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History
Presenting pattern
Symptom characterization
Wheals
Transient lesions
Migratory lesions
Angioedema
Lips
Tongue
Periorbital
Duration classification
Acute urticaria less than 6 weeks (L50.9)
Chronic urticaria 6 weeks or longer (L50.8)
Episode pattern
Continuous daily or near daily
Intermittent episodic
OPQRST
OPQRST framework
Use for time course and triggers
Use for severity and systemic involvement
Onset
Onset details
Time of first lesion
Time from exposure to rash
First ever episode vs recurrent
Provocation/Palliation
Trigger and relief pattern
Medication exposures
NSAIDs
Antibiotics
ACE inhibitor
Infection context
Viral syndrome
Recent fever illness
Physical triggers
Pressure
Cold
Heat
Exercise
Relief factors
Antihistamine response
Removal from exposure
Quality
Lesion sensation
Pruritus
Burning pain
Painful lesions suggesting vasculitis
Region/Radiation
Distribution
Generalized
Face and mucosa
Acral predominance
Pressure areas
Severity
Severity impact
Sleep disruption
School or work disruption
Severe swelling impairing speech or swallowing
Timing
Timing features
Individual lesion duration less than 24 hours
Individual lesion duration 24 hours or longer suggesting vasculitis
Nocturnal predominance
Associated symptoms
Systemic symptoms screen for anaphylaxis and mimics
Respiratory
Dyspnea
Wheeze
Stridor
Cardiovascular
Syncope
Chest tightness
Palpitations
Gastrointestinal
Repetitive vomiting
Crampy abdominal pain
Diarrhea
Constitutional
Fever
Weight loss
Night sweats
Alarm Features
Immediate life threats
High risk presentations
Anaphylaxis (T78.2)
Hypotension
Respiratory compromise
Upper airway angioedema
Tongue swelling
Voice change
Drooling
Severe asthma exacerbation triggered by allergy
Silent chest
Fatigue or altered mental status
Vital sign danger thresholds
Danger thresholds
Systolic blood pressure less than 90 mmHg or age adjusted low
Oxygen saturation less than 92 percent on room air
Respiratory rate 30 per minute or higher with distress
Altered mental status
High risk exam findings
High risk findings
Stridor
Immediate airway planning
Immediate epinephrine if anaphylaxis suspected
Rapidly progressive facial or tongue edema
Immediate airway planning
Early anesthesia or ENT support
Purpura or bruising with urticarial lesions
Urticarial vasculitis concern
Systemic involvement evaluation
Escalation triggers
Immediate escalation criteria
Worsening swelling over minutes
Recurrent symptoms after initial improvement
Need for repeated epinephrine doses
Poor social support or unreliable return
Medications
Current and recent exposures
Medication and substance review
New prescription medication within 6 weeks
Recent dose increase within 2 weeks
OTC exposures
NSAIDs
Cold and flu preparations
Supplements and herbals
New supplement within 6 weeks
High dose biotin affecting labs
High risk medication classes
Common urticaria and angioedema triggers
NSAIDs
Urticaria exacerbation in chronic spontaneous urticaria
Bronchospasm risk in aspirin sensitive asthma
ACE inhibitor
Bradykinin mediated angioedema risk
Poor response to antihistamines expected
Opioids
Non IgE histamine release
Pruritus and flushing mimic
Contraindications and interaction traps
Therapy safety considerations
Sedating antihistamines
Fall risk in older adults
Driving impairment risk
QT prolongation risk medications
Hydroxyzine higher risk settings
Concomitant QT prolonging agents
Diet
Food and exposure context
Exposure patterns
New food exposure within 4 hours
Known food allergy exposure
Alcohol exposure
Vasodilation and symptom amplification
Co factor for food dependent exercise anaphylaxis
Hydration and intake
Intake context
Poor oral intake
Vomiting limiting oral meds
Dehydration contributing to hypotension concern
Review of Systems
System based screen
ROS clusters
Skin
Urticaria
Bruising or purpura
ENT
Throat tightness
Hoarseness
