T78.02 Anaphylactic reaction due to shellfish (crustaceans)

Name of the Condition

• Anaphylactic reaction due to shellfish (crustaceans) (ICD-10 Code: T78.02)

Summary

This code is used to document an anaphylactic reaction specifically triggered by shellfish belonging to the crustacean family. Anaphylaxis is a severe, potentially life-threatening allergic reaction that requires immediate medical attention. The code applies when the reaction is directly linked to crustacean shellfish exposure and meets clinical criteria for anaphylaxis.

Causes

Anaphylactic reactions due to crustacean shellfish occur when the immune system overreacts to proteins in shellfish such as shrimp, crab, lobster, or crayfish. The reaction is mediated by immunoglobulin E (IgE) antibodies, which release histamine and other chemicals, leading to rapid onset of symptoms. Even trace amounts of shellfish can trigger a reaction in sensitive individuals.

Risk Factors

• Previous history of shellfish allergy or anaphylaxis
• Family history of allergic conditions
• Asthma or other atopic diseases
• Exposure to crustacean shellfish or cross-contaminated foods
• Delayed administration of epinephrine during prior reactions

Symptoms

• Rapid onset of hives, itching, or swelling (especially of the lips, tongue, or throat)
• Difficulty breathing, wheezing, or stridor
• Drop in blood pressure (hypotension) or dizziness
• Nausea, vomiting, or abdominal cramps
• Loss of consciousness or confusion

Diagnosis

Diagnosis is based on clinical presentation and patient history. Key criteria include acute onset of symptoms after shellfish exposure, involvement of the skin, respiratory, cardiovascular, or gastrointestinal systems, and exclusion of other causes. Specific IgE testing or skin prick tests may confirm sensitization, but clinical correlation is essential.

Treatment Options

• Immediate administration of epinephrine (first-line treatment)
• Antihistamines or corticosteroids to manage residual symptoms
• Oxygen therapy for respiratory distress
• Intravenous fluids for hypotension
• Monitoring in a medical facility for potential biphasic reactions

Prognosis and Follow-Up

With prompt treatment, most patients recover fully. However, recurrence is possible with re-exposure. Follow-up includes referral to an allergist for confirmatory testing, education on avoidance, and prescription of an epinephrine auto-injector. Long-term management focuses on strict avoidance of crustacean shellfish and emergency preparedness.

Complications

• Respiratory failure requiring mechanical ventilation
• Cardiovascular collapse
• Asphyxiation from airway swelling
• Biphasic reactions (recurrence of symptoms hours after initial treatment)
• Anxiety or post-traumatic stress related to the event

Lifestyle & Prevention

• Strict avoidance of crustacean shellfish and cross-contaminated foods
• Reading food labels carefully for hidden shellfish ingredients
• Informing restaurants and food handlers about the allergy
• Carrying an epinephrine auto-injector at all times
• Wearing medical identification (e.g., bracelet) indicating the allergy

When to Seek Professional Help

Seek immediate medical attention if symptoms of anaphylaxis occur, such as difficulty breathing, swelling of the throat, dizziness, or loss of consciousness. Even if symptoms improve after epinephrine, emergency care is necessary to monitor for delayed reactions.

Tips for Medical Coders

This code is specific to anaphylactic reactions due to crustacean shellfish. Documentation should clearly link the reaction to shellfish exposure and confirm clinical criteria for anaphylaxis. Avoid using this code for non-anaphylactic allergic reactions or reactions to other shellfish types (e.g., mollusks). Ensure the medical record supports the diagnosis to justify code assignment.