[anonymously]

I never had any blood tests (to identify allergies) done on my dog, just the skin testing by a dermatologist.
The best choice would be to see a board-certified veterinary dermatologist, if one is available near you (here is a list: http://www.acvd.org/).

Most dermatologists will not skin test for allergies until the dog has been exhibiting symptoms for 1 year/4 seasons without any significant periods of relief. There are also other treatment options that a specialist could offer.
Don’t be fooled by mail-in saliva and hair tests, I have heard they are unreliable

A summary of treatments for canine atopy:

Evidence-Based Canine Allergy Treatment

And here is a recent update:

Evidence Update- Evidence-based Canine Allergy Treatment

More info here:
http://www.2ndchance.info/allergytesting.htm
Skin tests to determine what your pet might be allergic to are considerably more accurate, on the whole, than blood tests. However, they are not 100% accurate either. To have them performed, you will need to locate a board certified veterinary dermatologist

excerpt below from: http://www.2ndchance.info/Apoquel.htm
Food Allergies are probably over-diagnosed in dogs (they account for, perhaps 5-10%). Hypoallergenic diets are occasionally, but not frequently, helpful in canine atopy cases but you should always give them a try. Food intolerances are more common – but considerably more likely to result in digestive disturbances and diarrhea than in itching problems.

PS: A lot depends on the expertise of the specialist to get the solution right, regarding allergen specific immunotherapy. Even when it is effective, sometimes the solution has to be tweaked from time to time. And it can take a year or so to see dramatic results. In my dog’s case I saw improvement right away, however, they still have flare-ups…