While the blood tests can help doctors identify potentially risky foods, they aren't always reliable. A 2007 issue of The Annals of Asthma, Allergy & Immunology reported on research at Johns Hopkins Children's Center, finding that blood allergy tests could both under- and overestimate the body's immune response. A 2003 report in Pediatrics said a positive result on a blood allergy test correlated with a real-world food allergy in fewer than half the cases.