An ICD-10 allergic reaction code captures hypersensitivity events across pharmaceuticals, foods, and environmental triggers. Accurate coding ensures consistent reporting, safer care transitions, and clearer population health insights for clinicians and payers.
This overview explains how to locate the right codes, link them to causative agents, and apply them in both clinical documentation and billing workflows.
| Code | Allergen Type | Reaction Body System | Laterality / Site | Status or Context |
|---|---|---|---|---|
| T78.0 | Drugs and medicaments | Multi-system, anaphylaxis | Generalized | Adverse effect, initial encounter |
| T78.1 | Food | Skin, respiratory, gastrointestinal | Generalized | Adverse effect, initial encounter |
| T78.2 | Late effect external cause | Variants such as asthma or dermatitis | Organ-specific | Initial encounter for late effect |
| T78.3 | Contact dermatitis | Skin | Site-specific, eczematous | Initial encounter, irritant or allergic |
| T78.4 | Other and unspecified | Variable by documentation | Dependent on detail | Used when agent or reaction is not specified |
T78.0 Drug And Medicament Reactions In ICD-10
T78.0 is the primary code for an immediate hypersensitivity response to pharmaceuticals. It supports specificity when clinicians document drug name, reaction type, and temporal relationship to administration.
Use additional characters for laterality and severity when they are provided in the health record to optimize data quality and specificity.
T78.1 Food And Dietary Protein Reactions
T78.1 applies to IgE-mediated responses to foods, including peanuts, shellfish, and other allergens. Document the specific ingested agent and reaction features to improve clinical decision support and patient education.
Coders should verify whether the event represents a true allergy versus an intolerance, because management pathways and coding differ significantly.
T78.3 Contact Dermatitis And Topical Agents
T78.3 is designated for allergic contact dermatitis caused by topical medications, cosmetics, or occupational exposures. It highlights skin-focused reactions with identifiable external triggers.
Capture laterality such as left hand or bilateral lower extremities when documentation supports it, enabling more precise tracking and workplace safety insights.
Late Effects And External Cause Context
T78.2 is used when sequelae of prior hypersensitivity persist after the acute episode has resolved. This might include chronic urticaria or ongoing asthma related to earlier triggers.
Sequence these codes with care, ensuring that the late effect is appropriately linked to the original causative agent and encounter type.
Key Recommendations For Clinical Documentation And Coding
- Specify the allergen, reaction type, and anatomical site in the health record to enable precise code assignment.
- Differentiate true hypersensitivity from intolerance or non-allergic adverse events during documentation and coding.
- Sequence codes to reflect the primary reason for the encounter and the timing of the allergic event.
- Include status character for initial, subsequent, or sequela encounters to align with the episode of care.
- Leverage laterality and severity details to improve data quality, safety monitoring, and population health insights.
FAQ
Reader questions
How do I choose between T78.0 and T78.1 for a patient with a reaction after taking an antibiotic and eating shellfish?
Assign T78.0 for the antibiotic-related event and T78.1 for the shellfish-related event, documenting each agent and reaction separately to maintain specificity.
Can T78.3 be used for a reaction to a transdermal patch applied for pain management?
Yes, T78.3 is appropriate for allergic contact dermatitis caused by a transdermal medication or patch, provided the clinical documentation links the dermatitis to the patch ingredient.
What if the record only states allergic reaction without specifying the agent or route?
Report T78.4, Allergen and reaction unspecified, when the health record lacks details needed to assign a more specific code under T78.0–T78.3.
Should bilateral symptoms such as rash on both arms be flagged as unilateral or bilateral in the encounter note?
Capture laterality accurately as bilateral when the documentation describes symmetric involvement on both sides, supporting richer analytics and care planning.