Allergy diagnosis is based on a careful clinical review and there are some internationally validated tests (e.g. skin prick tests, specific IgE tests) which when properly performed can help in confirming the diagnosis. There is however, no blood or other test, which by itself can diagnose allergy. The only exception to this is allergy challenge testing, performed under medical supervision in a hospital setting. In particular, there is no scientific basis to tests such as Vega, hair tests, IgG tests or kinesiology. Not only do these tests not work, they may be dangerous, as they can result in the commencement of restrictive diets and the loss of valuable nutrients. The Irish Health Products Regulatory Authority issued an advisory in March 2015 concerning the use of these tests and you can see that here. Do not waste your money on them. If you are worried about allergy, talk to your doctor.