ICD code T24.221A – Second-degree burn of right knee

Key takeaways

T24.221A is valid and billable in FY 2026 and FY 2027 ICD-10-CM. It covers a second-degree burn of the right knee during active treatment.

7th character A applies to every visit while active treatment continues, including later visits. Switching to D too early is a frequent audit finding.

The tabular note instructs an additional external cause code for the burn source and place of occurrence. Reporting is required only where a payer or state mandates it.

External cause codes always sequence after T24.221A and are never the principal diagnosis.

Laterality mismatch, such as coding the left knee when the provider documented the right, is a common denial reason. Check it before submission.

ICD-10 Code T24.221A: Code definition and clinical scope

ICD-10 Code T24.221A is the billable ICD-10-CM code for a second-degree thermal burn of the right knee while the patient receives active treatment.

The 7th character A marks that initial encounter and completes the code. According to the CDC/NCHS ICD-10-CM web tool, T24.221A is valid for claims with service dates in FY 2026 and FY 2027.

The code sits in chapter S00-T88, which covers injury, poisoning and certain other consequences of external causes. Its category is T24, burn and corrosion of lower limb, except ankle and foot. The hierarchy runs T24 > T24.2 (second-degree burns, lower limb) > T24.22 (burn of second degree of knee) > T24.221 (right knee, requires 7th character) > T24.221A. Neighboring burn and injury codes from the same chapter sit in our library of diagnostic codes for coders.

Burns of the ankle and foot (T25.-) and hip region (T21.-) are Excludes2 at T24. Corrosion of the right knee has its own code, T24.621A.

Burn depth classification: Where second degree fits

Burn depth determines both clinical management and which ICD-10 code to assign. The table below maps each degree to its right-knee ICD-10-CM code and clinical indicators.

Provider documentation must use the term “second degree” or “partial thickness” explicitly. A note that only says “burn to right knee” does not support a second-degree code. Payers cite that missing depth as a documentation deficiency on audit.

Understanding the 7th character: A, D, and S for T24.221

The three valid 7th characters for T24.221 are A (initial encounter), D (subsequent encounter), and S (sequela). Selecting the wrong one is an OIG audit target and a common payer denial trigger.

How to select the correct 7th character

Per ICD-10-CM Official Guidelines Section I.C.19.a, “active treatment” is the key test, not visit number. Apply this decision sequence before assigning the 7th character:

1. Is the provider actively treating the burn wound today? (wound care, debridement, skin graft) If yes: use A.
2. Is the wound healing with routine follow-up only? (monitoring, dressing change only, wound check) If yes: use D.
3. Has the burn fully healed, and is the patient presenting for a complication caused by that healed burn? (scar contracture, keloid, sensory change) If yes: use S, and code the complication first.

A patient who returns for wound debridement on visit six still gets T24.221A, not T24.221D. The AHA Coding Clinic reinforces that “initial encounter” in ICD-10-CM refers to active-treatment encounters throughout the episode of care, not only the first calendar visit.

Neighboring codes and laterality: Avoiding common mix-ups

Laterality errors are among the most common reasons T24.221A claims are denied. Payers can compare the provider’s note against the submitted code, and a left/right mismatch triggers an automatic edit rejection. The table below covers the five codes most often confused with T24.221A.

Coding T24.229A (unspecified knee) when the provider documented “right” can also raise a medical necessity question. Some payers deny it because a less specific code may not support the treatment intensity billed.

Required companion codes for T24.221A

The tabular note under T24 instructs an additional external cause code to identify the burn source and place (X00-X19, X75-X77, X96-X98, Y92). Guideline I.C.20.a sets no national mandate, so reporting is required only where a payer or state mandates it. External cause codes are never the principal diagnosis, and T24.221A always sequences first.

Three companion code categories are commonly reported with it.

Common external cause codes used with T24.221A

X-category external cause codes carry the same 7th character as T24.221A. Y92 and Y93 codes have none, as the claim line below shows.

