What are the diagnostic criteria for anaphylaxis?

Diagnostic Criteria for Anaphylaxis

Anaphylaxis is diagnosed when any one of three specific clinical criteria is fulfilled, as established by the National Institute of Allergy and Infectious Diseases and Food Allergy and Anaphylaxis Network (NIAID/FAAN) guidelines. 1

The Three Diagnostic Criteria

Anaphylaxis is highly likely when any ONE of the following three criteria is met:

Criterion 1

Acute onset of illness (minutes to several hours) involving skin/mucosal tissue (e.g., generalized hives, pruritus, flushing, swollen lips-tongue-uvula) AND at least ONE of the following:

• Respiratory compromise (e.g., dyspnea, wheeze, bronchospasm, stridor, hypoxemia)
• Reduced blood pressure or associated symptoms of end-organ dysfunction (e.g., hypotonia, syncope, incontinence)

Criterion 2

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

• Involvement of skin/mucosal tissue (e.g., generalized hives, itch-flush, swollen lips-tongue-uvula)
• Respiratory compromise (e.g., dyspnea, wheeze, cough, stridor, hypoxemia)
• Reduced blood pressure or associated symptoms (e.g., hypotonia, syncope, incontinence)
• Persistent gastrointestinal symptoms (e.g., crampy abdominal pain, vomiting)

Criterion 3

Reduced blood pressure after exposure to a known allergen (minutes to several hours):

• For adults: systolic BP <90 mmHg or >30% decrease from baseline
• For children: age-specific low systolic BP or >30% decrease from baseline
  • Age 1 month to 1 year: <70 mmHg
  • Age 1-10 years: <(70 mmHg + [2 × age in years])
  • Age 11-17 years: <90 mmHg

Important Clinical Considerations

Presentation Variations

• Cutaneous symptoms (hives, flushing, angioedema) occur in most patients but are absent in 10-20% of cases, including many fatal reactions 1
• Respiratory symptoms occur in up to 70% of cases 1
• Gastrointestinal symptoms occur in up to 40% of cases 1
• Symptoms typically develop rapidly over minutes to several hours 1

Diagnostic Challenges

• Laboratory tests have poor sensitivity in confirming anaphylaxis in the acute setting 1
• Clinical judgment remains essential, as these criteria are helpful but should not replace clinician assessment 1
• Death from anaphylaxis can occur within 30 minutes to 2 hours of exposure 1

Special Populations

• In infants and young children, hypotension may be a late manifestation of hypovolemic shock 1
• Tachycardia, even without hypotension, may indicate shock in pediatric patients 1
• Adolescents and young adults with asthma are at higher risk for severe or fatal anaphylaxis 2

Differential Diagnosis Considerations

Anaphylaxis must be distinguished from:

• Isolated allergen-associated urticaria (which may respond to antihistamines alone) 1
• Vasovagal syncope
• Panic attack
• Other causes of shock

Management Implications

Early recognition using these criteria is critical because:

• Epinephrine is the first-line treatment and should be administered as soon as anaphylaxis is suspected 1, 3
• Delayed administration of epinephrine is associated with poor outcomes including fatality 1
• Antihistamines alone are inadequate for treating anaphylaxis 2

These diagnostic criteria have been prospectively validated in emergency department settings with a positive likelihood ratio of 3.26 and negative likelihood ratio of 0.07, making them reliable tools for identifying anaphylaxis 1.