What are the clinical criteria for diagnosing anaphylaxis?

Clinical Criteria for Diagnosing Anaphylaxis

Anaphylaxis is diagnosed when any one of three NIAID/FAAN clinical criteria is fulfilled, and this diagnosis must be made rapidly based on clinical presentation without waiting for laboratory confirmation. 1, 2

The Three Diagnostic Criteria

The NIAID/FAAN criteria, endorsed by the American Academy of Allergy, Asthma & Immunology, American College of Allergy, Asthma, and Immunology, and the World Allergy Organization, define anaphylaxis when any ONE of the following is present: 1, 2

Criterion 1: Acute Skin/Mucosal Involvement Plus Systemic Compromise

• Sudden onset (minutes to hours) of skin or mucosal symptoms (generalized hives, itching, flushing, swollen lips-tongue-uvula) 1
• PLUS at least one of the following:
  • Respiratory compromise (shortness of breath, wheeze, cough, stridor, hypoxemia) 1
  • Reduced blood pressure OR end-organ dysfunction (hypotonia/collapse, incontinence) 1, 3

Criterion 2: Multi-System Involvement After Allergen Exposure

• Two or more of the following occurring suddenly after exposure to a likely allergen: 1, 2
  • Skin/mucosal symptoms (generalized hives, itch-flush, swollen lips-tongue-uvula) 1
  • Respiratory symptoms (shortness of breath, wheeze, cough, stridor, hypoxemia) 1
  • Reduced blood pressure or end-organ dysfunction (hypotonia/collapse, incontinence) 1
  • Persistent gastrointestinal symptoms (crampy abdominal pain, vomiting) 1, 2

Criterion 3: Isolated Hypotension After Known Allergen

• Reduced blood pressure alone after exposure to a known allergen for that specific patient: 1, 2
  • Adults: Systolic BP <90 mmHg OR >30% decrease from baseline 1
  • Infants (1 month-1 year): Systolic BP <70 mmHg 1
  • Children (1-10 years): Systolic BP <[70 mmHg + (2 × age in years)] 1
  • Children >10 years: Systolic BP <90 mmHg 1

Critical Clinical Pearls

Skin Findings Are NOT Required

• Skin manifestations are absent in 10-20% of anaphylaxis cases, so diagnosis and treatment must not be delayed waiting for cutaneous signs. 3, 4, 5
• Anaphylaxis can present with isolated hypotension after insect stings or isolated respiratory symptoms without any skin involvement. 1

Clinical Judgment Supersedes Formal Criteria

• Epinephrine administration is not limited to patients meeting the formal NIAID/FAAN criteria. 1, 2, 6
• If impending anaphylaxis is suspected (e.g., generalized urticaria immediately after allergen immunotherapy injection), epinephrine should be given even before full criteria are met. 1, 6
• However, isolated allergen-associated urticaria that responds to antihistamines should be distinguished from true anaphylaxis requiring immediate epinephrine. 1, 2

Validation and Performance

• These criteria were prospectively validated in emergency department settings with a positive likelihood ratio of 3.26 and negative likelihood ratio of 0.07, supporting their clinical utility. 1, 2

Timing and Progression

• Symptoms typically begin within minutes to several hours of allergen exposure. 1, 6
• The more rapidly symptoms develop, the more likely the reaction is severe and life-threatening. 6
• Median time to cardiac or respiratory arrest: 5 minutes for iatrogenic reactions, 15 minutes for envenomations, 30 minutes for foods. 4

Essential Clinical Assessment Components

When evaluating for anaphylaxis, systematically assess: 6

• Level of consciousness 6
• Upper and lower airways 6
• Cardiovascular system (blood pressure, heart rate) 6
• Skin and mucosal surfaces 6
• Gastrointestinal system 6
• Additional symptoms: lightheadedness, headache, uterine cramps 6

Key Differential Diagnosis

Vasovagal reaction is the most common mimic of anaphylaxis, distinguished by: 6

• Absence of urticaria 6
• Bradycardia (not tachycardia) 6
• Normal or increased blood pressure 6

Other conditions to exclude: acute anxiety, myocardial dysfunction, pulmonary embolism, systemic mast cell disorders, foreign-body aspiration, acute poisoning, hypoglycemia, seizure disorder. 6