2026 ICD-10-CM Diagnosis Code T78.129SOther adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela
T78.129S is a billable ICD-10-CM diagnosis code for other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, 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 not accepted as a principal diagnosis by the Medicare Code Editor and exempt from POA reporting. Coders also document this condition as allergic reaction caused by egg protein.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T78.129S.
Present on Admission (POA)Billing
T78.129S 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 reaction caused by egg protein
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.
Code History & ChangesHistory
New Code T78.129S was added to the ICD-10-CM code set for FY 2026, effective October 1, 2025.
Replacement T78.129S replaces the following previously assigned code(s):
- T78.1XXS - Oth adverse food reactions, NEC, sequela
Questions About T78.129SOverview
Is T78.129S a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character S in T78.129S mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified itself has resolved, not the original event.
What MS-DRG does T78.129S group to?
On inpatient claims, other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela maps to MS-DRG 922, 923, with relative weights from 1.0177 to 1.7494 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T78.129S be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
Is T78.129S 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 adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela on inpatient claims.
