If amount they draw influences the crash (does for me), I always go equipped with a table of the minium required draw for each test that I want (or agree to), and go over that and the total I find acceptable to them. I usually look up several different lab requirments for each test for the table. I usually let them know, its how much they fill the tubes, not how many tubes; i ask for a butterfly needle so they can easily switch. So when I was doing ok, I could tolerate 8 ml of blood, and once when i really needed tons of test i waned, I went up to 10ml of blood. The way many people draw blood, that's just 2 tubes and very few tests, but i'm usually able to get a dozen or more tests from them.
Another trick is after you get home, you call up and say I forgot all about X and Y - can you add it? there's almost always blood left over, even with the miniumums being drawn.
Plus if any lab is reluctant, the magic words can be from a doctor who you ask to write down on the order "minium draws".
Also may need to reassure them, yes I understand there may not be enough blood to do "repeat testing" Yes I understand there may not be enough blood yada yada yada
but of course if amount of blood doen'st matter to you, then none of this relevent.
sipping juice before, immeidately after, and even during, can helpw ith the later crash that comes. and going home right after- not stopping anywhere even if you're charged up.
ostly i guess, go through the list of tests and only agree to the ones that you think will advance yoru case. If you don't know anything about such things then alas youre at the mercy of a tired overworked flow chart yielding MD.