Blood draws for my 2 year old SWCAH son are almost always an extremely stressful experience for all of us!  Multiple pokes and digging are usually required to get the vein (and like Chris I always insist upon the "best" phelbotomist at the children's hospital to do the draw).  On one occasion he was so upset I thought he was going to throw up.  This short-term stress, however, does not seem to have affected his blood test results as he is almost always oversuppressed.  If his 17-OHP is increased by the stress of the blood draw, it can't be by much.  Regardless, I would much prefer to do a 24 hour urine collection if I had the option.

My understanding is that 17-OHP gives an idea of what is going on at the time of the blood draw, and the androstenidione gives a longer term picture.  So if the 17-OHP is elevated, but the androstenidione is okay, then the child probably hasn't been undersuppressed for a long period of time.  But I'm not exactly sure about this (or anything else for that matter!).  This is a very interesting subject!