-T25 site-specific burn codes reported alongside it.

Missing or inconsistent TBSA and third-degree percentages in the medical record are the first thing to check when a T31.77 claim is denied.

Pabau, the practice management and billing platform we build, files electronic CMS-1500 claims through Claim.MD for the physician side of burn care.

ICD-10 code T31.77: Quick reference and code details

ICD-10 code T31.77 is the billable ICD-10-CM code for burns covering 70-79% of body surface, with 70-79% of body surface third-degree.

It is valid for fiscal year 2026 under the CMS ICD-10-CM tabular list.

The code sits in Chapter 19 of the full ICD-10-CM code set, in category T31. That category classifies burns by the extent of body surface involved rather than by anatomical site.

How the T31 category works: Two percentages, one code

The T31 category sorts burn codes along two axes at once. The first axis is the total body surface burned, in 10% bands from under 10% (T31.0) to 90% or more (T31.9). The second axis is the percentage of total body surface that is third-degree, or full-thickness, in the same 10% bands.

Third-degree burns are part of the burned total, so their share can never exceed it. Each subcategory therefore stops at the band that matches its own total, and T31.7 ends at T31.77.

T31.77 sits where both axes reach 70-79%. The first digit after the decimal (7) is the burned total: 70-79% of body surface. The second digit (7) is the third-degree share: 70-79% of body surface is full-thickness. Both must be true at once, and both must be stated in the medical record. The chart shows the whole T31.7 subcategory on one scale.

The table lists each T31.7 code with the clinical picture it describes.

The most common error in this subcategory is assigning T31.70 when the physician documents extensive third-degree burns without a separate percentage. Without that figure, query the physician rather than default to T31.70. Defaulting understates injury severity and may suppress the appropriate DRG. The band also has to match exactly: 55% of body surface third-degree is T31.75, not T31.77.

Sequencing T31.77 with site-specific burn codes (T20-T25)

T31.77 is a complete code as written. Category T31 has no seventh-character extension, so T31.77A, T31.77D and T31.77S do not exist and are rejected as invalid codes.

The encounter type lives on the site-specific burn codes from categories T20-T25 instead. Each burned region gets its own code for site and depth, and each of those codes takes a seventh character.

Under the ICD-10-CM burn guidelines, sequence first the site code that reflects the highest degree of burn. Report T31.77 as an additional code to show the extent of body surface involved. A T31 code stands alone only when the burn site is not specified.

A common error is keeping the A character on the site codes after the acute phase ends. Once the patient moves to routine wound care or outpatient follow-up, the site codes switch to the D character. T31.77 itself never changes and never takes a seventh character.

TBSA calculation: How to determine the correct burn percentage for coding

Accurate TBSA calculation determines which T31 code applies. Two common clinical methods are used, and the American Burn Association (ABA) recognizes both: the Rule of Nines and the Lund-Browder chart.

Rule of Nines

The Rule of Nines divides the adult body into regions worth 9% of total body surface area, or a multiple of 9%:

• Head and neck: 9%
• Each arm: 9%
• Front of each leg: 9%, and back of each leg: 9%
• Front of the trunk: 18%, and back of the trunk: 18%
• Perineum: 1%

This method is fast and adequate for initial triage. It can misjudge burns in pediatric patients, whose heads are larger relative to body surface area. In a T31.77 case, the Rule of Nines will usually show burns across most of the trunk, both legs and both arms.

Lund-Browder chart

The Lund-Browder chart provides a more precise TBSA estimate by adjusting body region percentages based on patient age. It is the preferred method for pediatric burn patients. It also suits any case where the TBSA estimate drives major decisions, such as burn center transfer and fluid resuscitation.

For ICD-10-CM coding purposes, the method used to calculate TBSA is less important than what appears in the medical record. The physician must document both the total TBSA burned and the percentage of total body surface that is third-degree, each as a number. A notation that reads “extensive burns” or “major burns to trunk and extremities” is not sufficient for T31.77.

External cause codes to report with ICD-10 code T31.77

External cause codes are covered in Section I.C.20 of the ICD-10-CM Official Guidelines. There is no national mandate to report them, but they are recommended for burn injuries. Report them wherever a payer or state reporting rule requires them. A full set for a T31.77 case covers four categories.

Sequencing follows the ICD-10-CM burn guidelines. List the T20-T25 site codes first, starting with the highest degree of burn, then T31.77, then the external cause codes. External cause codes never serve as the principal diagnosis.

Common codes reported alongside T31.77

Burns covering 70-79% TBSA with extensive third-degree involvement almost always produce a complex, multi-code claim. These conditions and procedures are routinely coded alongside ICD-10 code T31.77 in burn center admissions.

Inhalation injury

Inhalation injury accompanies a significant proportion of major flame burns. For smoke inhalation, report T59.811A (toxic effect of smoke, accidental, initial encounter). T59.891A (toxic effect of other specified gases, fumes and vapors, accidental, initial encounter) applies when a different gas is documented. Burns of the respiratory tract itself take a code from T27.-.

Per AHA Coding Clinic guidance, inhalation injury codes sequence after the burn code when both are present.

