Food Allergy Tests

Food allergies are usually tested by using various “Elimination” diets in which the suspected foods are eliminated from the diet for several weeks and then gradually re–introduced one at a time, while the person is observed for signs of an allergic reaction. Because food allergies are often affected by what the person thinks they might be allergic to, a double–blind test may be advised. In this test, suspected foods and placebos (inert substances) are given in a disguised form. The person being tested and the health care provider are both unaware of whether the particular substance being tested in that session is a placebo or a food substance (a third party knows the identities of the substances and identifies them with some sort of code). This test requires several sessions if more than one substance is under investigation.

Other Tests

Challenge tests may be carried out in organs other than the skin. Thus, suspected allergens may be inhaled in bronchial or nasal challenge tests and their effects assessed by measurements of pulmonary or nasal airways resistance. It is often difficult to distinguish allergic and irritant responses when these methods are used, but they are sometimes helpful in diagnosing and assessing response therapy. Similarly, oral challenges with specific foods may be of help in the assessment of food allergic disease, usually following a period on a diet, which excludes the allergen. A number of other tests of organic function may, of course, be called for, depending upon the presenting clinical symptoms. End–organ biopsy may also be of help e.g. in many skin disorders in gluten–sensitive enteropathy and in some auto–immune disorders.

Biopsy specimens may be examined histologically and by immunofluoresence techniques. Indirect immunofluoresence, a fluorescein–labeled reagent specific for human Immunoglobulins is used to reveal their deposition in the tissues – most commonly the skin. Indirect immunofluoresence is used to reveal auto antibodies. Here, cryostat sections of tissue containing the relevant antigens are incubated with the patient’s serum. A fluorescein labeled reagent is then added, thus revealing the sites at which Immunoglobulins has become bound to the tissue section.