I have very visible flat blue veins in running from the underside of my top left arm to the bottom,they seem more visible than ever before.concerned?

Not necessarily: Pathological superficial arm veins are not usually flat but are distended and Don't collapse when elevating the arm above the shoulder. However if the vein pattern is noticeably different in the left arm in comparison to the right arm, consult your physician or a vascular surgeon for evaluation.

Should not be: concerned unless you have symptoms of venous occlusion farther down the arm. Increased varicose or large caliber veins usually mean venous insufficiency, or poor venous circulation, away from the heart. Unless you have been muscle building, which also increases venous return and therefore superficial vein size, you need to pay attention to symptoms of venous clot.