ICD code T31.98 – Burns involving 90% or more of body surface with 80-89% third degree

Key takeaways

ICD-10 Code T31.98 covers burns across 90% or more of total body surface area (TBSA), with 80-89% of that area third degree. It is billable and valid for FY2025 and FY2026.

T31.98 usually sits alongside T20-T25 site-specific codes as a supplementary extent code. It becomes the principal diagnosis only when the burn site is unspecified.

The physician has to record two separate percentages, total TBSA burned and the share of it that is third degree. Adults are assessed with the Rule of Nines, children with the Lund-Browder chart.

Practice management software like Pabau submits and tracks the multi-code claims these admissions produce, so the coded record reaches the payer intact.

ICD-10 Code T31.98: full description and code details

ICD-10 Code T31.98 is a billable, specific ICD-10-CM code valid for diagnosis reporting and reimbursement. It holds for FY2025 and FY2026, according to the CDC/NCHS ICD-10-CM web tool. It has not been deleted, revised, or replaced in either fiscal year’s update cycle.

The code descriptor uses the term “third degree” in keeping with ICD-10-CM terminology. Clinically, this corresponds to full-thickness burns that destroy both the epidermis and dermis. The two terms are interchangeable in documentation for coding purposes, but ICD-10-CM uses “third degree” in all official code descriptors.

Code hierarchy: where T31.98 fits in ICD-10-CM

T31.98 sits four levels deep in the ICD-10-CM injury chapter. Understanding the parent-child structure is essential for coding the correct level of specificity and for navigating crosswalk tools.

T31 covers burns only. T32 covers corrosions classified by the same extent methodology. A chemical burn from an acid or alkali that destroys tissue is coded to T32, not T31. Assign ICD-10 Code T31.98 only when the burn is thermal, electrical, radiation, or another non-corrosive cause.

T31.98 sibling codes: the T31.90 through T31.99 series

Within subcategory T31.9 (burns involving 90% or more of body surface), the second decimal digit captures the percentage of those burns that are third degree. T31.90 covers less than 10% third-degree involvement, and T31.99 covers 90% or more. T31.98 sits one step below the top of the series.

Because the bands run in 10-point steps, a documented percentage lands in exactly one code. A chart recording 75% third-degree burns out of 92% total TBSA maps to T31.97, the band directly below this one. Read the documented third-degree percentage against the band rather than rounding to the nearest code.

The Rule of Nines and TBSA in burn coding

The American Burn Association describes the Rule of Nines as the standard tool for estimating total body surface area in adults. It divides the adult body into regions each representing approximately 9% of TBSA:

• Head and neck: 9%
• Each upper extremity: 9% (18% total)
• Anterior trunk: 18%
• Posterior trunk: 18%
• Each lower extremity: 18% (36% total)
• Perineum/genitalia: 1%

For a patient to meet the 90%+ TBSA threshold required for any T31.9x code, almost the whole body surface must be involved. Burn center admissions at this level carry very high morbidity and mortality.

The physician’s documentation must capture two distinct percentages. Total TBSA burned establishes the T31.9x subcategory. The share of that total which is third degree selects the sibling code, from T31.90 through T31.99. Without both figures in the record, ICD-10 Code T31.98 cannot be validly assigned.

Pediatric TBSA: the Lund-Browder chart

The standard Rule of Nines does not apply to pediatric patients. Children have proportionally larger heads and smaller lower extremities than adults. The adult formula therefore underestimates head burns and overestimates lower extremity burns. The Lund-Browder chart accounts for age-specific body surface proportions and is the preferred tool for children.

ICD-10 Code T31.98 applies to pediatric patients, with no separate pediatric version. The documentation expectation is what changes. The record should reference the Lund-Browder calculation, and the resulting percentages drive code selection exactly as they do for adults.

Sequencing T31.98 with the T20-T25 site codes

Category T31 is an extent-based classification system. ICD-10-CM Official Guidelines Section I.C.19.d governs how it interacts with the site-specific burn categories (T20-T25). Four rules cover almost every burn admission:

• Burn site specified: assign the T20-T25 site-specific code as the primary code. Add ICD-10 Code T31.98 after it to capture the total extent of involvement.
• Burn site unspecified: assign ICD-10 Code T31.98 as the principal diagnosis when no site documentation is available or the site cannot be determined.
• Multiple burn sites: code each site separately from T20-T25, sequence the highest-degree burn first, and add T31.98 as a supplementary extent code.
• Inpatient admissions: T31 codes are particularly valuable in inpatient settings where total extent drives DRG grouping and resource allocation documentation.

The order that appears on the claim then depends on whether the record names a burn site.

The most common sequencing error with ICD-10 Code T31.98 is assigning it as the sole diagnosis when site-specific codes exist in the record. Payers reviewing severe burn claims expect to see T20-T25 site codes as the primary diagnosis codes when sites are documented. Claims submitted with only a T31.98 and no site codes may trigger medical necessity reviews, particularly for burn center level-of-care billing.

Complication and external cause codes

Severe burns at the T31.98 severity level rarely present without complications. The CMS ICD-10-CM coding guidance and Official Guidelines require coders to report all conditions that affect patient management during the encounter. For a burn patient with 90%+ TBSA involvement, this typically means a complex multi-code claim.

