Allergic edema: causes and first aid

Allergic (histamine) angioedema is a rapid, usually itchy swelling of the lips, eyelids, tongue, throat, and sometimes the hands and feet. It often accompanies urticaria and responds well to antiallergic therapy, but requires immediate adrenaline if signs of anaphylaxis occur. This is one clinical reality. Another is bradykinin angioedema: attacks without itching and without urticaria, develop more slowly, last longer, and are of little help with antihistamines and glucocorticosteroids. The main causes are hereditary deficiency or dysfunction of the C1 inhibitor, angiotensin-converting enzyme inhibitors, and, less commonly, other medications or acquired C1 inhibitor deficiency due to oncohematological diseases. [1]

Why is this important? Because there is no "one-size-fits-all" treatment for all types of angioedema. If anaphylaxis is suspected, the first aid is intramuscular adrenaline in the thigh, without waiting for "perfect" criteria; delays increase the risk of severe outcomes. However, for bradykinin-related edema, other medications (icatibant, C1 inhibitor concentrate, etc.) are effective, while antihistamines are virtually ineffective. [2]

What is angioedema in simple terms?

Angioedema is a loose, watery swelling of the deep layers of the skin and mucous membranes. In the histamine-mediated form, immune system cells release histamine, causing blood vessels to become leakier, and fluid to leak into the tissues. In the bradykinin-mediated form, the kinin cascade (bradykinin) is to blame—it also dramatically increases vascular permeability, but through different pathways; this prevents traditional antiallergic medications from working. [3]

Clinical warning signs: itching and urticaria—usually an allergy; the absence of itching and urticaria, a slow onset, and a duration of 24-72 hours—are more in favor of bradykinin. Swelling of the tongue and larynx is always a threat to breathing, regardless of the mechanism. [4]

Table 1. How to distinguish between histamine and bradykinin angioedema

Sign	Histamine (allergic)	Bradykinin
Itching/hives	Often there is	Usually no
Rate of increase	Minutes-hours	Watch
Duration without treatment	12-24 hours	24-72 hours
Response to antihistamines/steroids/epinephrine	Good	Minimal/none
Frequent triggers	Food, medicine, bites, latex	Angiotensin-converting enzyme inhibitors, hereditary forms, C1-inhibitor deficiency

Epidemiology: the scale of the problem

• In the United States, >1,000,000 emergency department visits per year are associated with urticaria/angioedema; approximately 100,000 are coded as angioedema. This highlights the prevalence of "histamine" scenarios. [5]
• Hereditary angioedema (HAo) is a rare disorder with an estimated prevalence of about 1 in 50,000 (range 1:50,000–1:100,000). Acquired C1 inhibitor deficiency is even rarer (1:100,000–1:500,000). [6]
• Angioedema due to angiotensin-converting enzyme inhibitors: risk 0.1-0.7% in those receiving the drug; higher in people of African descent. The risk persists throughout treatment. [7]

Table 2. Numbers that help you navigate

Situation	Grade
Urticaria/Angioedema Visits (USA)	>1,000,000 per year
Hereditary angioedema (type I/II)	≈ 1:50,000
Acquired C1 inhibitor deficiency	≈ 1:100,000-1:500,000
Risk of angioedema with ACE inhibitors	≈ 0.1-0.7% (higher in black patients)

Causes and risk factors

• Allergic (histamine) reactions. Food, drugs, insect bites, latex; in case of systemic manifestations - anaphylaxis. [8]
• Drug-induced bradykinin edema. Angiotensin-converting enzyme inhibitors are the main culprit; less commonly, sacubitril/valsartan and dipeptidyl peptidase-4 inhibitors. The risk is increased in the elderly, in those with a history of drug-induced rashes, and in people of African descent. [9]
• Hereditary forms. Deficiency (type I) or dysfunction (type II) of C1 inhibitor (SERPING1 mutations); less common are forms with normal C1 inhibitor (F12, PLG mutations, etc.). [10]
• Acquired C1 inhibitor deficiency. Associated with lymphoproliferative/autoimmune processes; often with low C1q. [11]

Table 3. Triggers by mechanism

Mechanism	Typical triggers
Histamine	Food, medicine, stings, latex
Bradykinin (medicinal)	ACE inhibitors, less commonly sacubitril/valsartan, DPP-4 inhibitors
Bradykinin (hereditary/acquired)	Trauma, dental procedures, infections, stress, estrogen

Pathogenesis

In histamine-induced angioedema, IgE-mediated activation of mast cells leads to the release of histamine and inflammatory mediators, causing blood vessels to dilate and become permeable. This is why antihistamines, glucocorticosteroids, and adrenaline (in anaphylaxis mode) are effective. [12]

In bradykinin angioedema, hyperactivation of the kallikrein-kinin system (due to C1 inhibitor deficiency/dysfunction, drug effects, or mutations) increases bradykinin levels, which "pushes apart" endothelial cells. Antihistamines and steroids are largely ineffective here, so targeted agents are needed: icatibant, C1 inhibitor concentrate, kallikrein inhibitors, and new prophylactic drugs. [13]

