ICD code T31.86 – Major burns covering 80-89% of body surface

Key takeaways

T31.86 covers burns on 80-89% of body surface with third-degree burns on 60-69%, and the physician record must state both percentages.

When the burn sites are documented, T31.86 is a supplementary code that follows the T20-T25 site codes, which carry the seventh character.

T31.86 groups to MDC 22, where a skin graft, ventilation over 96 hours and inhalation injury decide the DRG.

T31.86 may carry CC/MCC status, so verify it against the current CMS CC/MCC list before you rely on it.

T31.86 takes no seventh character, because the A, D or S belongs to the companion site code.

Claims management software such as Pabau helps billing teams review T31.86 claims before submission.

ICD-10 code T31.86: Definition and classification logic

ICD-10 code T31.86 is the billable code for burns covering 80 to 89% of total body surface area (TBSA).

Third-degree burns cover 60 to 69% of the body surface. It belongs to category T31, “Burns classified according to extent of body surface involved.”

Category T31 records how much of the body is burned and how much of it is full-thickness. It says nothing about where the burns are or what caused them.

The code is valid and billable for fiscal years 2025 and 2026 in the ICD-10-CM code set, per the CMS Tabular List. It is a leaf-node code with no further subdivision, so T31.86 is used exactly as written.

How the two percentages combine

T31.86 rests on two independent numbers, and a claim fails if the documentation doesn’t support either one. The first is total TBSA, meaning 80 to 89% of the body surface is burned at any depth. The second is the third-degree share, meaning full-thickness burns cover 60 to 69% of the body surface.

Third-degree burns destroy the epidermis and dermis and extend into subcutaneous tissue. They are insensate, look white, tan, brown or charred, and usually need grafting.

A patient with 85% total burns and 65% full-thickness burns meets the T31.86 criteria exactly. The scale below shows how the code moves when only the third-degree figure changes.

If the third-degree figure falls to 55%, the code drops to T31.85. If it rises to 72%, the correct code is T31.87.

How to calculate TBSA and apply the rule of nines

The rule of nines divides the adult body into segments each representing 9% of total surface area. Clinicians sum the affected segments to arrive at TBSA. The standard adult segmentation is as follows:

For pediatric patients, the rule of nines underestimates head size and overestimates leg size. The Lund-Browder chart adjusts for age-related surface area proportions and is the preferred tool for patients under 15. For ICD-10 coding purposes, the TBSA and degree percentages must come from the physician’s documented assessment, not from the coder’s independent calculation.

Where T31.86 sits in the T31 subcategory

The T31.8 subcategory covers the 80 to 89% total TBSA band. The final digit gives the percentage of body surface with third-degree burns. The table lists every code in the subcategory, so coders can confirm the assignment at the boundaries.

Required additional codes when reporting T31.86

Per ICD-10-CM Official Guidelines Section I.C.19.d, T31.86 is rarely reported alone. Category T31 records the extent of the burn. When the burn sites are documented, it accompanies a T20-T25 site code for each site, which records the anatomic location and depth.

• Site-specific burn code (T20-T25): Required. Identifies the body region burned, depth, and encounter type via the seventh character.
• Seventh character on T20-T25: A = initial encounter, D = subsequent encounter, S = sequela. T31.86 itself takes no seventh character.
• Multiple site codes: When burns span several anatomic regions, report each affected site separately. All companion codes apply to the same T31.86 entry on the claim.
• Inhalation injury (T59.x): Code separately when documented. Inhalation injury is common in large burns and frequently affects DRG assignment.
• Sequencing: Per the T31 category note and Official Guidelines Section I.C.19.d, T31 is the primary code only when the burn site is unspecified. When the site is documented, list the T20-T25 site codes first, starting with the highest degree of burn. T31.86 then follows as a supplementary code.

Site-specific burn codes used with T31.86

The table below shows commonly paired T20-T25 codes for third-degree burns at major anatomic sites, with the initial encounter seventh character applied:

When a patient has burns at multiple sites, each site gets its own T20-T25 code with the appropriate seventh character. T31.86 appears once on the claim, however many site codes are listed.

Documentation requirements to support ICD-10 code T31.86

T31.86 can’t be assigned from a narrative description of a “massive” or “extensive” burn. The physician record must give explicit numbers for both percentages. If either is missing, the coder must query the physician or fall back to a less specific code, which can lower the DRG weight.

These documentation elements must be present, per medical billing compliance principles and ICD-10-CM Official Guidelines Section I.C.19.d:

• Total TBSA percentage: Must fall in the 80-89% range, stated explicitly (e.g., “85% TBSA”).
• Third-degree percentage: Must fall in the 60-69% range, stated explicitly (e.g., “65% full-thickness”). This is the most frequently missing element.
• Body regions affected: Each affected anatomic region documented separately to support the companion T20-T25 codes.
• Burn depth per region: Depth must be documented for each affected site so site-specific codes can be assigned correctly.
• Burn etiology: Flame, scald, chemical or electrical. The cause shapes companion coding and the external cause code.
• Presence or absence of inhalation injury: Documented explicitly, so the coder doesn’t have to infer it from clinical context.

A note reading “patient has large burns covering most of the body surface with deep partial and full-thickness involvement” gives no basis for T31.86. The coder can’t estimate the percentages independently.