Sequencing also matters downstream. A burn admission this large reaches the payer through a clearinghouse, which checks the submission against payer edits first. Codes that arrive out of order are caught there, before the carrier ever sees the claim.

Common additional codes reported alongside T31.98

When T59.x inhalation injury codes co-occur with ICD-10 Code T31.98, sequencing follows the reason for the encounter. If the patient is admitted primarily for the burns, the T20-T25 site codes and T31.98 come first. Inhalation and complication codes follow them. Check each added code against the ICD-10-CM codes reference before submission, because a wrong descriptor at this acuity invites a payer review.

Documentation requirements for accurate T31.98 assignment

Inadequate burn documentation is one of the most common reasons T31.98-level claims face payer scrutiny. Clinical documentation improvement (CDI) teams working with burn center physicians should verify the following elements are captured before the claim is coded.

• Total TBSA percentage: the physician must document the estimated percentage of body surface affected. The Rule of Nines calculation or the Lund-Browder chart notation should be referenced.
• Third-degree burn percentage: this must be documented separately from total TBSA. A note stating “90% body surface burns” without a third-degree breakdown leaves the coder unable to select between T31.90 and T31.99.
• Burn site(s): each anatomic region involved must be documented to allow site-specific T20-T25 code assignment.
• Burn depth by site: superficial, partial-thickness, and full-thickness depths should be recorded for each involved region when clinically assessable.
• Burn cause: thermal (flame, scald, contact), electrical, radiation, or chemical. The cause determines whether T31 or T32 applies, and which external cause code is correct.
• Complications present: inhalation injury, sepsis, acute kidney injury, or respiratory failure each require explicit physician documentation for additional code assignment.

Burn cases at this severity carry high DRG weights, so payers audit them more closely than routine admissions. A clean claim for a T31.98 case needs every element above documented. It also needs those elements to agree across the physician notes, the nursing assessment, and the discharge summary.

ICD-9-CM crosswalk for T31.98

Legacy system users and researchers working with pre-October 2015 claims data will encounter ICD-9-CM codes rather than ICD-10-CM. The approximate ICD-9-CM equivalent for T31.98 is 948.98, which represents the same clinical concept under the older classification system.

This crosswalk is derived from the CMS General Equivalence Mappings (GEMs). The mapping is approximate rather than exact, because ICD-9-CM and ICD-10-CM use different classification logic. It works for research and for historical data analysis. For current billing, only ICD-10-CM codes apply. Code status can be verified through the AAPC ICD-10-CM code search.

Special populations: pediatric and geriatric considerations

ICD-10 Code T31.98 applies uniformly across age groups, with no separate pediatric or geriatric variant. Documentation expectations, however, differ meaningfully by age.

Pediatric patients

Pediatric burns require the Lund-Browder chart for TBSA estimation, as noted above. Coders should confirm that the chart, or an age-adjusted equivalent, was used instead of the adult Rule of Nines. A record showing only an unadjusted Rule of Nines figure may overstate or understate TBSA. The CDI team should raise that as a query before the case is coded.

Non-accidental injury burns must also be considered. When abuse is suspected or confirmed, report additional codes from the T74.x series alongside the burn codes. That series covers adult and child abuse, neglect, and other maltreatment. The burn coding itself stays the same, and the maltreatment codes are added to it.

Geriatric patients

Older adults with burns covering 90%+ TBSA face a substantially higher mortality risk, because physiological reserve is lower. Coding this population usually means additional comorbidity codes such as hypertension, diabetes, and chronic kidney disease. Those codes reflect the complexity of care and support medical necessity for prolonged intensive care. The billing team should confirm they are all represented before submission, since they affect DRG assignment at these severity levels.

How Pabau supports T31.98 claim submission

At this severity level, claims come from burn center inpatient admissions billed on UB-04 or CMS-1500 forms. One admission can carry several T20-T25 site codes, the T31.98 extent code, external cause codes, and a run of complication codes. Assembling that list by hand, from notes held in separate systems, is where detail goes missing.

Practice management software like Pabau keeps the patient record, the treatment notes, and the invoice in one system. The codes recorded during the encounter travel with the charge, so the billing team is not rekeying them from a second document. Fewer transcription steps mean fewer of the code-combination errors that hold a burn claim up.

Pabau’s claims management software then tracks each submitted claim and the reason attached to any denial. Reviewing those reasons across similar admissions shows which code combinations keep coming back. That is faster than reopening cases one at a time to find the pattern.

Keep complex burn claims moving

Pabau keeps the patient record, the treatment note and the invoice in one system, then tracks each submitted claim and the reason behind any denial. Your billing team stops rekeying codes between documents.

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Conclusion

T31.98 is decided by the record, not by the coder. Where the physician documents both percentages and every burn site, the code and its sequence follow without a query. Where either number is missing, the claim stops until someone asks for it.

The practical move is to build the two-percentage check into the burn admission itself, rather than catching it at coding. That puts the question in front of the surgeon while the wound assessment is still open, and keeps a high-weight DRG claim moving. The cost is a small amount of front-loaded effort against a retrospective query that can hold payment for weeks.

Book a demo to see how Pabau carries a coded burn admission from the patient record through to the payer’s response.

Continue your research

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