T78.02XD Anaphylactic reaction due to shellfish (crustaceans), subsequent encounter

ICD-10-CM T78.02XD: Anaphylactic reaction due to shellfish (crustaceans), subsequent encounter

ICD-10-CM code T78.02XD represents an anaphylactic reaction due to shellfish crustaceans for a subsequent encounter. Official terminology sources confirm this exact code and its subsequent encounter designation. Payer coding articles list this code alongside initial encounter and sequela variants. Clinical literature establishes that shellfish allergy involves severe immune reactions to crustacean and mollusk proteins. 1 2 4 5

Plain-language overview

Shellfish allergy involves immune reactions to crustacean and mollusk proteins upon consumption or inhalation, and it is one of the most severe and persistent food allergies affecting approximately one to three percent of the general population worldwide. 1

What this code represents

The ICD-10-CM code T78.02XD is officially labeled as anaphylactic reaction due to shellfish crustaceans, subsequent encounter by terminology sources. 2 3

Coding details

Payer billing and coding articles list T78.02XD for a subsequent encounter alongside T78.02XA for an initial encounter and T78.02XS for a sequela. 4 5

Documentation considerations

Clinical literature notes that shellfish generally refers to both groups of edible crustaceans such as shrimp, crab, and lobster and mollusks such as oyster, mussels, snails, octopus, and squid. 1

What the sources add

Terminology sources from the National Library of Medicine and the National Cancer Institute provide the official code display, while Centers for Medicare and Medicaid Services articles provide billing and coding context listing the code variants. 2 3 4 5

Clinical literature from PubMed Central establishes that shellfish allergy is rarely outgrown and a high risk of severe allergic reactions persists throughout life, whereas payer sources do not provide this clinical context. 1 4 5

Clinical context

The major allergen in shellfish allergy is tropomyosin, which exhibits significant cross-reactivity among various types of shellfish including crustaceans, mollusks, and cephalopods, and also with mites and other arthropods. 1

Coverage and utilization context

Centers for Medicare and Medicaid Services billing and coding articles on allergy testing include T78.02XD in their code listings. 4 5

Sources

1. Advances in Shellfish Allergy Therapy: From Current Approaches to Future Strategies — pmc.ncbi.nlm.nih.gov; accessed 2026-07-25.
2. Browse Code Systems — vsac.nlm.nih.gov; accessed 2026-07-25.
3. EVS Explore — evsexplore.semantics.cancer.gov; accessed 2026-07-25.
4. Article - Billing and Coding: Allergy Testing (A57531) — cms.gov; accessed 2026-07-25.
5. Article - Billing and Coding: Allergy Testing (A56558) — cms.gov; accessed 2026-07-25.