What is the angle that venipuncture is performed?

Varies: There is no set rule on the angle of entry. For smaller veins close to the skin, the angle is more acute with the needle/catheter closer to the skin. Deeper veins may require 45 degree angle, and larger angles make for more difficult entry as the tip may easily penetrate the back wall of the vein.

Smaller the better: As dr isobe said, the angle of venipuncture varies. Deeper veins may require a larger degree angle, but most venipuncture is on smaller superficial veins in the skin and the smaller the degree of the angle, the closer to parallel, the better.There is less chance for going through the vein, less bruising, less chance of failure to draw the blood.