Test result question

My 13 yo son just had labs done after months of intense stomach pain. His doctor said that although his results show a high likelihood of Alpha Gal that we would need to see an allergist to confirm. We’ve already switched his diet ahead of his allergist appointment at the end of June. My question is will the diet switch mess with any tests the allergist may do on him. He also has an appointment with a GI around the same time. Thanks for any advice or information.