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Frequently Asked Questions Archives - LACK

Which is the best test for allergy? Skin testing or blood testing?

  • The short answer is that both complement each other. There are defined circumstances where one test will perform better than the other. Thus, if a child skin is covered in eczema it may be too distressing for the child and inaccurate to do skin prick testing. Here blood testing is the test of choice.
  • Similarly, if a child is on antihistamine medication, blood testing is more helpful as the skin will not react. In contrast, if a child is very allergic and has a high total IgE level, blood testing may produce a high number of falsely elevated results especially to foods such as wheat and soy (so called false positives). Furthermore, skin prick testing allows one to assess the difference in reactivity between a cooked food allergen and a raw food allergen.
  • There are frequent situations where it is helpful to follow both. For example, reduction in both skin tests and blood tests over time is helpful in monitoring the resolution of an allergy.

Frequently Asked Questions Archives - LACK

Which allergens are available for testing?

  • There is no limit to the number of allergens that can be tested. However, most allergies are caused by a restricted number of allergens (common allergic proteins). These include food allergens and respiratory allergens.
  • Food allergies that we test for include: Egg white, cow’s milk, peanut, sesame, codfish, wheat, soy and kiwi. We also frequently test for tree nuts (almond, hazelnut, walnut, brazil nut, cashew nut, pistachio, macadamia nut, pecan nut and pine nut); if you wish to test to a wide range of fish and shellfish we may ask you to bring small pieces of individual fish and shellfish to the clinic, as it is more accurate using the fresh food.
  • Respiratory allergies (those that cause hay fever and asthma) typically include house dust mites, cat, dog, horse, moulds, grass, weeds and tree pollens. More detailed panels can be tested to a wide range of animal danders (e.g. mice, hamsters, guinea pigs, rabbits). Specific pollens present only in countries outside the UK can also be tested (e.g. Ragweed in the United States, Parietaria and Olive pollen in Mediterranean countries)
  • Drug allergy testing is more limited. Very often, no blood test or skin test is available and a challenge in hospital may be required in order to make a diagnosis.

Frequently Asked Questions Archives - LACK

Why see an allergist?

You should see an allergist if you or your child suffer from any of the following:

  • Eczema: Patients with eczema should see an allergist if they:
    • Start with eczema in the first six months of life
    • Have eczema resistant to treatment.
    • Have eczema that shows seasonal variations
    • Have eczema and suspect an allergic cause.
  • Allergic Conjunctivitis: You should see an allergist if medications are not controlling your ocular symptoms.
  • Anaphylaxis: If you/your child have had an anaphylactic reaction (very severe allergic reaction) associated with a food or drug or if the trigger has not been identified.


  • Food Allergy: If you have food allergy, you should see an allergist if you have:
    • Multiple food allergies.
    • Co-existent food allergy and asthma
    • If you are on a restricted diet because of food allergy
    • If you are expecting a baby and want counsel on preventing or identifying food allergies
    • If your child is wheezing and you suspect allergic asthma

Your GP can deal with most allergies by prescribing appropriate medicines and advice. In many cases, the GP may decide that you our your child will benefit from being referred to a specialist in allergies. You should look for medical advice if you or your child present with any symptom of an allergic disease. Many people start self-treating their allergies with over-the-counter drugs. However, these medications may have unpleasant side effects or they may not improve the symptoms.

  • Insect Hypersensitivity: Those individuals who have severe reactions to insect stings or bites.
  • Asthma. The following patients with asthma should see an allergist:
    • Patients with severe asthma.
    • Patients who have both asthma and food allergy
    • Asthmatic patients who believe allergic triggers are causing their asthma
  • Allergic Rhinitis: A patient with allergic rhinitis (hay fever) should see an allergist if:
    • Medications are not controlling your symptoms.
    • Your quality of life is affected
    • If you are interested on immunotherapy (desensitisation)
  • Sinusitis: Individuals with prolonged or frequent sinus infections.
  • Drug Allergies: Those with a suspected drug allergy who are likely to need that drug again.
  • Urticaria (Hives): Patients with urticaria, hives (nettle rash) should see an allergist if:
    • Urticaria is severe
    • Patient suspects it is caused by a food or a drug
    • Hives lasting 6 weeks or more

Frequently Asked Questions Archives - LACK

What should you eat during pregnancy and breast feeding?

