ICD code T31.55 – Burns involving 50-59% of body surface

Key takeaways

T31.55 applies only when the physician documents total burns of 50-59% TBSA and third-degree burns that also cover 50-59% of the body.

Coders cannot estimate TBSA, so the figure must come from the physician’s Rule of Nines, Lund and Browder, or palmar assessment.

T31.55 is usually an additional code, reported after the site-specific T20-T25 burn codes that say where the burns are.

Third-degree burns under 10%, or depth left unspecified, point to T31.50, so query the physician before settling on it.

In the burn MS-DRGs, ventilation over 96 hours, skin grafting, inhalation injury and CC/MCC status decide which DRG the admission groups to.

ICD-10 code T31.55: Official description and classification

ICD-10 Code T31.55 is a valid, billable ICD-10-CM diagnosis code for burns involving 50-59% of body surface with 50-59% third degree burns. That is its official descriptor in the CDC/NCHS ICD-10-CM browser. The code belongs to category T31, which classifies burns by extent and sits apart from the site-specific burn codes T20 through T25.

The T31 category adds extent data to the anatomical burn codes. Under the CMS ICD-10-CM Official Guidelines for Coding and Reporting, Section I.C.19.d, a T31 code reports burn extent when T20-T25 codes already capture the site.

The guidelines also call for a T31 code when third-degree burns cover 20% or more of the body surface. Every T31.55 case clears that threshold.

What T31.55 covers: Clinical criteria and definitions

T31.55 requires two clinical thresholds at once. Total burns must cover 50-59% of total body surface area (TBSA), and full-thickness (third-degree) burns must also cover 50-59% of the body. The physician has to document both figures explicitly, and the four checks below take a chart from burn assessment to a supported code.

Clinicians use three accepted assessment tools to calculate the TBSA percentage behind the first check:

• Rule of Nines (Wallace method): Divides the body into regions of 9% each. These are the head, each arm, the upper and lower halves of the front and back of the trunk, each thigh, and each lower leg. The perineum accounts for the remaining 1%. It gives a rapid bedside estimate and is the standard method for adults.
• Lund and Browder chart: An age-adjusted diagram that redistributes body surface proportions. More accurate than Rule of Nines for pediatric patients and for large, irregular burns across multiple regions.
• Palmar method: The patient’s palm (including fingers) represents approximately 1% TBSA. Used for scattered or patchy burns when systematic charting is impractical.

Third-degree burns destroy the full dermis, including hair follicles, sweat glands, and nerve endings. Clinically, the wound is dry, leathery and insensate, and it may look white, brown, or black. The physician makes the depth determination. Code assignment rests on provider documentation, so a coder cannot assign burn depth from descriptions in nursing notes alone.

T31.5x subcode breakdown: Choosing the right fifth character

The T31.5x group covers all burns with a total extent of 50-59% TBSA. The fifth character specifies how much of that total extent is third-degree. T31.55 sits at the most severe end of the subgroup.

A frequent fifth-character error is defaulting to T31.50 when depth is undocumented. That code covers 0-9% third degree, and the tabular list also files 50-59% burns with no further detail under it. Query the physician for a depth determination first. A record with skin grafts or a burn ICU stay usually points to more full-thickness involvement than T31.50 reports.

Excluded conditions: What T31.55 does not cover

T31.55 does not cover corrosions, sunburn, or erythema ab igne. Each has its own classification, so none of them is coded to T31.

• Corrosions (T32): Chemical burns caused by acids, alkalis, or other corrosive substances are classified under T32, not T31. T32 follows the same extent-and-depth structure, so T32.55 covers corrosions of 50-59% TBSA with 50-59% third degree. The documented mechanism, thermal or chemical, determines whether T31 or T32 applies.
• Sunburn (L55.-): Sunburn is excluded from the burn codes. Coding it to T31 misrepresents both the mechanism and the severity.
• Erythema ab igne (L59.0): These chronic skin changes come from repeated heat exposure and are not a burn in the ICD-10-CM sense.
• Site-specific burn codes T20-T25: T31.55 does not replace these codes. When the burn site is documented, both the anatomical code and T31.55 are required.

Correct code sequencing for T31.55

T31.55 is almost always sequenced as an additional code, after a site-specific principal diagnosis. Inpatient burn admissions follow the UHDDS sequencing rules together with the burn guidelines.

Per CMS ICD-10-CM Official Guidelines Section I.C.19.d, the standard sequencing pattern for an inpatient burn admission is:

1. Principal diagnosis: The site-specific burn code from T20-T25 that best describes the burn location and degree (e.g. T25.321A, third-degree burn of right foot, initial encounter). When burns of several depths are present, the highest-degree burn goes first.
2. Additional code: T31.55 to document total body surface extent and third-degree proportion.
3. Additional codes as needed: External cause codes for mechanism and place, plus codes for associated conditions such as respiratory tract burns (T27.-) or sepsis (A41.-).

T31.55 goes first only when the burn site is unspecified, which is uncommon on a burn admission.

Inpatient and outpatient rules also differ. Under UHDDS rules, the inpatient principal diagnosis is the condition established after study. Outpatient encounters are coded to the highest degree of certainty. T31.55 on an outpatient record without a site-specific code needs strong clinical justification and tends to draw audit attention.