Pulmonary
Wheeze
Cough
Cardiovascular
Syncope or presyncope
Lightheadedness
Gastrointestinal
Abdominal pain
Vomiting
Musculoskeletal
Arthralgia
Myalgia
Endocrine
Heat intolerance
Cold intolerance
Collateral History and Family History
Source and reliability
Collateral and context
Witnessed exposure history
Timing reliability
Prior allergy testing records
Family history
Inherited and atopic conditions
Hereditary angioedema (D84.1)
Family members with recurrent swelling
Family members with abdominal attacks
Atopy
Asthma (J45.909)
Allergic rhinitis (J30.9)
Autoimmune disease
Autoimmune thyroid disease (E06.3)
Systemic lupus erythematosus (M32.9)
Risk Factors
Patient specific risks
Comorbidity risks
Asthma severity
Higher risk severe anaphylaxis
Lower reserve with bronchospasm
Cardiovascular disease
Higher risk epinephrine adverse effects
Lower tolerance of hypotension
Pregnancy
Airway edema risk
Medication risk benefit considerations
Exposure risks
Exposure and setting
Recent infection exposure
Recent vaccination
Hymenoptera exposure risk
Medication related risks
Bradykinin angioedema risks
ACE inhibitor use
ARB related angioedema history
Differential Diagnosis
Life threatening
Cannot miss diagnoses
Anaphylaxis (T78.2)
Urticaria plus respiratory compromise
Urticaria plus hypotension or syncope
Angioedema with airway compromise
Tongue or laryngeal edema
Rapid progression over minutes
Meningococcemia (A39.0)
Fever with petechiae or purpura
Toxic appearance
Common
Common etiologies
Acute spontaneous urticaria (L50.9)
Often infection associated
Often no trigger identified
Drug associated urticaria (L50.0)
Temporal relationship to new medication
Improvement after discontinuation
Physical inducible urticaria (L50.8)
Dermatographism
Cold urticaria
Less common
Less common etiologies and mimics
Chronic spontaneous urticaria (L50.8)
Daily or near daily wheals for 6 weeks or longer
Autoimmune association
Urticarial vasculitis (L95.8)
Lesions lasting 24 hours or longer
Residual bruising or hyperpigmentation
Serum sickness like reaction (T80.69)
Fever
Arthralgia
Mast cell disorders
Recurrent flushing and syncope
Elevated baseline tryptase
Past Medical History
Relevant conditions
Baseline conditions
Prior anaphylaxis episodes
Trigger known
Epinephrine autoinjector access
Chronic urticaria history
Prior response to antihistamines
Prior need for omalizumab
Angioedema history
ACE inhibitor associated episodes
Family history suggesting hereditary angioedema
Procedures and hospitalizations
Prior care utilization
Prior ED visits for allergic reactions
Prior ICU admission for airway compromise
Physical Exam
General and vitals
Initial assessment
Vital sign pattern
Hypotension
Tachycardia
Appearance
Toxic appearance
Respiratory distress
Skin
Skin findings
Urticarial wheals
Blanching
Raised edematous plaques
Lesion duration clues
Individual lesion less than 24 hours
Fixed lesions 24 hours or longer
Mimic clues
Target lesions suggesting erythema multiforme
Non blanching petechiae or purpura
Airway and ENT
Upper airway evaluation
Lip and tongue swelling
Uvula edema
Voice change
Drooling or inability to handle secretions
Pulmonary
Respiratory findings
Wheeze
Stridor
Increased work of breathing
Cardiovascular and perfusion
Perfusion and shock signs
Capillary refill delay
Cool clammy skin
Altered mentation
GI and other systems
Systemic involvement
Abdominal tenderness
Joint swelling or tenderness
Lab Studies
No routine labs for uncomplicated acute urticaria
Minimal testing strategy
No labs for isolated urticaria with stable vitals
Targeted labs for systemic features or chronic course
Anaphylaxis and severe reaction evaluation
Severe reaction labs
Serum tryptase
Useful if drawn within 1 to 3 hours of symptom onset
Baseline repeat 24 hours later for comparison
Basic metabolic panel
Electrolytes and renal function for shock and fluids
Glucose for altered mental status
