T78.121A — Other adverse food reaction due to egg with reactivity to baked egg, initial encounter
Is T78.121A billable?
Yes — T78.121A is billable for FY2027. T78.121A is a valid, billable ICD-10-CM code at the highest level of specificity in its branch. T78.121A may be submitted for encounters from October 1, 2026 through September 30, 2027.
T78.121A at a glance
| Code | T78.121A |
|---|---|
| Description | Other adverse food reaction due to egg with reactivity to baked egg, initial encounter |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
| 7th character "A" | initial encounter |
What does the 7th character "A" mean in T78.121A?
In T78.121A, the 7th character A means initial encounter. The 7th character is required for T78.121A to be a valid, complete code.
Same condition, different episode of care — switch the 7th character:
What Medicare edits apply to T78.121A?
The Medicare Code Editor screens inpatient claims before they are grouped. These edits name T78.121A directly.
CMS will reject this code as the principal diagnosis on an inpatient claim. It describes something other than the condition chiefly responsible for the admission.
Which MS-DRGs does T78.121A group to?
T78.121A sits in MDC 21 and helps define the logic of 2 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 922Other Injury, Poisoning and Toxic Effect Diagnoses with MCCmedical
- 923Other Injury, Poisoning and Toxic Effect Diagnoses without MCCmedical
How is T78.121A listed in the Alphabetic Index?
The Alphabetic Index lists these routes under T78.121, the nearest indexed parent of T78.121A. Use them to find the family, then select the specific code.
- Allergy, allergic › eggs › adverse reaction NEC › with › reactivity to baked egg (reaction) (to)
Excludes1 — never code together
The conditions below can never be reported together with T78.121A on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
- Other adverse food reaction due to egg with tolerance to baked egg (T78.120)
Excludes1 — never code together — inherited from T78.1
The conditions below can never be reported together with T78.121A on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
Excludes1 — never code together — inherited from T78.121
The conditions below can never be reported together with T78.121A on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
- Other adverse food reaction due to egg with tolerance to baked egg (T78.120)
Use additional code — inherited from Chapter 19
Report an additional code alongside T78.121A to fully describe the condition. T78.121A is sequenced first.
- code to identify any retained foreign body, if applicable (Z18.-)
Use additional code — inherited from T78.1
Report an additional code alongside T78.121A to fully describe the condition. T78.121A is sequenced first.
- code to identify the type of reaction, if applicable
Excludes2 — not included here — inherited from Chapter 19
The conditions below are not part of T78.121A, but a patient may have both at the same time. When documentation supports it, T78.121A and the excluded code may both be reported.
Excludes2 — not included here — inherited from T78
The conditions below are not part of T78.121A, but a patient may have both at the same time. When documentation supports it, T78.121A and the excluded code may both be reported.
- complications of surgical and medical care NEC (T80-T88)
Excludes2 — not included here — inherited from T78.1
The conditions below are not part of T78.121A, but a patient may have both at the same time. When documentation supports it, T78.121A and the excluded code may both be reported.
Code also — inherited from T66-T78
Two codes may be needed to describe the condition fully. Whether T78.121A is sequenced first depends on the reason for the encounter.
- , 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-)
How long has T78.121A existed?
T78.121A first appears in FY2026.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.