robinw my dd went to a paediatric allergist and he wouldn't do a skin prick for peanut since we already suspected it, as it can be dangerous for someone who is highly allergic to it. He did blood tests for dairy, peanut, dustmite and grasses; skin prick tests for beef, chicken, tuna, dog, cat and egg. The blood tests took about a week to come back but the skin prick results were almost instant - we waited about half an hour in the waiting room. She had big red welts for egg, dog and tuna! But nothing for the others (we had suspected cat).
There is a measurement they do in the blood test that indicates their sensitivity to allergens in general. The average level in a "normal" person is about 50 - dd was over 3000! She is highly allergic, and the peanut and dustmite came back positive, although surprisingly the dairy and grasses didn't. She now wears a medic alert bracelet for the peanut. He did say that some things are more accurately tested by ingestion and that skinprick tests aren't always 100% - things like tomato, citrus and wheat for example. All the best, hope it gives you some answers.