Most people think of allergy testing as a skin-prick test, but this isn’t the test I prefer. This is because skin-prick tests identify IgE antibodies only. IgE antibodies cause immediate hypersensitivity reactions, and while this is very useful to know (it may keep you out of the hospital!), it will miss a good 90% of food sensitivities. This is because most food sensitivities trigger IgG antibodies, which have a 72 hour window in the body. This means you can eat something to which you are sensitive, and not react to it for a few days!
IgG testing is a blood test, and it’s never covered by insurance, unfortunately. But for patients who aren’t able or willing to do the elimination diet (which is as cheap as your grocery bill, but it’s a pain), the blood test is definitely worth it. The serum test I use also checks for IgE antibodies to foods at the same time.