There is no evidence that avoiding any food during pregnancy and during the period of breast-feeding will prevent the development of food allergies in your baby.

It is very important that you have a healthy well balanced diet during these important periods. For example, avoiding milk could predispose you to osteoporosis. Therefore, no major dietary changes should be undertaken without consulting your doctor or a dietician.

For further information on eating during pregnancy, visit the Food Standards Agency website.

Frequently Asked Questions Archives - LACK

Why have allergies and asthma increased?

  • Recent epidemiological studies in the United Kingdom and North America have shown that prevalence rates of food allergy in children have increased. In the United Kingdom the incidence of common allergic diseases has trebled in the last twenty years, to become one of the highest in the world. About 20% of schoolchildren in the UK suffer of asthma, about 15% rhinoconjunctivitis, 10-16% eczema and 6-8% food allergies.
  • The increase in peanut allergy has been remarkably high. Recent studies have found that peanut allergy prevalence in the UK is 1.8% and affects 1:50 children in schools.
  • There are many theories that try to explain the rise in allergies during the past few decades.
  • In general, allergies are associated with the Western style of life. For example, the hygiene hypothesis suggests that the lack of early childhood exposure to infectious agents, gut flora and parasites increases susceptibility to allergic diseases by modulating immune system development.
  • It has been argued that either excessive vitamin D or conversely vitamin D deficiency has led to increased allergies. It has also been argued that the decrease in consumption of fresh fruit and vegetables (containing anti-oxidants) in the United Kingdom might account for allergies, particularly asthma.
  • The dietary fat hypothesis argues that reduction in consumption of animal fats and corresponding increase in the use of margarine and vegetable oils has led to the increase in allergies.
  • There is much debate as to whether early weaning with allergenic foods such as cow’s milk can increase the risk of allergies and asthma. There is some evidence that exclusive breastfeeding for the first four months of life protects against allergies but there is no convincing evidence that allergen avoidance beyond 4 months of age is beneficial. Indeed, it has been argued that early introduction of foods such as peanut may lead to tolerance and protect against of the development of peanut allergy. These theories are currently being tested in the LEAP study ( and the EAT study (

Frequently Asked Questions Archives - LACK

What is the “allergic march”?

  • The term “Allergic March” describes how allergic diseases progress throughout the life of an allergic individual.
  • This usually begins within the first few months of life with eczema. In 30 to 50% of these children, eczema is associated with food allergy. Food allergies generally begin to appear within the first three years of a child’s life. As children grow up, the allergic march may progress to the development of rhino-conjunctivitis (hay fever) and/or allergic asthma.
  • This pattern of development of allergic diseases is commonly seen in individuals with a family history of allergy. Frequently, allergic individuals suffer from multiple allergic conditions (eczema, hay fever, food allergies, asthma) which affect their quality of life. For example, a plethora of symptoms varying from itchy skin to sneezing, snoring, wheezing may result in reduced exercise tolerance, poor sleep and concentration and impaired performance at school or at work.

Frequently Asked Questions Archives - LACK

What is an allergy?

  • An allergy is an overreaction of the body’s defence system (the immune system) to one or more substances such as food proteins or pollens that are normally innocuous to most people. These substances are known as allergens.
  • In people with an allergy, the immune system treats these allergens as intruders and attacks them, resulting in the production of antibodies called Immunoglobulin E (IgE). These antibodies bind to specialised cells (mast cells and basophils) that release substances into the body to defend against the allergen causing an immediate allergic reaction.
  • This reaction usually causes symptoms in the nose, eyes, lungs, throat, sinuses, ears, cardiovascular system, skin or the stomach. A subsequent exposure to that same substance will elicit this allergic response again.

Frequently Asked Questions Archives - LACK

What is allergen immunotherapy?

