2027 ICD-10-CM Diagnosis Code T78.49XAOther allergy, initial encounter
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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 915 through 916. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Allergic reactions.
Code Identity
Code Classification
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 due to 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
- Severe asthma with fungal sensitization
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 2027, published by CMS and the National Center for Health Statistics.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to T78.49XA: its own notes plus those printed at T78.4, T78, block T66-T78, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify any retained foreign body, if applicable (Z18.-)
Code Also
A second code may be needed to fully describe the condition; the note gives no sequencing direction.
- if applicable, place of occurrence, such as:
- highway rest stop (Y92.523)
- school (private) (public) (state) as the place of occurrence of the external cause (Y92.21-)
- service areas as the place of occurrence of the external cause (Y92.52-)
- single-family non-institutional (private) house as the place of occurrence of the external cause (Y92.01-)
- transport vehicle as the place of occurrence of the external cause (Y92.81-)
Notes
General instructions on how these codes are used.
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from category T78
- Ainitial encounter this code
- Dsubsequent encounter
- Ssequela
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name T78.49XA, its category, or a range that includes it.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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.
Code HistoryHistory
Questions About T78.49XAOverview
What is the ICD-10 code for other allergy, initial encounter?
The ICD-10-CM code for other allergy, initial encounter is T78.49XA (sometimes written as T7849XA). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
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, 2026 through September 30, 2027.
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 0.6926 to 1.6559 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T78.49XA be reported with K52.29?
Not as a rule. The Excludes1 note at T78.4, which applies to T78.49XA, lists "allergic diarrhea (K52.29)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
