The second test is called an ImmunoCAP® and involves blood being taken from the patient. The ImmunoCAP test directly looks for the IgE antibodies to specific allergens in the blood. It therefore also shows sensitisation … the potential to have allergy, not the presence of allergy itself. The higher the ImmunoCAP result is, the more likely it is that the person is truly allergic to that allergen rather than just being sensitised.
The blood test is useful because it can be done even when the person has recently had antihistamines. Adults and children of any age can take an allergy blood test.
ImmunoCAP tests are available for hundreds of individual (specific) allergens … grass and tree pollens, mites, moulds, foods, insect venoms, pet allergens, cockroaches and more. The choice of allergen to be tested depends on the history of the illness the person has, the history of any reaction/s and the area in which the person lives. Some allergens are more common in coastal areas, others inland. People living in the country may require testing for moulds (grow in granaries and thatched roofs), mites that grow in vineyards rather than indoors, or specific trees in the area. People living near the sea may require testing for moulds (that can grow on seaweed).
ImmunoCAP tests are also available for mixes of allergens, like lots of nuts all together, or lots of tree pollens or lots of moulds. These can be used to screen for allergy to a group of allergens, rather than a specific allergen.
Two commonly used screening tests are the food mix (containing egg, milk, peanut, fish, soya and wheat) and the breathed-in (aero) allergen mix (Phadiatop) which contains many allergens including mites, pollens, moulds and pets. If these are reactive, it may be useful to do the tests for the individual allergens to see which actual allergen you are sensitised to. This can often be done on the same blood sample without another needle-prick.
Allergens are usually very big proteins. Some parts of the protein cause more severe allergies than other parts of the protein. Newer ImmunoCAP “component” tests can look for specific parts of the allergy protein and indicate whether the allergy is more likely to be severe, less likely to go away or more likely to be a “real” allergy rather than just an “innocent” sensitisation.
Commonly used component tests are used for milk allergy (casein), peanut allergy (Ara h2), Egg allergy (ovomucoid), wheat allergy (omega 5 gliadin), hazelnut allergy (Cor a8), soya allergy (Gly m5), bee allergy (Api m1 and Api m10) and wasp allergy (Ves v1 and Ves v5).