Hi KittyCat,

Aren't you a med tech in a previous life?  Or am I mistaken?  I am not a med
tech, but a veteran phlebotomist, lab and medical assistant.  I know that
hitting a surface pain receptor is what makes the difference between a
painful draw and one that cannot be felt at all.  Pushing through one of the
valves that are located in the vein might make for more pain, or impede the
collection of blood and necessitate a second draw.  Less experienced
phlebots often stick through the vein completely and out the back of it, and
this is most often what causes bruising around the site of the stick.

My understanding of "collapsing veins" as relates to blood drawing, is that
the suction in a vacuum tube is too much for the delicate vein in question.
The "collapse" of the vein is a very transient thing... the vein fills right
back up with the blood that is circulating around in the body.  I can tell
(by feel) a vein that is likely to collapse... and patients often volunteer
this information quite readily!  I most often used a syringe on a vein like
this... so that I can have direct control of the amount of suction on the
vein, so that it won't collapse.  But I notice at UCSF, where I have my
blood drawn, they always use butterfly needles now (as some kind of needle
stick precaution), and these also are easier on the delicate and smaller
veins.

The vein would not stay collapsed, and I have never heard of any kind of
pain reported because of the "collapability" of the vein.  Hitting a larger
nerve--ah!  One would know that right away.  Perhaps she has a vein valve
right at her antecubital, or a higher ratio of pain receptors there.

I have now exhausted my speculations, and I hope it helped, even a little
bit.

Be well,

Mair