Frequently Asked Questions

Does reducing exposure to allergic triggers help?

Yes. Reducing exposure to one or more allergic triggers can help reduce symptoms and the need for medication (1). This can only be accomplished by knowing your patient's unique allergy profile.

What is the difference between food allergy and food intolerance?

It is common to confuse the terms food allergy and food intolerance. However, they do not mean the same thing. Food intolerance, unlike food allergy, does not involve the immune system and is not life-threatening. Lactose intolerance, trouble digesting the milk sugar lactose, is a common example. Symptoms usually include bloating, abdominal cramps and diarrhea.

Food allergy, on the other hand, does involve the immune system. It occurs when the body produces IgE antibodies to a certain food. Common symptoms are hives and asthma.

Can an allergic patient develop allergies to new allergens throughout life?

The development of allergy in relation to age can be described as an "allergy march". This means that there is often a given direction, once atopic immune responses associated with IgE antibodies have been initiated and induced the atopic state.

The manifestation of atopic disease varies considerably with the age of the child, as do the allergens involved. In infancy allergies to foods seem to be the most common, after the age of 3 allergy to inhalant becomes predominant. New causative allergens could be added due to higher concentrations of exposure, or as quite new allergens. However, the immune system tends to be less active in older days (2).

What is the prevalence of allergy?

Around 35% of the population have allergic symptoms, although the frequency of allergy may vary from one country to another.

Why do some people become allergic and others not?

Genetic factors determine how easily and how strongly the individual will become sensitized and how much IgE antibodies will be produced. Sensitization, inflammation and irritation of tissue may develop differently in individual patients, subsequent to different exposures.

Why is it not possible to test for contact dermatitis with a blood sample?

Contact dermatitis is not mediated by antibodies but by lymphocytes. Instead a patch-test with a panel of suspected antigens can be used. It is put on the back of the patient for 48 hours and the reactions are finally read after 72 hours. (This type of reaction is also called delayed hypersensitivity).

Is it possible to "grow out" of allergy?

The child usually grows out of milk and egg white allergy, while allergies to foods such as nuts and fish tend to remain in later years. Specific IgE-antibodies to food allergens in younger years constitute an early predictor for developing atopic disease and for IgE production to inhalant allergens later in life.

What is the incidence of allergy to drugs?

The incidence of adverse reactions to drugs of the overall adult population is estimated to be around 15%. Numerous mechanisms are implicated in drug allergy and the incidence of immediate drug reactions (Type I) seems to be very low in comparison with allergy to more common allergens such as pollens and pets. The incidence of allergy to penicillins is 1/1000 administrations, i.e. 0.7 to 10% of treatments (3).

Can you become allergic as an adult, even if you have never been so before?

Yes, one can become allergic throughout life, but the symptoms more often occur early in life. However, it could happen later in life due to the introduction of new allergens or an increased allergen load.

Do skin prick tests (SPT) and IgE determinations give different results?

Skin tests and blood tests are both used to diagnose IgE-mediated reactions to allergens. A positive test depends not only on IgE antibodies, but also on mast cell integrity and vascular and neural responsiveness. Under ideal conditions, skin prick/puncture testing provides results concordant with optimized in vitro IgE antibody tests. However, skin tests are not quantitative, and the result cannot be compared between clinics. In contrast to in vitro tests, skin tests depend on the status of the skin, and are influenced by medication and by the way the test is performed. There is a small but definite risk of systemic reactions induced by skin tests (4).

Another difference is the standardization. SPT results depend on the quality of the extract, the skill of the person performing the test, the location of the skin test site, and on medical treatment. To achieve good standardization, all these parameters must be well controlled, which is not easy. In contrast, ImmunoCAP IgE determinations are standardized by the test manufacturer and the testing laboratory is assessed by means of international or national quality assessment programs such as NEQAS in the UK. This ensures excellent standardization.

Does food allergy play a role in atopic dermatitis/atopic eczema?

Over 30% of children with atopic dermatitis may have food allergy (5). In adults the figure is somewhat lower (6).

What does "hidden" allergens mean?

It is particularly important for children and adolescents to be aware of "hidden allergens" in different foods, i.e. allergens in foods that are not visually seen or fully declared. This group of young people is especially vulnerable to commercially prepared foods where the risk of hidden allergens is greatest. It is therefore important to educate patients to read and understand food labels. Unfortunately, there are examples of misleading food labels and incomplete lists of ingredients.

There are also examples of cross-contamination of food. Since accurate labels alone will not suffice, patients (and others responsible for caring for the young) must be equipped and taught to manage their acute, unexpected anaphylactic allergic reactions to ingested allergens. Peanut, nuts, milk, egg, and seafood are the foods most often implicated in unexpected anaphylactic reactions.

Can there be cross-reactivity between foods?

If patients are allergic to one food, they may also show reactivity to other foods belonging to the same biological family. Foods contain a lot of different allergens, and a patient may be sensitized to one or a few of these. Furthermore, one food might contain the same allergen as another, although it is never certain that a patient will react clinically to both foods.

