T78.4
Other and unspecified allergy
T78.4 is a non-billable ICD-10-CM code header for other and unspecified allergy. Report a more specific code from it instead. It is part of the FY2027 code set, effective October 1, 2026. The more specific codes under it are T78.40 Allergy, unspecified; T78.41 Arthus phenomenon and T78.49 Other allergy. Its coding notes include a Use additional code instruction, a Code also instruction, 7 Excludes1 entries and 3 Excludes2 entries.
7th characters
Every code below needs one of these (defined at T78).
The appropriate 7th character is to be added to each code from category T78
- Ainitial encounter
- Dsubsequent encounter
- Ssequela
Guidelines tip
From the FY2027 Official Guidelines. ICD10Ref adds no rules of its own.
The 7th character depends on whether the patient is in active treatment, not on who sees the patient. An aftercare Z code is not used for injury aftercare.
Use additional code
Add the listed code as a secondary code, if known.
Also from chapter/block level (1 note)
- code to identify any retained foreign body, if applicable (Z18.-)
Code also
Two codes may be needed to describe the condition. This note gives no sequencing order.
Also from chapter/block level (6 notes)
- , 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-)
Excludes1
Not coded here. The listed conditions generally should not be reported together.
Excludes2
Not included here. Both codes may be reported if the patient has both conditions.
- complications of surgical and medical care NEC (T80-T88)
Also from chapter/block level (2 notes)
- birth trauma (P10-P15)
- obstetric trauma (O70-O71)
Notes
Also from chapter/block level (2 notes)
- 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.