History of Present Illness for Allergic Reactions
When documenting the HPI for a patient with an allergic reaction, immediately establish the temporal relationship between allergen exposure and symptom onset, then systematically document involvement of skin/mucosa, respiratory, cardiovascular, and gastrointestinal systems to determine if diagnostic criteria for anaphylaxis are met.
Critical Timing and Exposure Information
Start by documenting:
- Exact time of symptom onset (anaphylaxis typically occurs within minutes to several hours of exposure) 1
- Suspected allergen or trigger and route of exposure (ingestion, injection, inhalation, contact)
- Time interval between exposure and first symptom - this temporal relationship is essential for diagnosis 2
Systematic Symptom Documentation by Organ System
Document the presence or absence of symptoms in each system, as anaphylaxis diagnosis requires specific combinations 1:
Skin/Mucosal Involvement
- Generalized hives, pruritus, flushing
- Swelling of lips, tongue, or uvula
- Note: skin symptoms may be absent in up to 20% of anaphylaxis cases, particularly after insect stings 1
Respiratory System
- Shortness of breath, wheezing, cough
- Stridor (upper airway involvement)
- Hypoxemia or respiratory distress
- In children, respiratory compromise is more likely than hypotension 1
Cardiovascular System
- Dizziness, syncope, or presyncope
- Chest pain or palpitations
- Document actual blood pressure if available:
- Adults: systolic BP <90 mmHg or >30% decrease from baseline
- Children 1 month-1 year: <70 mmHg
- Children 1-10 years: <(70 mmHg + [2 × age])
- Children 11-17 years: <90 mmHg 1
- Tachycardia may be the initial manifestation of shock in children 1
Gastrointestinal System
- Crampy abdominal pain
- Nausea, vomiting
- Diarrhea
Progression and Treatment Response
Document:
- Rapidity of symptom progression (acute onset over minutes to hours is characteristic) 1
- Any treatments already administered (antihistamines, epinephrine, corticosteroids) and response
- Whether symptoms have resolved, are ongoing, or are worsening
- Even if symptoms have completely resolved before arrival, document if they previously met diagnostic criteria - this still warrants an anaphylaxis diagnosis 1
Risk Factors for Severe Reactions
Include in the HPI:
- History of previous allergic reactions or anaphylaxis
- Known allergies and prior allergy testing
- Asthma or other atopic conditions (increases severity risk) 2, 3
- Current medications, particularly beta-blockers or ACE inhibitors (can worsen anaphylaxis)
- Family history of allergic disease 3
Environmental and Occupational Context
Document:
- Location where reaction occurred (home, restaurant, workplace, outdoors)
- Activities immediately preceding symptom onset
- Any similar previous episodes in similar circumstances 4
Common Pitfalls to Avoid
- Do not dismiss the diagnosis if skin symptoms are absent - some patients present with isolated respiratory or cardiovascular symptoms, particularly after insect stings 1
- Do not overlook biphasic reactions - document any history of symptom recurrence 1-78 hours after initial resolution, as this occurs in 4-5% of cases 1
- In children, do not wait for hypotension - respiratory symptoms and tachycardia typically precede blood pressure changes 1
- For drug reactions, document all medications taken in the preceding hours to days, not just those taken immediately before symptom onset 5, 6
The clinical history remains the cornerstone of allergic disease diagnosis 2, 7, and a detailed HPI following this structure will guide appropriate immediate management and subsequent allergy testing decisions.