2026 ICD-10-CM Diagnosis Code S90.521SBlister (nonthermal), right ankle, sequela
S90.521S is a billable ICD-10-CM diagnosis code for blister (nonthermal), right ankle, sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 604 through 605. The code is exempt from POA reporting. Coders also document this condition as blister of ankle with infection. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury, sequela.
Code Identity
Code Classification
Present on Admission (POA)Billing
S90.521S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Blister of ankle with infection
- Superficial injury of right ankle
- Traumatic blister of ankle
- Traumatic blister of ankle, infected
- Traumatic blister of right ankle
- Traumatic blister of right ankle with infection
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Superficial injury of ankle, foot and toes (S90). Use the following options for the applicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Blisters
Blisters are fluid-filled sacs on the outer layer of your skin. They form because of rubbing, heat, or diseases of the skin. They are most common on your hands and feet.
The full article covers:
- What are blisters?
- What causes blisters?
- What are the treatments for blisters?
- Can blisters be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert S90.521S to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S90.521SOverview
Is S90.521S (Blister (nonthermal), right ankle) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report blister (nonthermal), right ankle, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character S in S90.521S mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the blister (nonthermal), right ankle itself has resolved, not the original event.
What MS-DRG does S90.521S group to?
When blister (nonthermal), right ankle, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 604, 605, with relative weights from 0.9160 to 1.4721 depending on complications. Higher weights mean higher Medicare reimbursement.
Is S90.521S exempt from POA reporting?
Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for blister (nonthermal), right ankle, sequela on inpatient claims.
What is the ICD-9 equivalent of S90.521S?
Under the General Equivalence Mappings, blister (nonthermal), right ankle, sequela converts to ICD-9-CM 906.2 (late eff superficial inj). The mapping is approximate, so confirm the match fits the documentation.
Footnotes
[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.
