2026 ICD-10-CM Diagnosis Code T78.49XSOther allergy, sequela
T78.49XS is a billable ICD-10-CM diagnosis code for other allergy, 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
T78.49XS 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.
- Allergic gingival disease
- Allergic gingivitis
- Allergic reaction to chemical
- Allergic reaction to cosmetics
- Allergic reaction to flour dust
- Allergic reaction to insect bite
- Allergic reaction to insect venom
- Allergic reaction to plant, except food
- Allergic reaction to radiocontrast media
- Allergic reaction to tattoo ink
- Allergic sensitization
- Allergic sensitization by patch test
- Allosensitization
- Arthropathy associated with a hypersensitivity reaction
- Atopic IgE-mediated allergic disorder
- Cell-mediated cytotoxic disorder
- Cell-mediated cytotoxic reaction
- Cell-mediated immune reaction
- Contact hypersensitivity
- Contrast media adverse reaction
- Delayed hypersensitivity disorder
- Environmental allergy
- Erythrocyte alloimmunization
- Hypersensitivity disorder mediated by immune complex
- Hypersensitivity gingivitis
- IgE-mediated allergic disorder
- Immune hypersensitivity disorder by mechanism
- Jarisch Herxheimer reaction
- Jones-Mote type hypersensitivity
- Nonatopic IgE-mediated allergic disorder
- Non-IgE-mediated allergic disorder
- Non-IgE-mediated atopic disorder
- Phacoanaphylaxis
- Platelet alloimmunization
- Platinum sensitivity
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.
Clinical InformationClinical
Contact Hypersensitivity
contact hypersensitivity is an inflammatory response induced by antigen-reactive t cells that are exposed to antigen on the skin surface (epidermis). poison ivy is a frequent cause of such reactivity, due to the urushiol from the plant, as are a variety of antigens derived from industrial exposure (e.g. rubber, chromate, nickel). these antigens induce the appearance of th1-like t cells, which presumably produce ifn to activate macrophages.
Patient EducationClinical
Allergy
An allergy is a reaction by your immune system to something that does not bother most other people. People who have allergies often are sensitive to more than one thing. Substances that often cause reactions are:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T78.49XS to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T78.49XSOverview
Is T78.49XS (Other allergy) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report other allergy, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character S in T78.49XS mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the other allergy itself has resolved, not the original event.
What MS-DRG does T78.49XS group to?
When other allergy, 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 T78.49XS 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 other allergy, sequela on inpatient claims.
What is the ICD-9 equivalent of T78.49XS?
Under the General Equivalence Mappings, other allergy, 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.
