2026 ICD-10-CM Diagnosis Code T78.41XSArthus phenomenon, sequela
T78.41XS is a billable ICD-10-CM diagnosis code for arthus phenomenon, 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 922 through 923. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury, sequela.
Code Identity
Code Classification
Present on Admission (POA)Billing
T78.41XS is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Adverse effects, not elsewhere classified (T78). 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.
Convert T78.41XS to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T78.41XSOverview
Is T78.41XS (Arthus phenomenon) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report arthus phenomenon, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character S in T78.41XS mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the arthus phenomenon itself has resolved, not the original event.
What MS-DRG does T78.41XS group to?
When arthus phenomenon, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 922, 923, with relative weights from 1.0177 to 1.7494 depending on complications. Higher weights mean higher Medicare reimbursement.
Is T78.41XS 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 arthus phenomenon, sequela on inpatient claims.
What is the ICD-9 equivalent of T78.41XS?
Under the General Equivalence Mappings, arthus phenomenon, sequela converts to ICD-9-CM 909.9 (late eff exter cause NEC). 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.
