ICD-10-CM 2027 diagnosis code
T78.49XAOther allergy, initial encounter
T78.49XA is a valid, billable ICD-10-CM code for other allergy, initial encounter. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.
Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data
About T78.49XA
T78.49XA is the ICD-10-CM diagnosis code for other allergy, initial encounter. It belongs to category T78 (adverse effects, not elsewhere classified), block T66-T78 (other and unspecified effects of external causes) and chapter 19 (injury, poisoning and certain other consequences of external causes). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.
The 7th character "A" means initial encounter: use it while the patient is receiving active treatment for the condition.
It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.
In MS-DRG v44.0, it is part of the grouping logic for DRG 915 (Allergic Reactions with MCC, relative weight 1.6558) and DRG 916 (Allergic Reactions without MCC, relative weight 0.6928), in MDC 21 (Injuries, Poisonings and Toxic Effects of Drugs), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.
Before ICD-10, this condition was coded in ICD-9-CM as 995.3 (allergy, unspecified, not elsewhere classified).
7th character
Ainitial encounter
Other encounter types for T78.49:
Notes that apply from higher levels
Instructions written at a parent level also apply to T78.49XA.
Broader instructions also apply from T66-T78 Other and unspecified effects of external causes and Chapter 19: Injury, poisoning and certain other consequences of external causes.
MS-DRG v44.0 grouping
All DRGs →Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.
MDC 21 · Injuries, Poisonings and Toxic Effects of Drugs
ICD-9-CM equivalent
Converter →- 995.3Allergy, unspecified, not elsewhere classifiedapproximate
From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.
Code history
- 2016
- 2017
- 2018
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
- 2027
- FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
- No changes since FY2016.
Common questions about T78.49XA
Is T78.49XA billable?
- Yes. T78.49XA is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
What does the "A" at the end of T78.49XA mean?
- It is the 7th character for initial encounter. Per the official guidelines, use it while the patient is receiving active treatment for the condition.
Can T78.49XA be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict T78.49XA as a principal diagnosis.
Is T78.49XA a CC or MCC?
- No. T78.49XA is neither a CC nor an MCC under MS-DRG v44.0.
What DRG does T78.49XA group to?
- T78.49XA is used in the MS-DRG v44.0 logic for MS-DRG 915 (Allergic Reactions with MCC) and MS-DRG 916 (Allergic Reactions without MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.
What is the ICD-9 code for T78.49XA?
- The CMS General Equivalence Mappings map T78.49XA to ICD-9-CM 995.3.