Burn wound procedures

Surgical debridement and skin grafting are standard treatments for third-degree burns at this scale. Circumferential burns may need an escharotomy to relieve compartment pressure, coded in ICD-10-PCS as an incision of skin. Split-thickness skin grafts (STSG) are coded using ICD-10-PCS replacement codes specifying the body region, graft type, and qualifier. Each graft site requires its own procedure code, which affects DRG grouping and reimbursement significantly.

MS-DRG mapping

T31.77 cases typically map to burn DRGs 927-935 under the CMS MS-DRG system. The exact DRG depends on whether an operating room procedure was performed and whether complications or comorbidities (CC/MCC) are present. DRG groupings change every year, so check the current fiscal year grouper before estimating reimbursement.

Documentation requirements to support a T31.77 diagnosis

Payers reviewing T31.77 claims look for specific numbers in the medical record. Narrative descriptions of burn severity are not enough, because coders assign T31 codes only from the percentages the physician states. A clean claim for this code starts with complete documentation at the point of care.

• Total TBSA burned (numeric): The physician must state the percentage explicitly – “75% TBSA” not “extensive burns”
• Third-degree percentage (numeric, as a share of total body surface): Must appear separately from the total TBSA figure – “75% TBSA burned, 72% TBSA third-degree”
• Body region breakdown by depth: A region-by-region depth assessment supports the calculated percentages and defends against audit
• TBSA diagram: Lund-Browder or Rule of Nines diagram, completed and signed, in the medical record
• Physician attestation: The treating burn surgeon or attending must co-sign or attest to the documented percentages if completed by a resident or advanced practice provider
• Consistency across all documentation: Progress notes, operative reports and discharge summaries must state the same TBSA and depth percentages, because conflicting figures trigger denials

Clinical Documentation Improvement (CDI) specialists should query the physician whenever a TBSA diagram is present but the note gives no numeric percentages. The diagram alone is not enough. The percentages must be stated in the note or the query response.

Common claim denial reasons for T31.77 and how to avoid them

T31.77 is a high-value code that draws close payer review. Burn center revenue cycle teams need a denial management in healthcare process that catches these triggers before submission.

Payer requirements and billing context for T31.77

Burns covering 70-79% TBSA are almost universally inpatient admissions, typically to a verified burn center. Emergency admissions do not require prior authorization from Medicare, but transfer authorizations may apply when the patient is being moved between facilities. Document the clinical justification for transfer in the medical record, including the referring facility’s assessment and the burn center’s acceptance criteria.

Commercial payers vary in their authorization requirements for extended burn center stays and reconstructive procedures. When initial authorization is obtained for the admission, confirm whether staged reconstructive procedures scheduled during the same inpatient stay require separate authorization. Some payers treat skin grafting as a separate authorized service even within an authorized admission.

Two claim types come out of one admission. The burn center bills the stay on the UB-04 (837I), which groups to an MS-DRG. Physicians bill their excision, grafting and follow-up work on the CMS-1500 (837P). Knowing how medical billing workflows split that work helps when a case involves multiple payers, coordination of benefits or workers’ compensation.

Coding sequelae and late effects of T31.77-level burns

When a patient returns to treat a condition caused by a healed burn, the sequela is coded on the site-specific burn code, not on T31.77. The seventh character S goes on the T20-T25 code for the region that scarred, such as T21.31XS for the chest wall.

Common late effects at this scale include hypertrophic scarring and keloid (L91.0) and scar conditions or fibrosis of skin (L90.5). Joint contractures take an M24.5- code for the affected joint. Reconstructive procedures such as scar revision or contracture release are reported against these sequela codes.

Sequela coding follows a two-code order. List the sequela condition first, because it is what the provider is treating. Then list the T20-T25 burn code with the S character to show the cause. Reversing this order is a claim error.

How Pabau supports professional claims for T31.77 burn care

A physician claim for T31.77 burn care carries a long code set. It holds the T20-T25 site codes with their seventh characters, plus T31.77 itself. It may add external cause codes and a procedure code for each graft site. One wrong character can stall payment for the whole claim.

Pabau, the practice management and billing platform we build, handles that professional side. Its claims software for practices files electronic CMS-1500 claims through the Claim.MD clearinghouse. Eligibility checks and claim validation run before submission, and ERA remittance data comes back so denials can be tracked by code.

Pabau does not bill the facility side. The burn center’s inpatient claim on the UB-04 (837I), and the MS-DRG it groups to, stay with the hospital’s own billing system.

Get physician burn claims right first time

Pabau files professional claims through Claim.MD, with eligibility checks, pre-submission validation and ERA processing for multi-code burn care claims.

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Conclusion

Code T31.77 from two numbers only: total TBSA burned and the percentage of body surface that is third-degree. If either is missing or the notes disagree, query the physician before you code. A guessed band lands the claim on the wrong T31.7 code, and the payer will notice before you do.

The other errors are mechanical, and a pre-submission check catches them. Keep the seventh character on the site codes and off T31.77, and add external cause codes wherever the payer asks for them. Do that, and a claim this severe gets paid at the level its documentation supports.

Pabau handles that check for the professional claim. Book a demo to see how it validates physician burn-care claims before they reach the payer.

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