Need immediate blood pressure help!

[AD]

Prazosin is a beta blocker I take it.
Works great
http://www.ncbi.nlm.nih.gov/m/pubmed/6110503/

technically, prazosin is an alpha-blocker. but what the hell, it still works.

[Capebuffalo]

I may be way off base here so please tell me. If he is being retested on Saturday and doesn't have time to get any of the items mentioned above. What if he gave blood on Friday afternoon. Will less blood equal less pressure? The body won't replace a pint in 24 hours. Tell me if this is bro science.