ICD-10-CM T78.40 is the diagnosis code for Allergy, unspecified. This code falls under the section "Other and unspecified effects of external causes" within Chapter 19 — Injury, poisoning and certain other consequences of external causes (S00-T88). It is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes. Medical coders and healthcare providers use this code to document and classify diagnoses in electronic health records, insurance claims, and clinical databases.
Understanding where T78.40 sits in the ICD-10-CM classification helps ensure proper coding:
Yes, T78.40 is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes.
T78.40 is the ICD-10-CM diagnosis code for "Allergy, unspecified". It is used by healthcare providers to classify and document this condition in medical records and insurance claims.
The parent code of T78.40 is T78.4 ("Other and unspecified allergy"). T78.40 provides a more specific classification within this category.
T78.40 is located in Section T66-T78 — "Other and unspecified effects of external causes" within Chapter 19 of the ICD-10-CM Tabular List.
Use T78.40 when the patients documented diagnosis matches "Allergy, unspecified" and the clinical documentation supports this level of specificity. Always verify with the latest ICD-10-CM guidelines and payer requirements.
The ICD-10-CM code for Allergy, unspecified is T78.40.
Yes, T78.40 can be used as a primary diagnosis code since it is billable and specific.
T78.40 is in Chapter 19 of the ICD-10-CM Tabular List.
Yes, T78.40 is a valid ICD-10-CM code for the 2026 fiscal year, subject to official CMS updates.