Documentation requirements to support T31.55

A clean claim submission for T31.55 depends on physician documentation that explicitly captures each element below. Missing any one of them gives the payer grounds for a medical necessity denial.

MS-DRG assignment and reimbursement impact

Burn admissions group to the burn MS-DRGs in MDC 22, and T31.55 documents the extent that marks the case as an extensive burn. Within that family, mechanical ventilation over 96 hours, skin grafting, inhalation injury and CC/MCC status decide the DRG.

MS-DRG relative weights change annually. Facilities should verify current weights from the CMS ICD-10 updates page before budgeting reimbursement for T31.55 encounters. Sound revenue cycle management pairs accurate T31.55 assignment with timely graft procedure coding. A missed graft code moves the admission to a lower-weighted DRG such as 933 or 934.

Common coding errors and claim denial reasons

T31.55 claims are denied for a predictable set of reasons. Understanding each one reduces avoidable rework and supports denial management workflows for burn center billing teams.

• Missing TBSA percentage in the chart: This is a frequent denial trigger. If the physician documents “extensive burns” without a numeric TBSA figure, the coder cannot assign T31.55. Query required.
• T31.55 submitted without a companion T20-T25 code: Payers expect a site-specific code alongside T31.55. Submitting T31.55 as the only burn code, with no anatomical detail, tends to fail medical necessity edits.
• Confusing T31 with T32 (burn vs corrosion): A chemical burn from an industrial solvent is a corrosion (T32.55), not a thermal burn (T31.55). The documented mechanism, thermal or chemical, determines whether T31 or T32 applies.
• Incorrect fifth character: Assigning T31.55 when the documented third-degree share is 40-49% (T31.54) is overcoding, and it may attract recovery audit scrutiny.
• Outpatient use without justification: T31.55 on an outpatient claim without clearly documented 50-59% TBSA will trigger a medical necessity denial. Burns at this extent require hospitalization, so outpatient assignment signals a mismatch between documentation and claim.
• Missing depth documentation: When depth is described only in nursing notes rather than a physician assessment, some payers reject the third-degree qualifier. The physician or treating clinician must own the depth determination.

Reviewing the common denial codes next to these T31.55 audit patterns helps billing teams build targeted edits before submission.

T31.55 vs related codes: Side-by-side comparison

Four codes are most often confused with T31.55, including T32.55 for corrosions of the same extent. The table below shows the deciding difference for each.

Payer-specific requirements and prior authorization

Burns at the T31.55 severity level are major hospitalizations. Commercial payers and some Medicaid programs often require authorization or concurrent review for these admissions, while Medicare applies medical-necessity review. Documentation thresholds vary by payer. Meeting medical billing compliance standards for burn center encounters means anticipating those requirements before the claim is submitted.

• Medicare: Inpatient burn admissions need no prior authorization, but medical-necessity review applies. No specific LCD governs T31.55 directly. Documentation must support the TBSA classification and inpatient level of care.
• Medicaid: State-specific. Some states require prior authorization for burn center transfers. TBSA documentation and burn center designation strengthen the record, and ABA-verified centers carry more weight in medical necessity appeals.
• Commercial payers: Many use InterQual or MCG criteria for burn hospitalization review. A documented T31.55 case typically meets criteria. Missing TBSA documentation is a common reason for concurrent review denials.
• Responding to additional documentation requests (ADRs): Attach the burn diagram, the physician burn assessment note, and any burn center designation documentation. These three components address the most frequent payer queries.

Claims management software with payer-specific edits flags a missing TBSA figure or site code before submission. That cuts the number of ADRs a burn billing team has to answer.

How Pabau supports professional claims for burn care

Burn surgeons and the practices that follow up burn patients bill professional claims, and T31.55 rides on those claims next to the site codes. Without a connected billing system, staff often key them into a payer portal by hand, where a missing site code is easy to overlook.

Pabau, the practice management platform we build, creates CMS-1500 claims from the visit invoice and sends them through its Claim.MD clearinghouse integration. Real-time eligibility checks run from the patient record, so coverage is confirmed before the follow-up visit.

Claim status updates and electronic remittance advice flow back into Pabau, matched to the claims they settle. Your team sees a rejected burn claim as soon as it returns and can correct the code while the filing window is still open.

Send cleaner burn care claims with Pabau

Pabau creates CMS-1500 claims from each visit, checks eligibility in real time, and sends claims through Claim.MD to thousands of US payers. Remittance advice comes back matched to each claim.

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Conclusion

T31.55 rests on two physician-stated numbers, and the code should not go on a claim until both are in the chart. When either figure is missing, query the physician before you code. A query delays the claim, but a wrong fifth character can move the whole admission to a different DRG.

Sequence the T20-T25 site codes first, add T31.55 for extent, and confirm the mechanism is thermal before the claim leaves. Those three habits head off the denial reasons covered above. Book a demo to see how Pabau turns each burn care visit into a clean professional claim, with eligibility checked up front.

Continue your research

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Want to see how a clearinghouse handles your claims? Claim.MD clearinghouse overview details how electronic claims reach Medicare and commercial payers with real-time status tracking.

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