Symptoms and red flags

• Swelling of the face/lips/eyelids/tongue, feeling of distension, sometimes abdominal pain (visceral edema), diarrhea, vomiting.
• With the histamine variant there is often itching and hives; with the bradykinin variant there is none, but the swelling lasts longer and is denser.
• Red flags: hoarseness, lump in throat, difficulty breathing, wheezing, drooling, difficulty speaking - treat as if airway obstruction is imminent.[14]

Table 4. Symptom - what to do

Symptom	Probable mechanism	First tactic
Itching, hives + swelling	Histamine	Adrenaline for systemic symptoms, antihistamines, intravenous corticosteroids as indicated
Slow, firm swelling without itching	Bradykinin	Airway assessment; specific treatment (icatibant, C1 inhibitor)
Abdominal pain, vomiting, diarrhea	Visceral edema (usually HAo)	Hemodynamic monitoring, targeted therapy for HAo
Hoarseness, stridor, salivation	Risk of asphyxia	Call for resuscitation, administer adrenaline if in doubt, prepare for early airway protection

Diagnostics

1. Interview and examination. Are there hives and itching? What preceded it (food, medication, sting, new hypertension therapy)? How quickly did it develop and how long did it last? Are you taking an ACE inhibitor? Have any relatives had similar episodes? [15]
2. Emergency measures. If signs of anaphylaxis occur, immediately administer adrenaline intramuscularly into the thigh (0.01 mg/kg, maximum 0.5 mg in adults) and call an ambulance; repeat after 5-10 minutes if symptoms persist. Diagnostic criteria are not required to initiate adrenaline. [16]
3. Baseline tests for recurrent episodes.

• If the edema is without urticaria, measure C4, C1 inhibitor (antigen) level and its function; if an acquired variant is suspected, measure C1q. Best practices also recommend these measurements in children with edema without wheals. [17]
• If anaphylaxis is suspected, serum tryptase (1-3 hours after the onset of symptoms and control after 24-48 hours) helps confirm mast cell activation. [18]

4. Genetics and phenotype clarification. If HAE is confirmed, SERPING1 testing is performed; if C1 inhibitor is normal and clinical features are convincing, panels (F12, PLG, etc.) are used as indicated. [19]

Table 5. Which tests are needed when

Clinical situation	What are we handing over?	For what
Swelling with hives/itching	Tests are usually not needed in acute cases.	Clinical diagnosis; tryptase - in severe reactions
Edema without urticaria (recurrent)	C4, C1 inhibitor (level and function), C1q	Rule out HAo/acquired C1 inhibitor deficiency
Suspicion of anaphylaxis	Serum tryptase (acute + "basic")	Confirm mast cell activation
Confirmed by the National Association of Agricultural Organizations	Genetics (SERPING1, ± F12/PLG, etc.)	Subtype, family counseling

Differential diagnosis

• Cellulitis/erysipeloid: hot, painful, unilateral, persistent infiltration of the skin - this is not angioedema.
• Pseudoallergies/intolerance: local irritants, cold, pressure - non-IgE mechanism, but symptoms are similar.
• Laryngeal edema due to infection/reflux/trauma - always think about the airway.
• Edema from venous/lymphatic insufficiency is chronic, not “paroxysmal”.

The main delimiter is urticaria/itching and response to antihistamines; plus minimal complement complement in the "non-whealing" phenotype. [20]

Table 6. "Similar, but different"

What's at the reception?	More like	Tips
Warm, painful, red infiltration	Cellulite	Fever, inflammatory markers
Builds up in minutes, itching, blisters	Histamine angioedema	Good response to antihistamines
Slow, firm swelling without itching	Bradykinin angioedema	No response to antihistamines/steroids
Chronic swelling of the limb	Lymphedema/venous congestion	Not in attacks, does not disappear within 24 hours

Treatment

If anaphylaxis is suspected, administer immediate intramuscular epinephrine into the thigh, establish access to oxygen/suction, and observe; there are no life-saving contraindications to epinephrine. This rule saves lives. [21]

Histamine-induced angioedema. The current treatment regimen consists of second-generation antihistamines; in severe cases, short-term systemic glucocorticosteroids are added. For chronic spontaneous urticaria with angioedema, omalizumab (anti-IgE) is indicated: it has been shown to reduce swelling and increase "angioedema-free days." [22]

Bradykinin angioedema (hereditary/acquired, without urticaria). Emergency medications:

• Icatibant (bradykinin B2 receptor antagonist).
• C1 inhibitor concentrate (plasma or recombinant).
• Ekalantide (plasma kallikrein inhibitor; not available in all countries).
  These agents should be administered as early as possible after the onset of an attack. [23]

Angioedema with ACE inhibitors. First and foremost, discontinue the drug immediately and permanently. The evidence for icatibant and C1-inhibitor concentrate is conflicting; early assessment and protection of the airway are key. The use of tranexamic acid is being discussed (observational data; possible benefit and a good safety profile). [24]