MS-DRG assignment and reimbursement impact

T31.86 maps to MDC 22 (Burns) in the CMS MS-DRG grouper. Within MDC 22, three factors decide the DRG: a skin graft, mechanical ventilation (MV) past 96 hours, and inhalation injury. Complications or comorbidities (CC) and major complications or comorbidities (MCC) split DRGs 928 and 929.

T31.86 may carry CC/MCC status. Verify it against the current fiscal year’s CMS CC/MCC list before submission, because the designation can change in annual updates.

Verify current DRG weights against the CMS ICD-10 codes page for the active fiscal year. Report the ICD-10-PCS skin graft procedure codes accurately alongside T31.86. Without them, the grouper can’t assign a graft DRG (927-929) and falls back to a non-graft DRG.

The broader revenue cycle management workflow shows where a T31.86 claim sits in the full payment lifecycle.

Coding T31.86 for subsequent encounters and sequelae

Coders sometimes assume T31.86 carries a seventh character that changes with the encounter type. It doesn’t. T31.86 is reported the same way at initial and subsequent encounters, and the seventh character sits on the companion T20-T25 code.

• Initial encounter (seventh character A on T20-T25): Active treatment period. T31.86 is reported as an additional code alongside the site-specific code(s).
• Subsequent encounter (seventh character D on T20-T25): Routine care during healing. Change the seventh character on the site code from A to D. T31.86 is reported the same way.
• Sequela (seventh character S on T20-T25): Late effects such as burn scars, contractures or functional limitations. The site code takes the S character, plus a code for the late effect (for example, L90.5 for scar conditions). T31.86 is not reported at sequela encounters, because the T31 extent code describes the active burn, not the long-term residual.

On outpatient wound care visits, coders sometimes carry T31.86 forward from the original admission. It belongs on the claim only while the burn extent is still clinically relevant. For sequela-only visits, drop T31.86 and report the site code with the S character plus the sequela diagnosis.

Common coding errors and claim denial reasons

Six errors are worth screening for on every T31.86 claim. Fixing them before submission costs far less than working a denial queue on high-value admissions. Good denial management workflows catch most of them at the pre-submission audit.

• Missing site-specific burn code: T31.86 submitted without a T20-T25 site code when the record documents the burn sites. This breaks the T31 sequencing rule and is likely to fail payer edits.
• TBSA or degree percentage not documented: The most common reason T31.86 cannot be assigned. Coders cannot substitute clinical judgment for explicit physician documentation. If percentages are absent, query the physician before coding.
• Wrong code due to boundary confusion: Using T31.86 when the documented third-degree percentage is 70-79% (correct code: T31.87) or 50-59% (correct code: T31.85). Check the exact numbers in the record.
• Incorrect sequencing: Listing T31.86 first when the burn sites are documented. In that case the T20-T25 site code with the highest degree of burn leads, and T31.86 follows as a supplementary code. Follow Official Guidelines Section I.C.19.d.
• Omitting inhalation injury code: When the record documents smoke inhalation or respiratory burn injury, a T59.x code must appear. Missing it can affect both DRG assignment and payer audits.
• Wrong seventh character on the site code: Using A on a subsequent encounter or D on an initial admission. The seventh character on T20-T25 must match the encounter type.

Submitting a clean claim on a T31.86 admission starts with a pre-submission check:

• Each T20-T25 site code is present, with the correct seventh character.
• T31.86 is present and sequenced after the site codes.
• An inhalation injury code is present, if the record documents one.
• Sequencing has been confirmed against the guidelines.

Teams that pair their billing workflow with electronic remittance advice processing can spot denial patterns sooner and fix the root causes.

T31.86 vs adjacent codes: Choosing the right code

The T31.8 subcategory spans nine codes, T31.80 to T31.88, each covering a 10-percentage-point band of third-degree involvement. The boundary between T31.86 and T31.87 causes the most confusion, because one percentage point in the documented figure changes the code. When the record says 70%, use T31.87. When it says 69%, use T31.86. Never round or approximate.

The CDC/NCHS ICD-10-CM web tool lets coders check the official descriptor for any T31 code and confirm it is valid this fiscal year. The AAPC Codify ICD-10-CM lookup adds code edits, crosswalks and coding notes. CMS publishes the annual tabular updates and coding guidelines on its ICD-10 codes page, linked above.

How claims management software supports T31.86 claim accuracy

Checking an extensive-burn claim by hand means reading the physician note, matching each site code and confirming the sequencing, one line at a time. A missing percentage often surfaces only when the denial arrives, long after the claim joined the medical billing queue.

Pabau, the practice management platform we build, keeps diagnosis codes, clinical notes and payments in the same patient record. Its claims tools help billing teams review claims before submission. The TBSA figures and site codes get checked against the note in one place.

The outcome is fewer resubmissions on high-weight claims. Your billing team spends its time on physician queries instead of rework.

Catch coding errors before the claim goes out

Pabau’s claims management tools help billing teams review claims before submission. Codes, notes and payments sit in one patient record, so T31.86 errors are easier to catch early.

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Conclusion

T31.86 rests on two numbers, and both have to be in the physician’s note. An 80 to 89% TBSA burn with 60 to 69% third-degree involvement usually places the admission in a high-weight DRG family. That makes a missing percentage an expensive omission.

So move the check upstream. Confirm both figures at the assessment, list the T20-T25 site codes first and add T31.86 after them. A one-point slip in the third-degree figure changes the code, so query the physician rather than estimate.

The trade-off is a little more time at intake against a much slower denial later. Book a demo to see how Pabau helps your billing team catch coding errors before a claim goes out.

Continue your research

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