Immunoglobulin E, also known as RAST, is useful when immediate allergy to a food or natural inhalant allergen(s) is suspected. The test is available in some NHS hospitals and GP practices but training to interpret these results and offer appropriate advice could improve. Not helpful in identifying other food reactivities or intolerance. Broadly speaking the IgE results correlate to the findings of skin prick tests.
When a person's circumstances are inappropriate for various forms of exclusion diets or the diet is too restricted, we use blood tests which focus on allergic or "non-allergic" food reactivities. These, though far from perfect, can offer very helpful guidance on how to improve one' s diet.
Allergy or sensitivity to environmental chemicals is usually investigated with blood tests which scrutinise the effects of various types of hydrocarbons, organophosphates and chlorinated compounds on lymphocytes blood cells, known to be involved in chemical sensitivity. A large number of toxic substances can be tested this way including mercury, nickel, benzene, toluene, lindane and so on.
A host of other tests are also available, depending on the conditions under investigation, including tests to identify nutritional deficiencies such as vitamins, minerals, essential fatty acids, tests for adrenal or thyroid function, tests to assess risk of osteoporosis, cardiovascular disease or cancer, tests for various malfunctions of the cell chemistry, the immune system and so on.