2026 ICD-10-CM Diagnosis Code T78.49XAOther allergy, initial encounter

ICD-10-CM Codes›S00–T88›T66-T78›T78

ICD-10-CM T78.49XA
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T78.49XA is a billable ICD-10-CM diagnosis code for other allergy, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 915 through 916. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Allergic reactions.

Code Identity

ICD-10-CM Code
T78.49XA
Billable Status
Yes — Valid for Submission
Code Describes
Other allergy, initial encounter
Short Description
Other allergy, initial encounter
Same as the full description in the CMS dataset.
Parent Code
T78.49
Other allergy

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT66-T78Other and unspecified effects of external causes
CategoryT78Adverse effects, not elsewhere classified
This CodeT78.49XAOther allergy, initial encounter

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.

CCSR INJ031
Allergic reactions
Default principal diagnosis: inpatient Yes · outpatient Yes

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 T78.49XA to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
995.3 Allergy, unspecified
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T78.49XAOverview

Is T78.49XA (Other allergy) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other allergy, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T78.49XA mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for other allergy, such as an emergency visit or first evaluation.

What MS-DRG does T78.49XA group to?

When other allergy, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 915, 916, with relative weights from 0.6663 to 1.6816 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of T78.49XA?

Under the General Equivalence Mappings, other allergy, initial encounter converts to ICD-9-CM 995.3 (allergy, unspecified). 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.