Overview
Acute Urticaria
Quick Reference
Critical Alerts
- Rule out anaphylaxis: Urticaria + respiratory/cardiovascular symptoms = anaphylaxis
- Angioedema involving airway is life-threatening: Lips, tongue, throat swelling
- ACE inhibitor angioedema does NOT respond to antihistamines or epinephrine: Stop ACE-I; may need airway intervention
- Antihistamines are first-line treatment: H1 blockers are mainstay
- Epinephrine for anaphylaxis: Not for uncomplicated urticaria
- Identify and avoid triggers: Prevents recurrence
Anaphylaxis vs Uncomplicated Urticaria
| Feature | Urticaria | Anaphylaxis |
|---|---|---|
| Skin | Hives only | Hives + other symptoms |
| Respiratory | None | Stridor, wheeze, dyspnea |
| Cardiovascular | Normal BP | Hypotension, syncope |
| GI | None | Nausea, vomiting, cramping |
| Treatment | Antihistamines | Epinephrine IM |
Emergency Treatments
| Condition | Treatment |
|---|---|
| Uncomplicated urticaria | H1 antihistamine (cetirizine 10mg or diphenhydramine 25-50mg) |
| Moderate/Severe urticaria | H1 + H2 blocker (famotidine) ± steroids |
| Urticaria + anaphylaxis | Epinephrine 0.3-0.5mg IM + antihistamines + steroids |
| ACE-I angioedema (airway) | Stop ACE-I, airway management, ± icatibant or FFP |
Definition
Overview
Urticaria (hives) is characterized by pruritic, erythematous, raised wheals caused by mast cell degranulation and histamine release. It is classified as acute (<6 weeks) or chronic (≥6 weeks). Most acute cases are self-limited and respond to antihistamines. The key ED task is distinguishing uncomplicated urticaria from anaphylaxis and managing angioedema appropriately.
Classification
By Duration:
| Type | Duration |
|---|---|
| Acute | <6 weeks |
| Chronic | ≥6 weeks |
By Mechanism:
| Type | Mechanism | Examples |
|---|---|---|
| IgE-mediated | Type I hypersensitivity | Food, drug, insect sting allergy |
| Non-IgE-mediated | Direct mast cell activation | Opioids, contrast, cold, pressure |
| Autoimmune | Autoantibodies against IgE/FcεRI | Chronic spontaneous urticaria |
Epidemiology
- Lifetime prevalence: 15-25%
- Acute urticaria more common: Than chronic
- Cause identified in ~50%: Often unknown
- Most resolve spontaneously: Within hours to days
Etiology
Common Triggers:
| Category | Examples |
|---|---|
| Foods | Shellfish, nuts, eggs, milk |
| Drugs | Antibiotics (penicillins, sulfa), NSAIDs, opioids |
| Insect stings | Bees, wasps |
| Infections | Viral (URI), bacterial |
| Physical | Cold, heat, pressure, vibration, exercise |
| Idiopathic | No identifiable cause (majority) |
Pathophysiology
Mechanism
- Mast cell activation: IgE-mediated or direct activation
- Degranulation: Release of histamine, leukotrienes, prostaglandins
- Vascular effects: Vasodilation, increased permeability
- Wheal formation: Localized edema in dermis
- Angioedema: Deeper edema in dermis/subcutis
Angioedema
- Deeper swelling (dermis and subcutaneous tissue)
- Commonly affects face, lips, tongue, extremities, genitals
- Can involve airway → Life-threatening
- May occur with or without urticaria
ACE Inhibitor Angioedema
- Bradykinin-mediated (not histamine)
- Occurs in 0.1-0.7% of ACE-I users
- Often delayed onset (weeks to years after starting)
- Does NOT respond to antihistamines, steroids, or epinephrine
- Requires stopping ACE-I; may need icatibant or FFP
Clinical Presentation
Symptoms
| Finding | Description |
|---|---|
| Pruritic wheals | Raised, erythematous, blanching |
| Migratory | Lesions come and go |
| Individual lesion duration | <24 hours (usually minutes to hours) |
| No scarring | Resolves completely |
| Angioedema | Lip, face, tongue swelling; may affect extremities |
History
Key Questions:
Physical Examination
Skin:
| Finding | Significance |
|---|---|
| Erythematous, raised wheals | Urticaria |
| Central pallor | Classic "hive" appearance |
| Dermographism | Wheal formation with stroking skin |
| Facial/lip swelling | Angioedema |
| Tongue swelling | Airway risk |
Systemic Assessment (Rule Out Anaphylaxis):
| Finding | Concern |
|---|---|
| Stridor, wheezing | Airway compromise |
| Hypotension | Distributive shock |
| Tachycardia | Anaphylaxis |
| Abdominal cramping, vomiting | GI involvement |
When did it start? How long have individual lesions been present?