  • Allergen immunotherapy is a long-term treatment for allergic rhinoconjunctivitis (hay fever). It helps to reduce allergic symptoms triggered by the exposure to an allergen (e.g. Pollen). Paradoxically the treatment consists of exposing the patient to increasing quantities of the allergenic substance that causes the symptoms. Immunotherapy consists of introducing small doses of an allergen that the patient is allergic to – this helps the body to overcome the allergy by teaching the immune system to react to allergens in a different way. These changes on the immune system take time and last after treatment has stopped. Immunotherapy may be particularly useful when tablets and/or nasal sprays containing antihistamines or steroids have failed to effectively control the symptoms.
  • Specific immunotherapy is the only treatment that may alter the natural course of allergic diseases whereas other therapies only suppress the symptoms. Allergen immunotherapy reduces symptoms and the need for medications, prevents the development of asthma, reduces the chances of new sensitisations to allergens developing and improve the quality of life.
  • This treatment can be administered under the tongue (sublingually) or by monthly injections under the skin (subcutaneous). Subcutaneous injection immunotherapy has been shown to be highly efficacious for allergic rhinitis and asthma, but its use is restricted to specialist centres. Sublingual immunotherapy should be also initiated by a specialist, but can then continue to be safely administered at home.
  • Subcutaneous immunotherapy is started at very low doses. The dose is gradually increased on a regular basis, until a “maintenance” dose is reached (4-6 months of weekly injections). Once the maintenance dose is reached, the injections are normally given once per month for 3 years. After successful completion of immunotherapy, long-term protection can be expected for a period. Itchiness, swelling, and redness at the site of injection are expected. Systemic reactions such as generalised urticaria (hives) or anaphylaxis occur rarely and need to be treated immediately.
  • Sublingual immunotherapy has been shown to be effective to treat allergic rhinitis and allergic asthma in children and adults and has a very good safety profile. SLIT is taken as drops or tablets, placed under the tongue every day. The first dose must be given at your specialist office under close supervision. The side effects of sublingual immunotherapy are generally mild and limited to local reactions (oral pruritus, edema of the mouth, throat irritation, ear pruritus, sneezing, and swelling of the mouth). These usually decrease within a few weeks and are easily managed with antihistamines.
  • The route of immunotherapy method choose depends on the specific allergic disease, type of allergen triggering the disease, risk of adverse reactions, allergen availability and patient preference. Sublingual immunotherapy is prescribed more frequently because of the ease of administration.

Frequently Asked Questions Archives - LACK

Is immunotherapy the same as homeopathy?

  • No. Immunotherapy is not homeopathy. Allergy vaccines (under the tongue or injections) are produced from standardised allergens, contain a known amount of the major allergen and they have been evaluated in large number of clinical studies.
  • Immunotherapy extracts contain high concentrations of the allergen (allergic protein) and the aim is to build up to a high dose. In contrast, homeopathy is unproven in the treatment of allergic diseases, and relies on progressive dilution of the allergen. The “most potent” homeopathic treatments contain no allergen.

Frequently Asked Questions Archives - LACK

Interpreting the allergy test results

  • When a person presents with symptoms suggestive of allergy, then tests can either narrow down or rule out other causes. There are three medically accepted tests, which can be helpful to evaluate a patient who may have allergy. They are the skin prick tests (SPT), blood tests and challenge testing. However, the history of symptoms is very important and this needs to be taken into account when any of these tests are interpreted.
  • Blood tests and skin prick tests are methods that detect IgE antibodies (these are the allergic antibodies). Blood testing for IgE antibodies (also known as RAST testing) measures the levels of allergic antibodies directly in the blood. A positive skin test indicates indirectly the presence of IgE antibodies in the skin. Both methods complement each other and are often used together to help diagnose allergies. There are however some circumstances where skin testing is more suitable than blood testing and vice versa.
  • Skin test results are expressed as the diameter of the allergic wheal (in mm). Blood tests levels are expressed as concentrations of allergic antibodies in the blood (International Units/mL). The size of the blood test and the skin test do not indicate the severity of the allergy. They do however indicate the probability of being allergic
  • For example, a large skin prick test diameter to peanut of 10 mm and a high blood test level of 30 IU/mL means that the child almost certainly has peanut allergy
  • A skin test to peanut of 0 mm and a blood test level of 0 make it highly unlikely that the child is allergic. However, there is a possibility that your child is allergic despite negative tests, especially if your child has had an allergic reaction previously.

Frequently Asked Questions Archives - LACK

How is skin testing done?