Chronic urticaria targeted workup
Chronic course labs
CBC with differential
Eosinophilia suggesting parasitic or drug reaction
Neutrophilia suggesting infection or inflammation
ESR or CRP
Elevated values supporting vasculitis or systemic disease
Normal values supporting uncomplicated chronic spontaneous urticaria
TSH with reflex free T4
Autoimmune thyroid association
Treatment rarely resolves urticaria alone
Liver enzymes
Baseline prior to advanced therapies
Hepatitis association screening context
Angioedema complement evaluation
Bradykinin mediated angioedema labs
C4 level
Low in hereditary angioedema during attacks
Normal level does not exclude ACE inhibitor angioedema
C1 inhibitor antigen and function
Confirm hereditary angioedema types
Specialist interpretation preferred
Imaging
Scoring Systems
Criteria based tools
NIAID FAAN anaphylaxis clinical criteria
Acute illness with skin mucosal involvement plus respiratory compromise
Acute illness with skin mucosal involvement plus reduced blood pressure
WAO anaphylaxis criteria
Acute onset illness with airway breathing circulation compromise
Exposure plus hypotension or bronchospasm even without skin findings
MRI
Rare indications
Alternative diagnosis evaluation when focal neurologic symptoms present
Avoid as routine for urticaria evaluation
CT
Airway and alternative diagnosis imaging
CT neck with contrast local protocol dependent
Consider when deep neck infection is suspected
Consider when airway symptoms with unclear cause
CT chest local protocol dependent
Consider when pulmonary embolism concern dominates
Not for routine urticaria
Ultrasound
Targeted ultrasound use
Soft tissue ultrasound
Abscess vs cellulitis when swelling is focal
Not for diffuse urticaria
Abdominal ultrasound
Consider in recurrent abdominal attacks with hereditary angioedema history
Rule out alternative abdominal pathology
Special Tests
Bedside and procedural diagnostics
Targeted tests by phenotype
Dermatographism provocation
Linear wheal after stroking skin
Supports physical inducible urticaria
Cold stimulation test
Ice cube test positive wheal
Anaphylaxis risk with cold water immersion history
Skin biopsy for suspected urticarial vasculitis
Lesions lasting 24 hours or longer
Purpura or residual hyperpigmentation
Airway evaluation
Airway confirmation tools
Flexible nasolaryngoscopy local protocol dependent
Suspected laryngeal edema
Persistent voice change or stridor
ECG
Indications in urticaria presentations
ECG triggers
Chest pain or palpitations during reaction
Older patient receiving epinephrine
Known cardiovascular disease with anaphylaxis
High risk patterns
ECG red flags
Ischemic ST changes
Ventricular tachyarrhythmia
Prolonged QT interval in high risk medication settings
Assessment
Phenotype and severity stratification
Working problem list
Isolated urticaria without systemic features
Stable vitals
No respiratory or cardiovascular symptoms
Urticaria with angioedema
Mucosal involvement present
Airway risk stratified by symptoms
Anaphylaxis suspected (T78.2)
Skin symptoms plus respiratory compromise
Skin symptoms plus hypotension or syncope
Etiology hypothesis
Likely trigger category
Idiopathic or infection associated
No clear exposure
Viral prodrome present
Medication associated
Temporal relationship to exposure
Reproducible with re exposure history
Physical inducible
Reproducible stimulus
Limited distribution pattern
Plan
First 5 minutes for critical patient
Immediate stabilization workflow
Monitoring
Cardiac monitor
Pulse oximetry
Access
Two IV lines for hypotension or anaphylaxis
Intraosseous access if no IV access in shock
Oxygen
Supplemental oxygen for oxygen saturation less than 92 percent
Early airway planning for stridor or voice change
Epinephrine for anaphylaxis
Adult epinephrine IM 0.3 mg to 0.5 mg of 1 mg per mL into lateral thigh
Repeat every 5 to 15 minutes if persistent symptoms
Pharmacologic ladder for isolated urticaria