Common presentation.
New medications (especially last 2-4 weeks)?
Common presentation.
New foods?
Common presentation.
Insect stings or bites?
Common presentation.
History of prior allergic reactions?
Common presentation.
ACE inhibitor or NSAID use?
Common presentation.
Any difficulty breathing, swallowing, dizziness?
Common presentation.
Recent infections (viral, bacterial)?
Common presentation.
Prior episodes?
Common presentation.
Red Flags
Signs of Anaphylaxis
| Finding | Action |
|---|---|
| Stridor or voice change | Epinephrine IM, airway management |
| Wheezing/Dyspnea | Epinephrine IM |
| Hypotension | Epinephrine IM, IV fluids |
| Syncope | Epinephrine IM, IV fluids |
| Nausea, vomiting, cramping (with urticaria) | Consider anaphylaxis |
Airway-Threatening Angioedema
| Finding | Action |
|---|---|
| Tongue swelling | Prepare for intubation |
| Uvula edema | Prepare for intubation |
| Difficulty swallowing or speaking | Immediate airway evaluation |
| ACE-I angioedema | Stop drug; icatibant or FFP; surgical airway may be needed |
Differential Diagnosis
Other Causes of Pruritic Rash
| Diagnosis | Features |
|---|---|
| Anaphylaxis | Urticaria + respiratory/CV symptoms |
| Contact dermatitis | Localized, vesicular, pruritic |
| Erythema multiforme | Target lesions, often with mucous membrane involvement |
| Drug eruption | Fixed drug eruption, morbilliform rash |
| Vasculitis (urticarial vasculitis) | Lesions persist >4h, may be painful, petechiae |
| Insect bites | Papular, may be grouped |
| Mastocytosis | Chronic/recurrent, systemic symptoms |
Diagnostic Approach
Clinical Diagnosis
- Urticaria is a clinical diagnosis
- Labs rarely needed for acute uncomplicated cases
When to Consider Testing
| Test | Indication |
|---|---|
| CBC | Infection, eosinophilia |
| Tryptase | If anaphylaxis suspected (elevated acutely) |
| Skin prick/Specific IgE | Outpatient; identify specific allergen |
| C4 level | Hereditary angioedema (low C4) |
| ESR/CRP | If urticarial vasculitis suspected |
Imaging
- Not typically indicated
- Consider if airway involvement (neck soft tissue if time allows)
Treatment
Principles
- Rule out anaphylaxis: Treat immediately if present
- H1 antihistamines are mainstay: First-line
- Identify and avoid triggers if possible
- Steroids for severe/refractory cases
- Airway management for angioedema with tongue/laryngeal involvement
Uncomplicated Urticaria
First-Line: H1 Antihistamine:
| Agent | Dose | Notes |
|---|---|---|
| Cetirizine | 10 mg PO | Non-sedating, fast-acting |
| Loratadine | 10 mg PO | Non-sedating |
| Fexofenadine | 180 mg PO | Non-sedating |
| Diphenhydramine | 25-50 mg PO/IV | Sedating; good for acute |
Second-Line: Add H2 Blocker:
| Agent | Dose |
|---|---|
| Famotidine | 20 mg PO/IV |
| Ranitidine | (Discontinued in many countries) |
Third-Line: Corticosteroids (Severe/Refractory):
| Agent | Dose |
|---|---|
| Prednisone | 40-60 mg PO × 3-5 days |
| Methylprednisolone | 125 mg IV (if unable to take PO) |
Angioedema (Without Anaphylaxis)
Non-ACE-I Angioedema:
- H1 antihistamine
- ± H2 blocker
- ± Steroids
- Monitor airway closely
ACE-Inhibitor Angioedema:
| Intervention | Details |
|---|---|
| Stop ACE inhibitor | Do NOT restart |
| Antihistamines/steroids | NOT effective (bradykinin-mediated) |
| Icatibant | 30 mg SC (bradykinin B2 receptor antagonist) |
| C1 esterase inhibitor concentrate | Alternative |
| FFP | Contains ACE; may help in emergency |
| Airway management | May need intubation or surgical airway |
Anaphylaxis (Urticaria + Systemic Symptoms)
| Intervention | Details |
|---|---|
| Epinephrine IM | 0.3-0.5 mg (1:1,000) mid-lateral thigh |
| IV fluids | Crystalloids for hypotension |
| H1 antihistamine | Diphenhydramine 25-50 mg IV |
| H2 blocker | Famotidine 20 mg IV |
| Steroids | Methylprednisolone 125 mg IV |
| Repeat epinephrine | q5-15 min if symptoms persist |
| Monitor for biphasic reaction | Observe 4-6 hours |
Disposition
Discharge Criteria
- Uncomplicated urticaria resolved/improving with antihistamines
- No angioedema or resolved angioedema (non-airway)
- No systemic symptoms
- Trigger identified and avoidable (if possible)
- Prescription for antihistamines
Admission/Observation Criteria
- Anaphylaxis (observe 4-6 hours minimum)
- Airway-threatening angioedema
- Severe symptoms not responding to treatment
- ACE-I angioedema requiring monitoring
Referral
| Indication | Referral |
|---|---|
| Recurrent urticaria | Allergy/Immunology |
| Anaphylaxis | Allergy for testing and epi-pen |
| Suspected chronic urticaria | Allergy/Dermatology |
| Hereditary angioedema | Allergy/Immunology |
Patient Education
Condition Explanation
- "You have hives, which is an allergic-type reaction in your skin."
