What are the diagnostic criteria for anaphylaxis in a patient with a history of allergies and asthma?

Anaphylaxis Diagnostic Criteria

Anaphylaxis is diagnosed when any ONE of three clinical criteria is met, as established by the NIAID/FAAN consensus and validated in emergency department settings with a positive likelihood ratio of 3.26. 1, 2

The Three Diagnostic Criteria

Criterion 1: Acute onset (minutes to hours) of skin/mucosal involvement PLUS at least one of the following:

• Skin/mucosal tissue involvement: generalized hives, pruritus, flushing, or swollen lips/tongue/uvula 3
• Respiratory compromise: dyspnea, wheeze, bronchospasm, stridor, reduced peak expiratory flow, or hypoxemia 3
• Reduced blood pressure or end-organ dysfunction: hypotonia (collapse), syncope, or incontinence 3

Criterion 2: Two or more of the following occurring rapidly (minutes to hours) after exposure to a likely allergen:

• Skin/mucosal involvement (hives, itch/flush, swollen lips/tongue/uvula) 3
• Respiratory compromise (dyspnea, wheeze, stridor, hypoxemia) 3
• Reduced blood pressure or end-organ dysfunction (hypotonia, syncope, incontinence) 3
• Persistent gastrointestinal symptoms (crampy abdominal pain, vomiting) 3

Criterion 3: Reduced blood pressure alone after exposure to a KNOWN allergen for that specific patient:

• Adults: systolic BP <90 mm Hg or >30% decrease from baseline 3
• Infants (1 month to 1 year): systolic BP <70 mm Hg 3
• Children (1-10 years): systolic BP <(70 mm Hg + [2 × age in years]) 3
• Adolescents (11-17 years): systolic BP <90 mm Hg 3

Critical Clinical Pearls for Patients with Allergies and Asthma

Patients with preexisting asthma are at significantly higher risk for fatal anaphylaxis, particularly if epinephrine administration is delayed. 3 This population requires heightened vigilance because:

• Respiratory symptoms may initially be mistaken for an asthma exacerbation rather than anaphylaxis 4
• The more rapidly symptoms develop after allergen exposure, the more likely the reaction is severe and life-threatening 2
• Tachycardia (even without hypotension) may indicate shock in children, and hypotension may be a late finding 3

Frequency of Clinical Manifestations

Understanding symptom frequency helps recognize anaphylaxis patterns:

• Cutaneous symptoms occur in 90% of cases (urticaria/angioedema 85-90%, flushing 45-55%) 3
• However, 10-20% of anaphylaxis cases have NO skin findings, including many fatal and near-fatal reactions 3
• Respiratory symptoms occur in 40-70% of cases (dyspnea/wheeze 45-50%, upper airway angioedema 50-60%) 3
• Cardiovascular symptoms occur in 30-35% (dizziness, syncope, hypotension) 3
• Gastrointestinal symptoms occur in 25-40% (nausea, vomiting, diarrhea, cramping) 3

Critical Differential Diagnoses to Exclude

Vasovagal reaction is the most common mimic of anaphylaxis and must be distinguished by: 3, 2

• Absence of urticaria, pruritus, or flushing 3, 2
• Bradycardia (not tachycardia) during the event 3, 2
• Pallor, weakness, nausea, vomiting, and diaphoresis without cutaneous allergic manifestations 3

Other important differentials include: 3, 2

• Acute asthma exacerbation (isolated respiratory symptoms without multi-system involvement)
• Panic attack or acute anxiety disorder
• Systemic mastocytosis (recurrent episodes without clear allergen exposure)
• Scombroid fish poisoning (histamine-induced flush resembling sunburn, often affecting multiple diners)
• Hereditary or acquired angioedema (C1 esterase deficiency—presents with angioedema without urticaria or hypotension)

Essential Clinical Assessment Components

When evaluating suspected anaphylaxis, systematically assess: 2

• Level of consciousness (confusion, altered mental status, sense of impending doom)
• Upper airway (throat tightness, dysphagia, dysphonia, hoarseness, stridor)
• Lower airway (wheeze, cough, dyspnea, chest tightness)
• Cardiovascular system (tachycardia, hypotension, pallor, cyanosis, dysrhythmia)
• Skin (urticaria, angioedema, flushing, pruritus—but remember absence doesn't exclude diagnosis)
• Gastrointestinal system (cramping, nausea, vomiting, diarrhea)

Critical Management Principle

Clinical judgment overrides formal diagnostic criteria—epinephrine should be administered when anaphylaxis is suspected, even if the patient does not yet meet all formal criteria. 1, 2 Do not delay treatment waiting for additional symptoms to develop, as anaphylaxis exists on a continuum and can progress rapidly from mild to life-threatening. 2

Laboratory Testing Limitations

The diagnosis of anaphylaxis is clinical and must be made rapidly without waiting for laboratory confirmation. 3, 2 While serum tryptase levels (drawn 1-2 hours after symptom onset) can retrospectively confirm mast cell activation, they have minimal utility in acute diagnosis and should never delay treatment. 3