2025 ICD-10-CM code T78.40
Allergic reaction not otherwise specified (NOS).
The medical necessity for coding T78.40 hinges on the documentation of an allergic reaction. The documentation should support the clinical findings consistent with an allergic response and provide sufficient detail to justify the diagnosis.
The clinical responsibility includes documenting the patient's history of allergen exposure, conducting a thorough physical examination to assess the severity of the reaction, and ordering appropriate laboratory tests (if necessary) to confirm the diagnosis and rule out other conditions.
- Injury, poisoning and certain other consequences of external causes (T07-T88)
- T78.40 is under the broader category of T78 (Other and unspecified effects of external causes) and the larger chapter of external causes of morbidity.
In simple words: This code is used when someone has an allergic reaction, but the doctors don't know exactly what kind of reaction it is.
This code classifies an allergic reaction where the specific type of reaction is not specified or cannot be determined.It encompasses a broad range of allergic responses, both local and systemic, resulting from exposure to an allergen.The code is used when more specific allergic reaction codes are not applicable due to insufficient information or the non-specificity of the reaction.
Example 1: A patient presents to the emergency department with generalized urticaria, angioedema, and dyspnea after eating shellfish.T78.40 is coded if the exact type of allergic reaction (e.g., anaphylaxis) is unclear or not definitively established based on the clinical presentation and investigations.Additional codes from Chapter XX would specify the cause (shellfish)., A patient develops localized skin rash after coming into contact with poison ivy. If there is uncertainty regarding the specific allergic manifestation (e.g., allergic contact dermatitis vs. irritant contact dermatitis), T78.40 might be used. The specific cause would be added as a secondary code., A patient experiences generalized itching and swelling after taking a new medication.Without a definitive diagnosis of the type of allergic reaction (e.g., drug allergy, serum sickness), T78.40 can be used. An additional code from Chapter XX would specify the medication involved.
Detailed history of allergen exposure, including timing, route, and quantity. Thorough physical examination documenting the specific symptoms and severity of the allergic reaction. Relevant laboratory tests (e.g., allergy testing, complete blood count, etc.) if performed. Treatment administered and patient response.
** This code is often used as a placeholder until a more definitive diagnosis of the specific type of allergic reaction is available.Always ensure that the clinical documentation adequately supports the use of this code.
- Payment Status: Active
- Specialties:Allergy and immunology, emergency medicine, family medicine
- Place of Service:Office, Emergency Room - Hospital, Urgent Care Facility, Inpatient Hospital