Pairing T24.221A (initial encounter) with an X code carrying 7th character D creates a conflict that payer edits will flag. Match the 7th character on every code that carries one.

Documentation requirements for a second-degree right knee burn

Provider documentation must support T24.221A on six points before the claim can go out clean. Missing any one of them exposes the claim to a medical necessity denial or downcoding for lack of specificity.

• Explicit laterality: The note must say “right knee” or “right lower limb, knee region.” A note that says “burn to knee” without a side forces the coder to T24.229A (unspecified). Payers often reimburse that code at a lower rate or deny it outright.
• Explicit burn depth: “Second degree” or “partial thickness” must appear in the assessment. “Blistering burn” alone is insufficient without a depth qualifier. The coder cannot infer degree from clinical signs.
• Anatomical precision: The knee includes the anterior surface, popliteal fossa, and medial/lateral aspects. Document which surface was burned to satisfy medical review criteria.
• Encounter type justification: The note must show active treatment, such as a wound care procedure, debridement or a graft, before 7th character A applies. A visit note that reads only “wound healing well, return in two weeks” supports D, not A.
• Cause of burn: Document the external heat source (hot water, flame, hot object) to allow the coder to assign the correct X-category external cause code.
• Total body surface area (TBSA): Many payers require TBSA documentation for wound care reimbursement. The Rule of Nines gives 18% per leg (9% anterior, 9% posterior). Estimate TBSA for the burned area and document it to meet LCD requirements.

Each item on the checklist maps to a field payers audit under medical necessity review. Together they are what turns a burn encounter into a clean claim.

CPT codes commonly billed with T24.221A

T24.221A is a diagnosis code, not a procedure code. It pairs with a CPT code that reflects the work done at the encounter. The table below covers the most frequently billed pairings, drawing on standard medical billing workflow guidance for wound care encounters.

NCCI bundling edits apply to CPT 16020 and 97597 when billed on the same date of service. Append modifier 59 or XS only when a distinctly separate wound site or service session is documented. A superbill that captures wound size, anatomical location, and debridement method at the point of care prevents the most common pairing denials.

Why T24.221A claims get denied and how to fix them

Denied T24.221A claims fall into a predictable set of error patterns, which makes structured denial management pay off quickly. The table below maps each denial reason to its root cause and the fix.

Many of these denials can be fixed with a corrected claim rather than a formal appeal, as long as the note already supports the change.

How Pabau keeps T24.221A claims accurate from note to payment

In many wound care practices, a coder copies the diagnosis, external cause codes and CPT pairing from the note into a separate billing tool. Each re-key is another chance to swap right for left or drop the X code.

Pabau, the practice management platform we build, keeps the treatment note, the invoice and the claim in one patient record. Its claims software for practices runs validation checks each time a claim is sent, confirming details like membership numbers and authorization codes. US claims go to payers electronically through the Claim.MD integration.

Eligibility checks, claim status and ERA remittance posting sit on the same dashboard. Catching errors at the practice level reduces the number of claims that reach the appeals cycle, and your billing team spends less time reworking denials.

Submit burn claims without the back-and-forth

Pabau keeps the burn note, the invoice and the claim in one record. Your coder sends T24.221A with the codes the note supports, from the same dashboard.

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Conclusion

T24.221A is rarely hard to code. The provider note is where these claims are won or lost. A coder can only assign A, the right side and second degree when the note states all three.

So build laterality, depth, active treatment and the heat source into your burn note template. The trade-off is a slightly longer note at each wound care visit, which costs far less than a corrected claim and a delayed payment.

Book a demo to see how Pabau keeps burn and wound care claims accurate from the first note to the final payment.

Continue your research

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Want to understand how clearinghouse validation catches code errors before the payer sees them? Claim.MD clearinghouse overview explains how electronic claim scrubbing flags diagnosis-code issues such as a missing 7th character or companion code.

Looking for guidance on revenue cycle management for wound care practices? Revenue cycle management in healthcare walks through the end-to-end billing workflow from code assignment through payment posting.

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