Prevention for hereditary angioedema. As of 2025, several long-term prevention options are available, and they are chosen individually:

• Lanadelumab (monoclonal antibody to kallikrein; subcutaneously once every 2-4 weeks).
• Berotralstat (oral kallikrein inhibitor; once daily).
• Subcutaneous or intravenous C1 inhibitor for prophylaxis.
• Garadacimab (Andembry) - FDA-approved factor XIIa inhibitor: loading dose, then once monthly.
• Donidalorsen (Dawnzera) is an FDA-approved antisense prekallikrein drug administered subcutaneously every 4-8 weeks.
  For pregnant women and young children, the drug of choice is a plasma C1 inhibitor. Androgens are considered secondary due to their safety profile. [25]

Table 7. Medicines: what, when and why

Task	Preparation	Note
Anaphylaxis/histamine edema	Adrenaline IM, antihistamines, GCS	Adrenaline first, delays are dangerous
HAo/bradykinin attack	Icatibant; C1-inhibitor concentrate; ekalantide	Early introduction improves outcomes
Long-term prevention of HAE	Lanadelumab; Berotralstat; C1-inhibitor (subcutaneous/IV)	Selection by attack frequency and preferences
Newly approved options (2025)	Garadacimab (FXIIa); Donidalorsen (prekallikrein)	FDA approved for ages ≥12 years; every 4-8 weeks (donidalorsen)

Angioedema and the airway. At any sign of obstruction, early "airway first" management is recommended. If the mechanism is in doubt, adrenaline administration is warranted: if it's histamine, it will help; if it's bradykinin, it won't harm, and you'll gain time for specific therapy and airway management. [26]

When to see a doctor immediately

• Hoarseness, difficulty breathing in/out, a lump in the throat, wheezing, increasing swelling of the tongue or lips.
• Abdominal pain with repeated vomiting and severe weakness.
• The first episode of edema while taking an ACE inhibitor - the drug should be discontinued and an alternative should be discussed. [27]

Table 8. Patient Emergency Plan Reminder

Step	What to do
Recognize	Hoarseness, difficulty breathing, increased swelling of the tongue/lips
Act	Adrenaline IM (if systemic symptoms/doubt present), call an ambulance
Don't delay	Repeat adrenaline after 5-10 minutes if symptoms persist
Notify medical professionals	What medications are you taking? Is there an ACE inhibitor?
Documents	Carry an action plan and a list of medications with you

Forecast

With histamine-induced angioedema, the prognosis is favorable if the trigger is eliminated and appropriate therapy is administered; in some patients, episodes are limited to mild manifestations. With bradykinin-induced forms, the prognosis has improved dramatically: the availability of on-demand therapy and new prophylaxis (lanadelumab, berotralstat, garadacimab, donidalorsen) allows most patients to live without frequent attacks. With angioedema treated with ACE inhibitors, relapses usually cease after drug withdrawal, but the risk of recurrent episodes remains for some time. [28]

Frequently asked questions

Is it "just an allergy"?
Not always. If there is itching and hives, an allergy is more likely. If the swelling is without itching or blisters, lasts longer than a day, and is poorly responsive to antihistamines, a complement screening (C4, C1 inhibitor) is needed. [29]

Are tests necessary for the first episode?
If it's a typical allergic edema with urticaria and a rapid response to therapy, no. For repeated episodes without urticaria, yes, a minimal complement panel is necessary. [30]

Is it true that antihistamines and steroids "don't work" for some types of edema?
Yes, they are almost useless for bradykinin-induced edema; specific medications are required. They are effective for allergic edema, but adrenaline is always the first choice for anaphylaxis. [31]

Can I continue taking an ACE inhibitor after an episode of edema?
No. Stopping it is permanent. Alternatives are considered (for example, angiotensin receptor blockers – the risk is significantly lower, but not zero). [32]

What new treatments for hereditary angioedema have emerged recently?
In 2025, garadacimab (a factor XIIa inhibitor) and donidalorsen (a prekallikrein RNA therapy) were approved for the prevention of attacks in patients aged 12 years and older. This expands the treatment options, alongside lanadelumab, berotralstat, and a prophylactic C1 inhibitor. [33]

Doctor's Block: ICD Codes and Documentation

ICD-10:

• T78.3 - Angioedema (including "allergic edema").
• D84.1 - Defects of the complement system (used for hereditary/acquired deficiency of C1 inhibitor). [34]

ICD-11:

• 4A00.14 - hereditary angioedema; 4A00.15 - acquired angioedema (immunodeficiency section; cluster coding and expanding circumstance codes are used). [35]

Table 9. Quick selection of codes

Scenario	ICD-10	ICD-11
Allergic/unspecified angioedema	T78.3	Allergic Condition Group Code + Expansion Codes
Hereditary/acquired C1 inhibitor deficiency	D84.1	4A00.14 / 4A00.15