Hard Stick -Pain Tolerance

This recent medical experience between the hospitals an the nursing homes has proven I am what all the nurses and aids call a 'hard stck'.  When they go to draw blood or do IV's my veins disappear or once they find them dry up. Sometimes they bust and the IV drug leaks into the skin and they needed to do an antidote.  Eventually, this problem was solved with the addition of a pic line a permanent line inserted in the vein. 

I had two Pic Lines one on the initial one was in the right arm and the second one new one is in the left arm .  My left shoulder  is the one that had the operation where the infection was removed from and I guess it is supposed to be sore.  The Nurses here at the nursing home always comment with as much as had been removed in terms of flesh and old muscle I should be in pain. Actually if I were normal I am  in pain most likely but don't feel it. 

As usual I don't bleed show black and blue marks nor do I give blood up . When the nurses need to fill a tube or two for tests, it is hard to get enough flow to fill both the viles at time. Lots of times it clots before the tube is filled and they have to stick me  at another spot.  This begs the question is this 'thick blood', lack of blood flow tied to the Autism Pain Tolerance. I never even bleed when the right side pic line came out. It seems everyone else bleeds like a stuck pig and they are expetcing to hold the wound shut for 5 minutes or so.   Is this indeed a clue to the pain tolerance?