Allergies

Allergy skin testing (skin prick testing)

Skin prick testing is a quick way of detecting the “allergy antibody” (IgE) to specific allergens, usually performed for suspected allergic rhinitis (hay fever), asthma or food allergy. Allergy test results should not be interpreted in isolation; their relevance needs to be considered in conjunction with your medical history.

How is skin prick testing performed? It is usually done on the forearm and sometimes on the back. A drop of the allergen extract is placed onto the skin. A small scratch is then made through the drop with a sterile lancet so that a small amount of the allergen enters the skin. More than one allergen can be tested at one time. If you are allergic to the test allergen, a small, red, itchy lump (wheal) will appear at the site within 15 to 20 minutes.

Skin prick testing is performed using allergen extracts commercially produced by reputable manufacturers. Some of these allergen extracts are not registered by the Therapeutic Goods Association (TGA) in Australia, however Dr Priscilla Auyeung has TGA authorisation to use these products. In some cases of suspected food allergy, fresh food (e.g. seafood, fruit) is also used for skin testing.

What are the risks? Skin prick testing is slightly uncomfortable but is usually well tolerated, even by young children. The wheal resulting from a positive test usually subsides over 2 hours. Occasionally, the wheal can be more severe or prolonged, which indicates that you are very sensitive to the allergen. This may be treated with an antihistamine tablet, a corticosteroid cream and an ice pack. Very rarely, skin prick testing can cause more severe reactions, including anaphylaxis. This is extremely rare when the testing is performed to assess allergic rhinitis (hayfever) or asthma.

Do I need to stop any medications before testing? Antihistamine tablets interfere with allergy skin testing results, and should be stopped for 3 days before testing. Please continue your other medications, including nasal sprays and asthma puffers.

 

Allergic rhinitis (hay fever)

Allergic rhinitis is very common, affecting 3 out of 10 children and adults. It causes sneezing, an itchy, runny or blocked nose, itchy and watery eyes, and can sometimes trigger asthma.

Some individuals are allergic to grass or tree pollens, and their symptoms manifest during the pollen season. In Victoria, the pollen season can start as early as August and can last until February, depending on the pollen. Others suffer hay fever symptoms at other times of the year, and may be allergic to house dust mites or animals such as cats, dogs and horses.

Many people underestimate how significantly allergic rhinitis affects their lives. Symptoms can disrupt sleep, leading to fatigue and difficulty concentrating, and affect work or studies.

Hay fever testing. Your symptoms will first be assessed. If appropriate, skin prick testing can be performed to identify what you are allergic to.

Hay fever treatment. Firstly, avoid the allergen(s) responsible for your symptoms. This is often difficult and sometimes not possible. Many people will require antihistamine tablets, corticosteroid nasal sprays and eye drops. In severe cases, these measures will not be sufficient and some people will need allergen immunotherapy (sometimes also called desensitisation).

 

Food allergy

Food allergy is an increasingly common occurrence, in 1 in 20 children and 1 in 100 adults. The most common food allergies are to cow’s milk, egg, nuts, seafood, sesame, soy and wheat. Food allergy can cause an itchy mouth or throat, hives (urticaria), swelling (angioedema), vomiting, stomach pain, diarrhoea, chest tightness, wheezing, difficulty breathing, dizziness or collapse. Food allergy symptoms usually occur within 1 to 2 hours of eating the food, but there are some exceptions.

The details of suspected allergic reactions are very important. A symptoms diary is always useful, including the following information:

  • Time of symptoms
  • What was eaten or drunk and at what time. Was the food cooked or raw? Include ingredients e.g. bring in the packet, contact the manufacturer or the chef.
  • Whether you exercised after the meal

 

Food allergy testing. After the clinical assessment and if appropriate, skin prick testing can be performed to identify what you are allergic to. Both clinics stock an extensive range of commercial food allergen extracts, including cow’s milk, egg, nuts, seafood, sesame, soy, wheat and others. However, commercial extracts are not available for uncommon food allergens, and are less reliable than fresh food in some cases (e.g. seafood, fruit). In these situations, skin testing is done using the fresh food. Only a small quantity is required (1 teaspoon), with each food item kept separately in small containers of zip-lock bags. For fruit and vegetables, include the flesh, seeds and skin. For seafood or meat, bring separate raw and cooked (e.g. microwave without adding any seasoning, oils or condiments) samples. For the safety of others, please ensure that these food samples are kept sealed while in the waiting room. Sometimes, there may be a medical reason why skin testing is not performed, however it is helpful to have these available in case they are needed. Diagnosing food allergy is not always straightforward. Further assessment with blood tests and a food challenge in the allergy ward is sometimes necessary.

Food allergy treatment. The mainstay of treatment is to avoid the triggering food. Once identified, a plan can be put in place to avoid the culprit food. It is also critical to have an emergency action plan in case of accidental exposure. For some individuals, this includes carrying adrenaline auto-injectors (e.g. EpiPen or Anapen). Regular allergy reviews are important to ensure that these are up to date.

 

Urticaria (hives) and angioedema (swelling)

Urticaria (hives) is an itchy, raised, red skin rash. It affects 1 in 5 people at some time in their lives. One in 10 people who have urticaria also develop angioedema, which is swelling in the deeper tissues such as in the face, lips, tongue or throat.

Urticaria can be acute (up to 6 weeks in duration) or chronic (6 weeks in duration or longer). A number of different conditions can cause urticaria, including allergy, infection, medications and physical stimuli (e.g. pressure, heat, exercise, cold, vibration). In some individuals, the urticaria is “idiopathic”, in which symptoms recur due to no apparent trigger.

As so many different conditions can cause urticaria and angioedema, details of the symptoms are very important. A symptoms diary is always useful, including the following information:

  • What time did you develop the symptoms?
  • Did you eat any food beforehand? Include time of the meal and ingredients.
  • Did you take any medications or supplements beforehand? Bring in a list of your medications and supplements, and what time you take them. Don’t forget those that you may take from time to time, e.g. painkillers and antibiotics.
  • Did you do any exercise or other activity beforehand? Include time of the activity.
  • Did you have any other illnesses at the time, e.g. infection?
  • Does anything worsen the symptoms, such as pressure (e.g. from tight clothing), heat, exercise, cold or stress?

 

Which tests are required will depend on your clinical history. Allergy testing may not be relevant and another type of testing may be necessary. Your treatment plan will depend on the underlying cause of urticaria and angioedema.