T78.4Other and unspecified allergy

T78.4 is the ICD-10-CM diagnosis code for other and unspecified allergy. It belongs to category T78 (adverse effects, not elsewhere classified), block T66-T78 (other and unspecified effects of external causes) and chapter 19 (injury, poisoning and certain other consequences of external causes). It is a header code, so it can't be reported by itself; one of its 3 subcodes must be used instead.

Within T78, choose T78.4 (Other and unspecified allergy) only when documentation doesn't support a more specific option: anaphylactic reaction due to food (T78.0), other adverse food reactions, not elsewhere classified (T78.1), anaphylactic shock, unspecified (T78.2), Angioneurotic edema (T78.3) and other adverse effects, not elsewhere classified (T78.8).

Codes in this range require a 7th character: A for initial encounter, D for subsequent encounter and S for sequela. Use placeholder "X" characters to fill any empty positions before the 7th character.

Don't report T78.4 together with the conditions in its Excludes1 note: allergic diarrhea (K52.29), allergic gastroenteritis and colitis (K52.29), dermatitis (L23-L25, L27.-), food protein-induced enterocolitis syndrome (K52.21) and 2 more.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.