Is it dangerous to have vein collapse during blood work? what could it be from? could it be a vascular problem?

Reflex: A vein that has been punctured or even approached with a needle may have its smooth muscle contract, narrowing the lumen and sending the available blood elsewhere. Nobody knows why it happens to some veins on some people on some days, and not others. Don't worry about it -- it happens all the time.

No: Vasospasm (vein shrinking) during blood work is commonly seen and not dangerous. It is the result of anxiety, anticipation of the potential pain with the needle stick, which activates the sympathetic nervous system resulting in vasospasm. It does not imply vascular problem.