Anaphylaxis (pronounced ana-fill-ax-is) is a severe and potentially life-threatening allergic reaction. The common causes of anaphylaxis include food, insect stings, latex and medicines, but sometimes there may be no obvious trigger for the reaction.
If after medical testing and investigation the cause of the reaction is not found, the reaction is then labelled as ‘idiopathic anaphylaxis’ (which means ‘cause unknown’). This does not necessarily mean the reaction took place without something triggering it; it simply means that no trigger can be identified.
Sometimes it could mean there is an unusual external trigger, such as a rare food allergen for which there is no skin or blood test, or which tests fail to pick up. Sometimes it means there is no external trigger; instead, the cause is a temporary increase in the reactivity of the immune system. This increased reactivity usually clears up within a few weeks or months, although in some cases the condition may take a year or two to settle. A key message in all cases is to visit your GP and ask for a referral to an allergy clinic.
Mild symptoms may include nettle rash (also known as hives or urticaria) anywhere on the body, or a tingling or itchy feeling in the mouth. There may be lip or face swelling, which is not serious in itself unless any of the more severe symptoms listed are also present.
In extreme cases there could be a dramatic fall in blood pressure (anaphylactic shock). The person may become weak and floppy and may have a sense of impending doom. This may lead to collapse and unconsciousness.
The speed at which life-threatening symptoms occur varies from person to person. Symptoms may begin suddenly and progress quickly.
In general, the first episode of idiopathic anaphylaxis tends to be the most frightening because the person affected has no understanding of what is happening or what to do about it. After that, they may recognise the initial symptoms and act quickly.
It is important to see your GP as soon as possible if you suffer any symptoms that you think may be caused by an allergy. Even mild cases need to be medically assessed because the next reaction, in some cases but not all, could be more severe.
Some GPs have a clear understanding of allergies and similar conditions, but it’s more likely your doctor will need to refer you to an allergy clinic. Guidance issued by the National Institute of Health and Care Excellence (NICE) recommends that following emergency treatment for suspected anaphylaxis, people should be offered referral to a specialist allergy service (NICE clinical guideline 134, 2011). Your GP can locate an allergy clinic in your area by visiting the website of the British Society for Allergy and Clinical Immunology (www.bsaci.org).
Once you get a referral, the consultant will discuss your symptoms with you in detail as well as your medical history. The results of skin prick tests and blood tests may help the specialist identify the cause of the problem. If no cause can be found, then the term idiopathic anaphylaxis is used. Sometimes the cause of the first attack may not be obvious but the trigger can become clearer if you experience further attacks.
Food should be considered as a prime suspect. Foods eaten a few minutes before the start of an attack are the most likely culprits. While it is less likely when food was eaten more than an hour before the start of an attack, there are some rare causes where there is a longer delay such as with red-meat allergy (see below; Delayed allergy to red meat).
The most common food triggers are shellfish, fish, peanuts, tree nuts (such as cashews, walnuts or Brazils), milk, eggs and wheat, although many other foods have been known to trigger anaphylaxis. If a particular food is suspected, but skin or blood tests are unexpectedly negative, the consultant may suggest an oral food challenge test to remove this food from the investigation. This is where you eat a very small amount of the suspect food while under medical observation, gradually building up the amount eaten until symptoms occur or it is shown that the food is not the cause of the reaction. This should never be performed at home. There are also situations where a food allergy only causes a reaction if followed by intense exercising (see below; Food plus exercise).
Prescribed drugs, insect stings and latex may also be considered as the cause of the reaction. Any medication taken for years may suddenly cause anaphylaxis. If skin tests are not available for a suspected medication, you may be required to stop taking it for a short time and then take a test dose. This must be done under supervision in hospital.
A diagnosis of idiopathic anaphylaxis should only be made after an extensive medical investigation. This should include a review of all hospitalisation and A&E records.
So that you can treat severe symptoms yourself, your doctor is likely to prescribe injectable adrenaline (also called epinephrine).
The adrenaline auto-injectors prescribed in the UK are EpiPen®, Jext® and Emerade®, which are designed for self-administration. You should be prescribed and carry two adrenaline auto-injectors at all times.
After adrenaline is administered, someone must always dial 999 in case the symptoms return. Guidelines state that you should lie flat with your legs raised (Resuscitation Council UK, 2008 and BSACI 2017), although this is not recommended if there is breathing difficulty, when sitting with arms anchored makes it easier. If you feel as though you may be sick, your head should be turned to one side. If you feel weak or faint, you must lie-down preferably with legs angled above the head.
You will need to know how and when to use your adrenaline injector, so training should be given by a medical professional such as your doctor, local practice nurse or pharmacist. You can also find help on the website relevant to the injector you carry.
Anaphylaxis can progress rapidly and without early warning signs. Watch out for any combination of the following signs and then act fast:
Use your adrenaline injector, even if unsure. Adrenaline is very safe for everyone but those with underlying heart disease. Even with underlying heart disease, if there are Airway, Breathing or Circulation symptoms, the risk from untreated anaphylaxis is likely to be higher than the risk from adrenaline. Some drugs (such as beta-blockers) can interfere with the action of adrenaline, and these drugs are often avoided in patients who carry adrenaline auto-injectors.
If you carry antihistamines for any reason (for example, to treat hay-fever or hives) bear in mind that these cannot be relied upon in cases of anaphylaxis, even if the symptoms are in their early stages and apparently mild. Oral antihistamine treatment delivers no measurable activity within 30 minutes of the dose, and peak activity is not reached for about three hours. Adrenaline injected into the thigh muscle is the first line of defence in the treatment of anaphylaxis.
If you suffer from asthma – especially if it is poorly-controlled – it is likely to increase the severity of an allergic reaction. If you have asthma, go to your GP and request a review of your asthma to ensure that you are using the most effective treatment.
Some cases of idiopathic anaphylaxis have an internal cause – a temporary increase in the reactivity of the immune system. Cases in which attacks are occurring frequently may require a few weeks or months of regular treatment such as a daily oral antihistamine or steroid to prevent further attacks and help the condition to settle down. Anaphylaxis may occur for up to two years before finally burning itself out.
We advise people who have experienced anaphylaxis – whether the cause is known or not – to wear a medical identification bracelet or talisman.
Finally, we believe it is important to let your family, friends or work colleagues know where you keep your adrenaline injector and what needs to happen in an emergency. In the case of children, the school will need a written care plan and staff must be trained in the use of the injector.
When someone suffers a suspected allergic reaction, they may be tempted to consider one of the common food allergens as the culprit, such as peanut or shellfish. Indeed, this may prove to be the case, either because the allergen was present in the food eaten or because of cross-contamination somewhere in the food production process. However, the cause of the problem may be less obvious. A few possibilities are presented here.
For a small minority of people, anaphylaxis can occur when a combination of factors is present together. This makes diagnosis difficult and without a thorough investigation the symptoms may be classed as idiopathic. Here we give a few examples taken from medical literature.
Note that although angioedema is a condition in its own right, it can also occur during anaphylaxis and with other conditions such as spontaneous urticaria.
If you suffer allergy-like symptoms but the cause is a mystery, keep a detailed account of your experience. Important points to note down are:
All these details might help to build a picture of the problem and possibly identify a common thread.
Some other things to consider
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