- "It's usually not dangerous unless you have trouble breathing or swallowing."
- "Antihistamines usually control the symptoms."
Home Care
- Take antihistamines as directed (may take regularly for a few days)
- Avoid known triggers (if identified)
- Return if symptoms return or worsen
When to Return / Call 911
- Difficulty breathing or swallowing
- Voice changes or throat tightness
- Dizziness or fainting
- Swelling of lips, tongue, or throat
Epi-Pen (If Anaphylaxis History)
- Prescribe epinephrine auto-injector
- Teach proper use
- Carry at all times
- Allergy referral for testing
Special Populations
Pregnancy
- Urticaria can occur during pregnancy
- Antihistamines generally safe (cetirizine, loratadine preferred)
- Avoid first-generation antihistamines if possible (sedation)
- Epinephrine is safe if anaphylaxis
Children
- Same principles as adults
- Weight-based dosing for antihistamines
- Consider viral etiology (commonly triggers acute urticaria)
Elderly
- Avoid sedating antihistamines (fall risk)
- Cetirizine, loratadine, fexofenadine preferred
- Be aware of polypharmacy
Quality Metrics
Performance Indicators
| Metric | Target | Rationale |
|---|---|---|
| Anaphylaxis identified | 100% | Life-threatening |
| Antihistamine given for urticaria | 100% | First-line treatment |
| Epinephrine for anaphylaxis | 100% | Life-saving |
| Trigger counseling documented | >0% | Prevention |
Documentation Requirements
- Description of lesions (wheals, duration)
- Presence or absence of angioedema
- Systemic symptoms (respiratory, CV, GI)
- Suspected trigger
- Treatment given and response
- Follow-up plan
Key Clinical Pearls
Diagnostic Pearls
- Individual lesions <24 hours = Urticaria: >24 hours → Consider vasculitis
- Urticaria + respiratory/CV = Anaphylaxis: Not just urticaria
- ACE-I angioedema is bradykinin-mediated: Antihistamines/steroids won't work
- Check ACE-I history in any angioedema: Common and dangerous
- Most acute urticaria is idiopathic: Trigger not always found
- Dermographism confirms urticaria: Scratch and watch for wheal
Treatment Pearls
- Antihistamines are first-line: H1 blockers; add H2 if severe
- Non-sedating antihistamines preferred: Cetirizine, loratadine
- Steroids for refractory cases: Short course (3-5 days)
- Epinephrine for anaphylaxis only: Not for uncomplicated urticaria
- Stop ACE-I permanently: Angioedema can recur and worsen
- Observe 4-6 hours post-anaphylaxis: Biphasic reactions occur
Disposition Pearls
- Most urticaria can be discharged: With antihistamines
- Anaphylaxis needs observation: 4-6 hours minimum
- ACE-I angioedema may need admission: Airway monitoring
- Prescribe epi-pen after anaphylaxis: And refer to allergy
- Allergy referral for recurrent cases: Identify trigger
References
- Zuberbier T, et al. The EAACI/GA²LEN/EDF/WAO guideline for the definition, classification, diagnosis and management of urticaria. Allergy. 2018;73(7):1393-1414.
- Bernstein JA, et al. The diagnosis and management of acute and chronic urticaria: 2014 update. J Allergy Clin Immunol. 2014;133(5):1270-1277.
- Zuraw BL. Hereditary angioedema. N Engl J Med. 2008;359(10):1027-1036.
- Bas M, et al. A randomized trial of icatibant in ACE-inhibitor-induced angioedema. N Engl J Med. 2015;372(5):418-425.
- ACEP. Clinical policy: Critical issues in the evaluation and management of adult patients in the emergency department with acute urticaria and angioedema. Ann Emerg Med. 2013;61(5):565-575.
- Sampson HA, et al. Symposium on the definition and management of anaphylaxis. J Allergy Clin Immunol. 2005;115(3):S579-S583.
- Grattan CEH, et al. Management of chronic urticaria. BMJ. 2005;330(7499):1006-1010.
- UpToDate. Acute urticaria and angioedema: Clinical features and diagnosis. 2024.