The most well-documented cross-reactivity is the one which occurs between apple and birch pollen. Nevertheless, all apple allergics are not necessarily allergic to birch pollen. Cross-reactivity can never be assumed. Under no circumstances should important foods be eliminated from the diet without appropriate testing and clinical diagnosis.

Are IgE antibodies stable in serum samples?

Studies have shown that IgE antibodies are stable in serum samples after storage at -20º C for years.

Can plasma, hemolytic, lipemic and icteric samples be used in ImmunoCAP for IgE testing?

Studies have been performed of EDTA-, heparin-, and citrate-plasma, as well as of hemolytic, icteric, and lipemic samples. No significant difference in the results was found using these types of samples, compared to serum.

Can serum extracted from capillary blood be used for IgE testing?

Yes, serum from capillary blood and serum from venous blood will give identical results when testing for total IgE, specific IgE and Phadiatop in ImmunoCAP (7, 8, 9).

Can wood dust cause allergy?

Most wood dusts contain a variety of chemicals causing irritation and, presumably, type IV (T-cell) sensitization, but are not generally known to be involved in IgE mediated reactions. There are some exceptions, however. Some types of tropical wood have for instance been shown to cause IgE mediated reactions.

Does heat-treatment of patient sera influence the IgE test results?

When samples are heat-treated, some proteins undergo steric changes that can be irreversible or partly irreversible. Very high temperatures (boiling) can destroy the proteins completely.

It is known that some parts of the IgE molecule (e.g. the receptor binding part) change their conformation during heat-treatment (56° C for 30 minutes).

In ImmunoCAP tests for total IgE (tIgE) and allergen specific IgE (sIgE) stable epitopes of the IgE molecule are used for the anti-IgE antibody conjugate attachment. Mild heat treatment therefore has no influence on the IgE test results.

From what age is it relevant to perform IgE testing in children?

IgE is present in the circulation at birth, although normally in very low concentrations. In some countries total IgE screening programs, for detection of children at risk for future allergy problems, are carried through on newborn babies. Expected values for children from the age of 6 weeks have been determined for ImmunoCAP Total IgE.

Capillary blood can be used for testing.

Cow’s milk is a major cause of adverse reaction in infants. Reports of the prevalence of IgE-mediated reactions to milk in infants range from 0.5–7.5 %.

Allergy to egg is also very common in infants.Egg-specific IgE antibodies are usually the earliest antibodies appearing in children developing atopic disease . Measurement of egg white specific IgE (Pharmacia CAP System) at 6 months of age has been shown to be a very effective predictor of allergy to house dust mite during the first 5 years of life.

Expected values for specific IgE are not age-dependent.

If a patient has specific IgE antibodies to a particular allergen in his serum, does this always mean that he has clinical symptoms?

The detection of IgE antibodies indicates that the sensitization process has been initiated. Along with symptoms and a positive case history it confirms the causative allergen, but without symptoms it may predict later development of allergic disease. It is often seen that specific IgE antibody responses are preceding the symptoms, but the symptoms catch up with time. In children it could also be seen that the IgE antibodies, i.e. to cow’s milk, remain in the serum for a period after tolerance has been induced.

Is it useful to test specific IgE for food allergens in serum in older children and adults?

Even if food allergy is more frequently seen in infancy, it occurs at all ages. Negative test results give valuable information as unnecessary elimination of food from the diet can be avoided.

What are the principles for quality control and standardizing of ImmunoCAP allergen source materials at Phadia?

Standardization is based on the use of a panel of patient sera for which IgE antibody screening and immunoblotting have been performed. A reference source material is chosen after comparison of at least 5 different lots against these sera. Whenever a new lot of source material shall be taken in use, it must meet the specifications of the reference source material. Thus, in combination with ImmunoCAP quality control specifications for performance, maximal reproducibility is obtained. 


  1. NIH. Guidelines for the Diagnosis and Management of Asthma, 2007. NIH publication 08-4051.
  2. Niemeier NR, de Monchy JG. Age-dependency of sensitization to aero-allergens in asthmatics. Allergy 1992;47:431-5.
  3. Daniel Vervloet, Michel Pradal. Drug Allergy. Sundbyberg: S-M Ewert AB, 1992:4, 55.
  4. Nelson HS. Variables in allergy skin testing. Allergy Proc 1994;15(6):265-8
  5. Sampson HA. The role of food allergy and mediator release in atopic dermatitis. J Allergy Clin Immunol 1988;81:635-645.
  6. Ring J. Nahrungsmittelallergie und atopische Ekzem. Allergologie 1984;7:300-306.
  7. Liappis, N; Berdel, B. Determination of total IgE and of specific IgE in the serum of capillary blood. Allergologie;1998;11:10-12.
  8. Lilja, G; Magnusson C G; et al. Neonatal IgE levels and three different blood sampling techniques. Allergy;1992;47:522-526.
  9. Bauer, C; Atopy screening in children: Total IgE, Phadiatop, and RAST multiple food allergen disc performed on capillary blood samples. Allergologia e Immunologia Clinica; 1987; 2:95.


As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.