2026 ICD-10-CM Diagnosis Code T78.121A
Other adverse food reaction due to egg with reactivity to baked egg, initial encounter
- ICD-10-CM Code:
- T78.121A
- ICD-10 Code for:
- Other advrs food react d/t egg with rct to baked egg, init
- Is Billable?
- Yes - Valid for Submission
- Code Navigator:
T78.121A is a billable diagnosis code used to specify a medical diagnosis of other adverse food reaction due to egg with reactivity to baked egg, initial encounter. The code is valid during the current fiscal year for the submission of HIPAA-covered transactions from October 01, 2025 through September 30, 2026.
This code describes a circumstance which influences the patient's health status but not a current illness or injury. The code is unacceptable as a principal diagnosis.
T78.121A is an initial encounter code, includes a 7th character and should be used while the patient is receiving active treatment for a condition like other adverse food reaction due to egg with reactivity to baked egg. According to ICD-10-CM Guidelines an "initial encounter" doesn't necessarily means "initial visit". The 7th character should be used when the patient is undergoing active treatment regardless if new or different providers saw the patient over the course of a treatment. The appropriate 7th character codes should also be used even if the patient delayed seeking treatment for a condition.
Coding Guidelines
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 aplicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
New 2026 ICD-10-CM Code
T78.121A is new to ICD-10-CM code set for the FY 2026, effective October 1, 2025. The National Center for Health Statistics (NCHS) has published an update to the ICD-10-CM diagnosis codes which became effective October 1, 2025. This is a new and revised code for the FY 2026 (October 1, 2025 - September 30, 2026).
Code Edits
The Medicare Code Editor (MCE) detects errors and inconsistencies in ICD-10-CM diagnosis coding that can affect Medicare claim validity. These Medicare code edits help medical coders and billing professionals determine when a diagnosis code is not appropriate as a principal diagnosis, does not meet coverage criteria. Use this list to verify whether a code is valid for Medicare billing and to avoid claim rejections or denials due to diagnosis coding issues.
Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.
Replacement Code
T78121A replaces the following previously assigned ICD-10-CM code(s):
- T78.1XXA - Oth adverse food reactions, not elsewhere classified, init
Code History
- FY 2026 - Code Added, effective from 10/1/2025 through 9/30/2026
