How reliable are commercial allergy tests?

The ability to diagnose allergic disease was studied in 9 fish-allergic and 9 control subjects, who provided specimens of blood and hair for testing. All fish-allergic subjects had previously been shown at Guy's Hospital to have a positive skin prick test to fish. The specimens were submitted as coded, duplicate samples to five laboratories which all offer a commercial service in carrying out diagnostic tests for allergy. All five laboratories were not only unable to diagnose fish allergy but also reported many allergies in apparently non-allergic subjects and provided inconsistent results on duplicate samples from the same subject.