2026 ICD-10-CM Diagnosis Code S90.521DBlister (nonthermal), right ankle, subsequent encounter
S90.521D is a billable ICD-10-CM diagnosis code for blister (nonthermal), right ankle, subsequent encounter. The 7th character D marks it as a subsequent encounter code, used during routine care in the healing or recovery phase. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 949 through 950. 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 Superficial injury; contusion, subsequent encounter.
Code Identity
Code Classification
Present on Admission (POA)Billing
S90.521D 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 S90.521D to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S90.521DOverview
Is S90.521D (Blister (nonthermal), right ankle) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report blister (nonthermal), right ankle, subsequent encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character D in S90.521D mean?
The final character D marks a subsequent encounter: use it for routine care while the blister (nonthermal), right ankle is healing, after active treatment has ended.
What MS-DRG does S90.521D group to?
When blister (nonthermal), right ankle, subsequent encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 949, 950, with relative weights from 0.6277 to 1.1897 depending on complications. Higher weights mean higher Medicare reimbursement.
Is S90.521D 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, subsequent encounter on inpatient claims.
What is the ICD-9 equivalent of S90.521D?
Under the General Equivalence Mappings, blister (nonthermal), right ankle, subsequent encounter converts to ICD-9-CM V58.89 (other specfied aftercare). 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.
