ICD-10-CM > S00-T88 > T66-T78 > T78 > T78.4 > T78.40 T78.40 Allergy, unspecified Non-Billable/Non-Specific Applicable To Allergic reaction NOSHypersensitivity NOS Codes T78.40XA..., initial encounterT78.40XD..., subsequent encounterT78.40XS..., sequela