2027 ICD-10-CM Diagnosis Code T78.120SOther adverse food reaction due to egg with tolerance to baked egg, sequela

ICD-10-CM Codes›S00–T88›T66-T78›T78

ICD-10-CM T78.120S
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

T78.120S is a billable ICD-10-CM diagnosis code for other adverse food reaction due to egg with tolerance to baked egg, 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 2027 (October 1, 2026 through September 30, 2027) 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury, sequela.

Code Identity

ICD-10-CM Code
T78.120S
Billable Status
Yes — Valid for Submission
Code Describes
Other adverse food reaction due to egg with tolerance to baked egg, sequela
Short Description
Other ad food react d/t egg with tolerance to bkd egg, sqla
Parent Code
T78.120
Other adverse food reaction due to egg with tolerance to baked egg

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT66-T78Other and unspecified effects of external causes
CategoryT78Adverse effects, not elsewhere classified
This CodeT78.120SOther adverse food reaction due to egg with tolerance to baked egg, sequela

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T78.120S.

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.

Present on Admission (POA)Billing

T78.120S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Other and unspecified effects of external causes (T66-T78).

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 2027, published by CMS and the National Center for Health Statistics.

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to T78.120S: its own notes plus those printed at T78.120, T78.1, T78, block T66-T78, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From T78.120 Other adverse food reaction due to egg with tolerance to baked egg applies to 3 codes
  • Other adverse food reaction due to egg with reactivity to baked egg (T78.121)
From T78.1 Other adverse food reactions, not elsewhere classified applies to 21 codes
  • anaphylactic reaction or shock due to adverse food reaction (T78.0-)
  • anaphylactic reaction due to food (T78.0-)
  • bacterial food borne intoxications (A05.-)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From T78.1 Other adverse food reactions, not elsewhere classified applies to 21 codes
  • allergic and dietetic gastroenteritis and colitis (K52.29)
  • allergic rhinitis due to food (J30.5)
  • dermatitis due to food in contact with skin (L23.6, L24.6, L25.4)
  • dermatitis due to ingested food (L27.2)
  • food protein-induced enterocolitis syndrome (K52.21)
  • food protein-induced enteropathy (K52.22)
From T78 Adverse effects, not elsewhere classified applies to 81 codes
  • complications of surgical and medical care NEC (T80-T88)
From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From T78.1 Other adverse food reactions, not elsewhere classified applies to 21 codes
  • code to identify the type of reaction, if applicable
From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • code to identify any retained foreign body, if applicable (Z18.-)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From Block T66-T78 Other and unspecified effects of external causes applies to 456 codes
  • 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-)

Notes

General instructions on how these codes are used.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
  • The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.

7th Character

Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.

From T78 Adverse effects, not elsewhere classified applies to 81 codes
  • The appropriate 7th character is to be added to each code from category T78
Values for category T78 Encounter: Initial, Subsequent, Sequela
  • Ainitial encounter
  • Dsubsequent encounter
  • Ssequela this code

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name T78.120S, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming T78.120S: they are not reported together with it, unless the two conditions are unrelated.

  • T75 Other and unspecified effects of other external causes
    adverse effects NEC (T78.-) names T78.-, which includes this code
  • T78.121 Other adverse food reaction due to egg with reactivity to baked egg
    Other adverse food reaction due to egg with tolerance to baked egg (T78.120) names T78.120, which includes this code

Excludes2 1

These codes carry an Excludes2 note naming T78.120S: its condition is not part of those codes, and both may be reported when the patient has both.

  • L27 Dermatitis due to substances taken internally
    adverse food reaction, except dermatitis (T78.0-T78.1) names T78.0-T78.1, which includes this code

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INJ073
Injury, sequela
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Food Allergy

A food allergy is an abnormal immune system reaction to certain foods. Your immune system normally protects you from germs. But if you have a food allergy, your immune system mistakenly reacts to certain foods as if they were harmful. This reaction is usually mild. But in some cases, it can be serious or even life-threatening.

The full article covers:

  • What is a food allergy?
  • Who is more likely to develop a food allergy?
  • What are the symptoms of food allergies?
  • How are food allergies diagnosed?
  • What are the treatments for food allergies?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Code History & ChangesHistory

Replacement T78.120S replaces the following previously assigned code(s):

  • T78.1XXS - Oth adverse food reactions, NEC, sequela
FY 2026AddedAdded to the ICD-10-CM code setEffective October 1, 2025.
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About T78.120SOverview

Is T78.120S a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other adverse food reaction due to egg with tolerance to baked egg, sequela on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What does the 7th character S in T78.120S 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 tolerance to baked egg itself has resolved, not the original event.

What MS-DRG does T78.120S group to?

On inpatient claims, other adverse food reaction due to egg with tolerance to baked egg, sequela maps to MS-DRG 923, 922, with relative weights from 0.9980 to 1.6248 depending on complications. Higher weights mean higher Medicare reimbursement.

Can T78.120S 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 tolerance to baked egg, sequela describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

Is T78.120S 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 tolerance to baked egg, sequela on inpatient claims. The code appears in the Other and unspecified effects of external causes (T66-T78) range of the CMS exempt list.