Anaphylaxis: The Urgent Reaction of the Immune System

Anaphylaxis Meaning: What is it? 

Anaphylaxis is defined as a potentially fatal, severe, and systemic allergic reaction that occurs suddenly after contact with an allergy-causing substance. Normally, if you are allergic to a substance, the immune system overreacts to this allergen by releasing chemicals that cause allergy symptoms, these symptoms typically occur in one location of the body. However, some people are more susceptible to a much more serious anaphylactic reaction, and the immune system overreacts to the allergen and affects more than one part of the body at the same time, resulting in anaphylaxis.

Anaphylaxis causes and triggers

Anaphylaxis is the result of the body’s natural defence system (immune system) overreacting to a trigger. The triggers vary between individuals and are not always the same. 
 

Common anaphylaxis triggers include:

• Food - such as peanuts, nuts, fish, shellfish, eggs, milk, etc.
• Medications - such as some antibiotics (penicillin and related antibiotics), anti-epileptic medications, and non-steroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofen)
• Insect stings - particularly wasp and bee stings
• General anesthetic
• Radiocontrast agents - contrast chemicals containing iodine (e.g. X-ray contrast dye)
• Latex - a type of rubber found in some rubber gloves and condom
• Exercise - very rarely, anaphylaxis can occur after physical activity (known as exercise-induced anaphylaxis)
• Mast cell disorders - rare conditions causing the mast cells to become highly active, leading to unpredictable outbreaks of anaphylaxis

In some cases, there may be no obvious trigger, known as idiopathic anaphylaxis.

Anaphylaxis symptoms and signs 

Anaphylaxis usually develops suddenly and deteriorates very quickly, symptoms of anaphylaxis include:

• Breathing difficulties - fast, shallow breathing
• Wheezing
• Swelling of the throat and tongue 
• Itchy, raised rash (hives)
• Swelling underneath the skin (angioedema) 
• Fast heartbeat
• Clammy skin 
• Collapsing or losing consciousness
• Confusion and anxiety 
• Abdominal pain

Anaphylaxis diagnosis

Anaphylaxis is a medical emergency diagnosed mainly based on clinical presentation, to avoid delay in medical treatment.

After the initial stabilization and management, doctors will ask more about what might have caused the condition and perform more tests to identify allergens that caused anaphylaxis. 

The following test may be recommended to help confirm the diagnosis: 

• Blood test - measures the amount of a certain enzyme (tryptase) that can be elevated up to three hours after anaphylaxis. Blood tests to look for the presence of IgE antibodies that bind to specific allergens may be used to aid in confirmation of the body’s response to an allergen
• Skin-prick test - introduction of a tiny amount of each common allergen into the skin by lightly pricking through the surface of the skin, a slight swelling with redness will appear if the reaction is positive. The skin-prick test has high sensitivity and specificity in general but carries limitations for food allergens
• Intradermal skin test - this test can sometimes be used to identify patients with negative skin prick test results and low-level sensitivity
• Challenge testing - challenge testing involves the introduction of an allergen by ingestion, inhalation, or injection to determine the patient’s clinical response. Since it can provoke life-threatening anaphylaxis in highly sensitized individuals, challenge tests must be conducted by an allergist experienced in its use

Anaphylaxis treatment 

Anaphylaxis is a medical emergency that requires immediate treatment, it is life-threatening if not treated quickly.

Acute anaphylaxis management

If someone has symptoms of anaphylaxis, you should: 

• Remove the trigger if possible 
• Use the adrenaline auto-injector (AAI), if the person has one – after making sure how to use it correctly
• Call 999 for an ambulance immediately – even if the person starts to feel better, and mention that you think the person has anaphylaxis
• Lie the person down flat and elevate lower legs - unless the person is having breathing difficulty which prompts the person to remain upright. Place pregnant women on their left side. Place unconscious patients in the recovery position to ensure the airway remains open and clear.

You can follow these steps yourself if you can while having an anaphylactic reaction. People who have had an anaphylactic reaction are at risk for future reactions, therefore it’s important to carry an adrenaline auto-injector (AAI) if you are at risk.

Anaphylaxis: Adrenaline auto-injector (AAI)

You may be prescribed an adrenaline auto-injector (AAI) if you have an ongoing risk of developing anaphylaxis. If so, it’s important to remember the following:

• Carry 2 auto-injectors at all times 
• Check the expiry date of the injector regularly
• Do not delay injecting yourself if you think you may be experiencing anaphylaxis - even if the initial symptoms are mild, it is better to initiate early use of adrenaline than delay treatment until you are experiencing severe anaphylaxis 

Anaphylaxis treatment in a hospital

Even if you feel better after the administration of an adrenaline auto-injector (AAI), you will need to go to the hospital for observation as the symptoms can occasionally return shortly within a few hours after appropriate treatment, even with no additional exposure to the allergen. This is known as biphasic anaphylaxis. 

Treatment while in the hospital includes:

• Supplemental oxygen may be used to help to breathe
• Fluids may be given directly into a vein to maintain blood pressure
• Intramuscular (IM) adrenaline - is preferred over intravenous (IV) as IM is faster and safer. IM adrenaline may be repeated at 5- to 15-minute intervals if there is no response or an inadequate response clinically
• Adjunctive medical agents - such as antihistamines (e.g. cetirizine, famotidine) and glucocorticoids (e.g methylprednisolone) may be given to help relieve symptoms 

Anaphylaxis prevention

The best way to prevent anaphylaxis is to stay away from the triggers. The following can help reduce the risk of having anaphylaxis:

• Identify and avoid triggers - an allergist can perform allergy tests to check for anything that could trigger anaphylaxis
• Be sure to alert all your healthcare providers of medications that you reacted to
• Use caution around insects if you are allergic to stinging insects - wear long-sleeved shirts and pants; don’t walk barefoot on grass 
• Carefully read the food labels if you have food allergies
• Allergen immunotherapy (also called allergen desensitisation) can be performed for allergy caused by food, certain medications, insect venom and animals, in order to prevent future episodes