  • The procedure involves the placement of a small drop of the allergen on the skin (usually the patient’s forearm), then a specialist nurse will prick the skin gently using a small lancet.
  • In allergic individuals, this will elicit a localised wheal and flare response after 10 to 15 minutes. Some patients experience localised itching, but any reaction generally disappears within 30 minutes. Usually, 10 to 16 individual tests would be done in one visit.
  • Two control tests are always run thus in order to properly interpret skin tests. The negative control (salt water) must not produce a response whereas the positive control should produce a wheal and flare.
  • Negative control involves pricking a drop of salt-water on the skin to ensure that the skin is not overly reactive; for example, some patients will come up positive to every single skin test because they have sensitive skin.
  • Positive control: a small drop of histamine solution is placed on the skin to determine that the skin has the capacity to react and produce a wheal or flare response. Antihistamine medication will prevent the skin from reacting to the positive control and other allergic tests which is why antihistamine medications must be stopped before the visit.

Frequently Asked Questions Archives - LACK

Food challenge test

  • A food challenge is the best and definitive way to know if a person has a food allergy. The test consists in giving small but increasing amounts of a suspected allergen (approximately every 20 minutes). If the patient presents with a reaction, the challenge is stopped and the patient is considered allergic to that food and they need to strictly avoid it. When no reaction occurs to any of the doses of food, the patient will receive a full serving of the food. If they can tolerate a normal portion size for their age then the patient is considered to tolerate the food and is encouraged to continue eating it at home.
  • This test is always performed in a hospital and the person is monitored carefully for signs and symptoms of allergy. After finishing the challenge, the patient needs to stay for a period of observation after the final dose to ensure there is no delayed reaction.
  • If the patient is taking any of the medications, please see the section on allergy medications
  • Please bring lunch for you and your child. He/she may be permitted to eat lunch/snacks approximately one hour after the last dose of food is given.

Frequently Asked Questions Archives - LACK

Do allergy tests hurt?

  • Skin prick tests are not painful. Young infants are not bothered by the actual testing, but may dislike having their arm kept still during the period of testing (about 5 minutes). Older children may be fearful of the tests and the allergy nurse will be very reassuring and explain to them that the test is not painful.
  • Allergy tests are safe and do not cause severe allergic reactions or anaphylaxis. If a large local reaction causes severe itching, we will offer the patient antihistamine syrup which rapidly relieves the discomfort. Rarely, symptoms of runny nose and eyes will occur and these symptoms are also easily treated by antihistamine.
  • Some patients may require blood tests. This procedure is performed by an experienced phlebotomist. To ease the discomfort of taking blood, we can apply a “numbing cream” as a surface anaesthetic prior to blood sampling. The cream (Emla) is applied to a small area of skin and then it is covered with a small clear dressing. The cream will be left on the skin for up to 1 hour. After 1 hour the cream will be wiped off. Emla cream numbs the skin so that the patient should not feel the needle being inserted. The cream is safe, but it should not be given if your child has had a previous adverse reaction to the cream.
  • Taking blood is extremely safe. Sometimes it may leave a small bruise which will rapidly improve within a couple of weeks
  • Babies may be more settled if they have the comfort of a pacifier, bottle, toy or teddy bear. Older children may bring along MP3 players to listen to music. Older children and teenagers are encouraged to lie down if in the past they have felt anxious or faint during medical testing.

Frequently Asked Questions Archives - LACK

Can young babies be allergy tested?

  • Yes. Food allergies can already be detected in the first 6 months of life. There is no lower age limit to detect food allergies.
  • If your baby is only a few months of age and has symptoms, allergy testing can be very helpful. The only limitation is that young babies are smaller and there is a limit to the number of tests that can be applied.

Frequently Asked Questions Archives - LACK

Must I stop allergy medications prior to allergy testing?


  • Antihistamine medications must be stopped before skin prick testing and performing a food challenge. However antihistamines do not need to be stopped before blood testing.
  • Short-acting antihistamines such as Piriton [Chlorpheniramine], Ucerax [Hydroxizine], Benadryl [Acrivastine] should be stopped 48 hours before skin testing.
  • Long-acting antihistamines such as Claritin [Loratadine], Neoclarytin [Desloratadine], Zirtek [Cetirizine], Xyzal [Levocetirizine], Telfast [Fexofenadine] need to be stopped 5 days before testing.
  • Cough preparations for children frequently contain antihistamines and you should check for this and if they are present stop the cough preparation 48 hours before the visit.
  • Oral, nasal or inhaled steroid medications do not need to be stopped as they do not affect the test result.
  • Anti-leukotrienes such as Singulair [Montelukast], Accolate [Zafirlukast] do not need to be stopped as they do not affect the test result.
  • If in doubt, please contact the practice.