T78.129A vs T78.129S

T78.129A (Other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, initial encounter) compared with T78.129S (Other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela), from the official CMS tabular data. T78.129A and T78.129S code the same injury at a different phase of treatment.

Relationship

Review

Encounter relationship

T78.129A

Initial encounter

Other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, initial encounter

↔

T78.129S

Sequela

Other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela

Same underlying diagnosis, different encounter phase.

The 7th character records the phase of care for the encounter being coded, so a single encounter takes one of these characters, not several. Review whether both phases belong on the same episode of care.

Source: ICD-10-CM Official Guidelines, Section I.C.19.a

Can these codes be reported together?

Same injury, other encounter phase. T78.129A and T78.129S code the same injury at a different phase of treatment, set by the 7th character.

The 7th character records the type of care given at the encounter being coded (ICD-10-CM Official Guidelines, Section I.C.19.a), so one encounter takes one of these, not both.

Side by side

	T78.129AOther adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, initial encounter	T78.129SOther adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela
Billing status	Billable	Billable
Classification	S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88)	S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88)
Definition	Other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, initial encounter is a billable ICD-10-CM diagnosis code (T78.129A).	Other adverse food reaction due to egg with baked egg tolerance/reactivity, unspecified, sequela is a billable ICD-10-CM diagnosis code (T78.129S).
7th character	The appropriate 7th character is to be added to each code from category T78	The appropriate 7th character is to be added to each code from category T78
Use additional code	code to identify the type of reaction, if applicable	code to identify the type of reaction, if applicable

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Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources