No routine labs for uncomplicated acute urticaria Level B
Low diagnostic yield in typical cases
Treatment response not lab dependent
Targeted labs for alternate diagnosis concern Level C
Vasculitis suspicion
Bradykinin angioedema suspicion
Targeted labs when indicated
Basic tests for systemic involvement
Complete blood count for infection or hematologic concern
Eosinophilia supportive drug reaction or parasitic risk
Leukocytosis supportive infection
Electrolytes and creatinine for severe vomiting or hypotension
Dehydration markers
Acute kidney injury markers
Anaphylaxis adjuncts
Serum tryptase for severe reactions and diagnostic uncertainty
Peak window within 1 to 3 hours after onset
Normal result does not exclude anaphylaxis
Bradykinin mediated angioedema evaluation
C4 level for hereditary angioedema screening
Low C4 supportive
Normal C4 does not fully exclude
C1 esterase inhibitor quantity and function for confirmation
Low function supportive
Specialist follow up typical
Diagnostic Tests
Scoring Systems
Criteria frameworks
NIAID FAAN anaphylaxis criteria
High sensitivity reported in ED validation studies
Practical bedside trigger for epinephrine Class I
WAO anaphylaxis criteria
Similar to NIAID criteria
Emphasis on rapid recognition
Symptom activity tools
Urticaria Activity Score UAS7 for recurrent patterns
Daily hive count and itch severity tracking
Specialist follow up utility
Angioedema activity or severity tracking tools
Symptom diary framework
Trigger correlation aid
MRI
MRI role
Not indicated for routine urticaria Level C
No diagnostic benefit for typical transient wheals
Avoid delays in time sensitive anaphylaxis care
Rare indications for alternative diagnosis
CNS symptoms suggesting other pathology
Soft tissue evaluation when abscess mimic and CT avoided
CT
CT role
Not indicated for isolated urticaria Level C
Clinical diagnosis
Low yield
Indications for airway concern escalation
Deep neck infection concern
Severe facial swelling with uncertain source
Ultrasound (or US)
Ultrasound role
Not required for typical urticaria Level C
Lesions superficial and clinical
Management unchanged
POCUS adjuncts for unstable presentations
IVC and cardiac views for shock phenotype
Lung ultrasound for alternative dyspnea causes
Disposition
Observation and admission criteria
Disposition stratification
Discharge criteria
Isolated urticaria
No respiratory or cardiovascular symptoms
Observation criteria
Angioedema involving lips or face
Recent epinephrine administration
Admission criteria
Airway involvement
Recurrent symptoms during observation
Observation timing principles
Anaphylaxis risk based observation after epinephrine
Longer observation if severe reaction or multiple epinephrine doses
Shorter observation may be appropriate if rapid full resolution and low risk
Follow up planning
Outpatient follow up
Primary care follow up within 2 to 7 days for persistent symptoms
Trigger review
Medication tolerance
Allergy referral indications
Suspected food or drug allergy
Recurrent episodes or angioedema without hives
Medication safety planning
Driving and sedation counseling for first generation antihistamines
Avoid machinery use
School or work safety discussion
Treatment
First line symptom control
H1 antihistamines Class I
Second generation preferred
Lower sedation
Longer duration
Up dosing to as high as 4 times standard dose for refractory symptoms Level B
Adult options
Cetirizine oral
Standard 10 mg daily
If refractory, increase to 20 mg daily
If severe, increase to 40 mg daily in divided doses
Loratadine oral
Standard 10 mg daily
If refractory, increase to 20 mg daily
If severe, increase to 40 mg daily in divided doses
Fexofenadine oral
Standard 180 mg daily
If refractory, increase to 180 mg twice daily
If severe, increase to 360 mg twice daily
Pediatric options
Cetirizine oral
Age 2 to 5 years 2.5 to 5 mg daily
Age 6 years and older 10 mg daily
Specialist guided up dosing for refractory symptoms
Loratadine oral
Age 2 to 5 years 5 mg daily
Age 6 years and older 10 mg daily
First generation H1 antihistamines Level C
Breakthrough nocturnal pruritus use
Sedation risk
Anticholinergic effects risk
Adult options
Diphenhydramine oral or IV
25 to 50 mg every 6 hours as needed
Avoid in high fall risk
Hydroxyzine oral
25 mg every 6 to 8 hours as needed
QT prolongation risk consideration
Adjunct medications
H2 antihistamines Level C
Add on for persistent hives despite H1 therapy
Modest incremental benefit for cutaneous symptoms
Not a substitute for epinephrine in anaphylaxis
Adult options
Famotidine oral or IV
20 mg twice daily
Renal dosing adjustment
Pediatric options
Famotidine
0.5 mg per kg per dose twice daily
Maximum 20 mg per dose
Systemic corticosteroids Level C
Indications
Severe widespread urticaria not controlled with antihistamines
Significant angioedema without airway compromise
Risks
Hyperglycemia
Mood changes
Adult options
Prednisone oral
40 to 60 mg daily for 3 to 5 days
No taper needed for short course
Pediatric options
Prednisone oral
1 mg per kg daily for 3 to 5 days
Maximum 50 mg daily
Anaphylaxis pathway when criteria met
Epinephrine IM Class I
Dosing
0.01 mg per kg of 1 mg per ml solution IM
Maximum 0.5 mg per dose
Administration site
Anterolateral thigh preferred
Repeat every 5 to 15 minutes if persistent symptoms
Adjuncts after epinephrine
Isotonic crystalloid bolus for hypotension
Inhaled beta agonist for bronchospasm
Refractory anaphylaxis escalation Class IIa
Epinephrine infusion for persistent shock after IM dosing
Initiate in monitored setting
Titrate to blood pressure and perfusion targets
Glucagon for beta blocker associated refractory response
Nausea and vomiting risk
Continuous monitoring requirement
Trigger avoidance and supportive care
Avoidance advice Level B
NSAID avoidance during active episode
Exacerbation risk
Alternative analgesics
Alcohol avoidance during active episode
Vasodilation worsens pruritus risk
Sleep disruption risk
Skin care measures Level C
Cool compresses
Itch relief
Avoid overheating
Fragrance free emollients
Barrier support
Irritant reduction
Special Populations
Pregnancy
Pregnancy considerations
Maternal stabilization priority Class I
Epinephrine for anaphylaxis not withheld
Left lateral positioning for hypotension symptoms
Antihistamine selection
Cetirizine acceptable option
Loratadine acceptable option
Corticosteroids
Short course if severe symptoms
Hyperglycemia monitoring if gestational diabetes
Geriatric
Older adult considerations
Sedation vulnerability
Avoid first generation antihistamines when possible
Fall risk mitigation
Anticholinergic burden
Urinary retention risk
Delirium risk
Cardiovascular comorbidity
Monitoring after epinephrine if anaphylaxis
Medication interaction review
Pediatrics
Pediatric considerations
Anaphylaxis recognition without hypotension
Respiratory compromise and skin findings common
Early epinephrine threshold
Weight based dosing accuracy
Current weight use
Maximum dose limits
Discharge planning
Caregiver education on recurrence
Return precautions clearly listed
Background
Epidemiology
Epidemiology overview
Acute urticaria common ED presentation
Many cases idiopathic
Infection and medication triggers frequent
Course
Most episodes resolve within days to weeks
Progression to chronic urticaria uncommon
Anaphylaxis association
Urticaria may be first visible sign
Systemic symptoms define severity risk
Pathophysiology
Mechanisms
Mast cell activation
Histamine release drives wheal and flare
Pruritus mediated by histamine and neuropeptides
IgE mediated pathway subset
Rapid onset after exposure
Higher recurrence with re exposure
Non IgE mediated pathways
NSAID related pseudoallergy
Infection related immune activation
Bradykinin mediated angioedema
No urticaria typical
Poor response to antihistamines and steroids
Therapeutic Considerations
Treatment rationale
H1 blockade first line
Reduces itch and wheal formation
Second generation preferred for safety
Up dosing strategy
Dose response relationship for refractory symptoms
Monitor sedation and anticholinergic effects
Steroid role limited
Short courses for severe refractory symptoms
Avoid routine use in mild cases
Epinephrine for anaphylaxis
Alpha effects improve vascular tone
Beta effects improve bronchospasm and mediator release
Patient Discharge Instructions
copy discharge instructions
Discharge instructions
Diagnosis explanation
Hives and itching from temporary skin swelling
Often no single clear trigger found
Medications
Daily non drowsy antihistamine as directed
Avoid extra sedating antihistamines unless advised
Avoidance
Avoid NSAIDs during active hives
Avoid alcohol until symptoms gone
Skin comfort
Cool showers
Cool compresses
Return to emergency immediately for red flags
Trouble breathing
Wheeze
Throat tightness
Voice change
Swelling of tongue or lips that is worsening
Dizziness or fainting
Repeated vomiting
Follow up
Primary care within 2 to 7 days if not improving
Allergy referral if repeated episodes or suspected specific trigger
References
Guidelines and key sources
Evidence sources
American Academy of Emergency Medicine guideline on acute urticaria and angioedema
ED evaluation and management focus
Limited role for routine laboratory testing
International urticaria guideline EAACI GA2LEN EuroGuiDerm APAAACI 2021 update
Second generation H1 antihistamine first line
Up dosing up to fourfold for refractory symptoms
Primary care review sources
Acute urticaria first line second generation H1 antihistamines
Up dosing strategy cautions
Anaphylaxis criteria and emergency care sources
NIAID FAAN anaphylaxis criteria
High sensitivity in ED validation studies
Bedside recognition framework
Pediatric anaphylaxis emergency treatment position statements
Epinephrine first line
Antihistamines and steroids second line
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.