As of right now, she'll just chew at the base of her tail and her back, and itch behind her ears. She has always had slightly watery eyes as well, probably about once a week they get very watery and I end up wiping them numerous times a day. She does have allergies to certain vaccines, as we discovered once her face began to swell about an hour after receiving two vaccines at once... so we always give her Benadryl before vaccines. The issue with that is that she absolutely hates it and no matter what we try, we end up having to hold her and attempting to squirt it down her throat.
I'm curious as to whether the allergies are simply seasonal or if it's food-based. As of right now, she's on Go! Chicken + Turkey + Trout and was on Acana Ranchlands before that. She also gets dehydrated beef tracheas to help clean her teeth, but I wouldn't consider that a major part of her diet since it takes her a week, at the very least, to finish one.
And since it's a blood test, I'd imagine that they could take it while she's sedated for her dental cleaning? She's really good for needles, because she's learned that the vet will cuddle her afterwards, but I don't know if she'd be quite as good for a blood test.