What is the proper assessment and treatment approach for a patient suspected of having an allergic reaction?

Assessment of Allergic Reactions

Use the systematic ABCDE (Airway, Breathing, Circulation, Disability, Exposure) approach to assess all suspected allergic reactions, focusing on identifying life-threatening features that require immediate epinephrine administration. 1

Clinical Grading System

Apply the modified Ring and Messmer scale to grade reaction severity and guide treatment decisions: 1

• Grade I (Mild): Generalized erythema, extensive urticaria, or angioedema affecting skin/mucosa only—no epinephrine required 1
• Grade II (Moderate): Multi-organ involvement with skin/mucosal changes PLUS moderate hypotension, tachycardia, moderate bronchospasm, or gastrointestinal symptoms—epinephrine indicated 1
• Grade III (Severe): Life-threatening hypotension, tachycardia or bradycardia with/without arrhythmia, severe bronchospasm, with or without skin changes—immediate epinephrine required 1
• Grade IV (Critical): Cardiac or respiratory arrest—immediate CPR and epinephrine 1

Systematic Assessment Components

Airway Evaluation

• Assess for: Lip/tongue/uvula swelling, pharyngeal/laryngeal edema, stridor, hoarseness, difficulty swallowing 1
• Critical pitfall: Soft tissue swelling from airway manipulation during intubation can mimic angioedema; check if tryptase is elevated to differentiate 1

Breathing Assessment

• Assess for: Dyspnea, wheeze, bronchospasm, reduced peak expiratory flow, hypoxemia, respiratory distress, use of accessory muscles 1
• Important distinction: Isolated bronchospasm without tryptase elevation may indicate undiagnosed asthma, aspiration, or airway hyperreactivity rather than true allergy 1

Circulation Assessment

• Assess for: Hypotension (systolic BP <90 mmHg or >30% decrease from baseline), tachycardia, bradycardia, weak/thready pulse, syncope, collapse, incontinence 1
• Critical consideration: Isolated hypotension without tryptase elevation has multiple non-allergic causes including drug effects, bleeding, or other shock states 1

Skin/Mucosal Examination

• Assess for: Generalized urticaria, flushing, pruritus, angioedema, erythema distribution and extent 1
• Warning signs for severe cutaneous reactions: Vesicles/crusts, grey-violaceous lesions, painful/burning skin, hemorrhagic erosions, skin detachment (Stevens-Johnson syndrome/toxic epidermal necrolysis), pustules, purpura, facial edema with fever >38.5°C 1
• Key distinction: Isolated skin symptoms without tryptase elevation often represent non-specific histamine release (especially with opioids) rather than true IgE-mediated allergy 1

Gastrointestinal Assessment

• Assess for: Severe crampy abdominal pain, repetitive vomiting, diarrhea 1

Diagnostic Laboratory Testing

Serum Tryptase Measurement

Obtain three timed samples to confirm mast cell degranulation: 1, 2

• Sample 1: As soon as feasible after reaction onset (do not delay resuscitation) 1, 2
• Sample 2: 1-2 hours after symptom onset 1, 2
• Sample 3: Baseline sample at ≥24 hours post-reaction or during convalescence 1, 2

Interpretation criteria: An increase above 1.2 × baseline + 2 μg/L confirms mast cell degranulation 2, 3

Critical pitfall: Normal tryptase does NOT exclude anaphylaxis—reactions can occur through basophil or complement activation pathways without tryptase elevation 3

Differential Diagnosis Considerations

Single-Organ System Involvement

If symptoms arise from only one organ system AND tryptase is not elevated compared to baseline, consider non-allergic causes: 1

• Isolated hypotension: Anesthetic drug effects, neuraxial blockade, bleeding, other shock types, tricyclic antidepressants 1
• Isolated bronchospasm: Uncontrolled asthma/COPD, inadequate anesthesia depth, tube malposition, aspiration 1
• Isolated angioedema: ACE inhibitor-induced (onset 1-8 hours post-surgery), hereditary angioedema, airway manipulation trauma 1

High-Risk Patient Populations

Patients with these conditions require heightened vigilance as they may have reactions clinically indistinguishable from IgE-mediated anaphylaxis: 1

• Systemic mastocytosis or clonal mast cell disorders: Triggered by non-specific mechanical factors (temperature, stress, histamine-releasing drugs) 1
• Chronic urticaria/angioedema: May have exacerbations mimicking allergic reactions 1
• Cold urticaria: Can develop reactions with cooled medications 1

Documentation Requirements

Meticulously document all exposures and timing: 2

• Exact timing of all drug/substance administrations relative to symptom onset 2
• All medications, IV fluids, colloids, latex exposure, antiseptics (especially chlorhexidine) 1, 2
• Symptom progression timeline 2
• Treatment response and doses administered 2
• Tryptase sample collection times 2

Post-Assessment Actions

All Grade II-IV reactions and Grade I reactions with generalized urticaria/erythema require: 2

• Referral to specialized allergy clinic for formal investigation 4-6 weeks post-reaction 2
• Written documentation provided to patient detailing exposures to avoid until testing completed 2
• Testing should include skin testing, specific IgE antibody testing, and potentially drug provocation testing 2