Symptom control
Second generation H1 antihistamine first line
Cetirizine 10 mg PO daily
Fexofenadine 180 mg PO daily
Up dosing for persistent symptoms off label
Cetirizine 20 mg PO twice daily maximum 40 mg per day
Fexofenadine 180 mg PO twice daily maximum 360 mg per day
Sedating H1 antihistamine adjunct
Diphenhydramine 25 mg to 50 mg PO or IV every 6 hours as needed
Hydroxyzine 25 mg PO every 6 hours as needed
H2 blocker adjunct
Famotidine 20 mg PO or IV twice daily
Limited incremental benefit over H1 alone
Glucocorticoid short course selected cases
Prednisone 40 mg PO daily for 3 to 5 days
Avoid for uncomplicated mild cases
Anaphylaxis treatment bundle
Time critical therapy
Epinephrine first line
Adult epinephrine IM 0.3 mg to 0.5 mg of 1 mg per mL into lateral thigh
Pediatric epinephrine IM 0.01 mg per kg of 1 mg per mL maximum 0.3 mg
IV fluids for hypotension
Normal saline 1 L bolus adult
Repeat bolus based on perfusion and blood pressure
Bronchospasm
Albuterol nebulized 2.5 mg to 5 mg
Repeat based on response
Adjunct antihistamine
Diphenhydramine 25 mg to 50 mg IV or PO
Not a substitute for epinephrine
Adjunct steroid
Methylprednisolone 125 mg IV selected cases
Does not prevent early airway compromise
Angioedema phenotype specific management
Histaminergic angioedema likely
Similar treatment to urticaria
Epinephrine if anaphylaxis features present
Bradykinin mediated angioedema suspected
ACE inhibitor discontinuation
Avoid future ACE inhibitor exposure
Document as drug reaction
Airway priority
Early anesthesia or ENT support for tongue or laryngeal symptoms
Lower threshold for intubation if progression
Targeted therapies local protocol dependent
C1 inhibitor concentrate 20 units per kg IV for hereditary angioedema
Icatibant 30 mg subcutaneous single dose for hereditary angioedema
Reassessment loop
Response monitoring and repeat exams
Recheck vitals every 15 minutes until stable after epinephrine
Repeat airway exam after each intervention
Symptom recurrence watch for biphasic reaction
Disposition
Level of care criteria
ICU criteria
Persistent hypotension after fluids and repeated epinephrine
Need for epinephrine infusion local protocol dependent
Airway intervention or impending airway compromise
Inpatient admission criteria
Progressive angioedema without secured airway
Significant comorbidity with moderate reaction
Unreliable follow up or unsafe home setting
Observation pathway criteria
Anaphylaxis treated with epinephrine
Need for multiple epinephrine doses
Severe asthma history
Discharge criteria
Stable vitals for an appropriate observation period
No progression of angioedema
Patient understands return precautions and has medications
Discharge Instructions
Copy discharge instructions
Discharge text
You were treated for hives with or without swelling
Take your antihistamine as directed for the next several days
Avoid any suspected trigger and avoid NSAIDs if they worsened symptoms
If you were given an epinephrine autoinjector carry it with you at all times
Use epinephrine right away if you develop trouble breathing, throat tightness, fainting, or repeated vomiting
Return to the emergency department now for trouble breathing, voice change, swelling of tongue, fainting, chest pain, or symptoms coming back after improvement
Follow up with your primary care clinician within 2 to 3 days
Allergy specialist referral within 2 to 6 weeks for recurrent episodes or unclear triggers
References
Guidelines and key sources
Evidence based sources
EAACI GA2LEN EDF WAO guideline for urticaria 2021 update
AAAAI ACAAI practice parameter update for the diagnosis and management of acute and chronic urticaria 2014
World Allergy Organization anaphylaxis guidance 2020 update
NIAID FAAN anaphylaxis clinical criteria 2006
ACE inhibitor associated angioedema reviews and society guidance local protocol dependent
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.