Anaphylaxis: a case-based approach

The case: a sudden reaction

Imagine Aisha, in her twenties, at a friend's birthday meal. Minutes after eating a dessert she feels her lips tingle, then her tongue and throat begin to swell. A blotchy, itchy rash spreads across her chest, she becomes wheezy and short of breath, and she feels light-headed as if she might faint. She has a known nut allergy but thought the dish was safe. Her friend notices she is struggling to speak and looks pale and clammy. This combination — a sudden onset, problems with breathing and circulation, and skin changes after a likely trigger — is the classic picture that should make anyone think of anaphylaxis and act without delay.

Recognising anaphylaxis

Anaphylaxis is diagnosed clinically, not by waiting for tests. The key is a sudden reaction with life-threatening Airway, Breathing or Circulation problems, usually with skin or mucosal changes such as hives, flushing or swelling. Airway signs include throat tightness, a hoarse voice or noisy breathing. Breathing signs include wheeze, rapid breathing and low oxygen. Circulation signs include a fast heartbeat, low blood pressure, dizziness or collapse. Skin changes alone are not anaphylaxis, and their absence does not rule it out. Common UK triggers include foods such as nuts, shellfish and milk, insect stings, and some medicines. Onset is usually fast — within minutes to a couple of hours of exposure.

Immediate management

The single most important treatment is adrenaline, given into the outer thigh muscle as early as possible; it is safe and can be repeated if there is no improvement. In the community this means using an adrenaline auto-injector without hesitation. Call 999 and say the word anaphylaxis. Positioning matters: someone with breathing difficulty may prefer to sit up, but anyone who feels faint or has low blood pressure should lie flat with their legs raised, and a pregnant person should lie on their left side. Never suddenly stand or sit them up, as this can worsen a dangerous drop in blood pressure. Give supplemental oxygen and monitor closely while help is on the way.

In hospital and afterwards

In hospital, the team reassesses Airway, Breathing and Circulation, gives further adrenaline if needed and supports blood pressure with fluids. Older add-on medicines such as antihistamines and steroids are now considered secondary and are not a substitute for adrenaline. Because symptoms can return hours later — a biphasic reaction — patients are observed for a period based on how severe the reaction was before being discharged. A blood test measuring mast cell tryptase, taken soon after the reaction, can help confirm the diagnosis later. Before leaving, people should receive two adrenaline auto-injectors, training on how and when to use them, a written plan and referral to a specialist allergy clinic.

Living safely with allergy

After anaphylaxis, prevention becomes central. Identifying and avoiding the trigger is the priority, supported by allergy testing at a specialist clinic. People at risk should carry two in-date auto-injectors at all times, and family, friends, schools or workplaces should know how to use them. Reading food labels, asking about ingredients when eating out and wearing medical-alert jewellery all reduce risk. It is vital to understand that using an auto-injector is never the wrong choice if anaphylaxis is suspected — delay is the real danger. Regularly checking expiry dates and replacing used or out-of-date devices keeps this safety net working when it is needed most.