Challenge or provocation tests are tests in which the individual is exposed in various ways to a potential allergen and any reactions are recorded.
Nasal and bronchial challenge tests are used most commonly to test inhaled allergens such as pollens or house dust mites. In the nasal challenge test, a tiny amount of a suspected allergen is applied to the lining of the nose and reactions are recorded. The results are measured by counting sneezes in the first 15 minutes, measuring nasal discharge and by examining the inside of the nose. Instruments measuring nasal airflow can also be used.
In the bronchial challenge test, more sophisticated techniques are used, involving inhaling measured quantities of suspect substances, and then recording reactions and measuring lung function. There is a risk of adverse reaction and these tests are usually done in hospital as an in-patient, in case adverse or delayed reactions occur. Tests of this kind are time-consuming and can be risky.
Oral challenge tests are used to identify food allergy or food intolerance. There are a number of ways to undertake these; and unless you are seriously ill, or have severe multiple allergies, you will be able to do them at home yourself in the form of an elimination diet under medical guidance.
The main principle of an elimination diet is to go on a low-allergen diet, or to fast for some time, and then reintroduce and eat suspect or problem foods, monitoring your symptoms.
Oral challenge tests can be organised on a double-blind basis, so that the food eaten is disguised and neither the person testing the food, nor the doctor or nurse supervising the test, knows what food is being tested. This is expensive and not always easy to arrange – you can disguise lentils easily, but not carrots or beetroot, for instance – so it is not commonly used.