The only way we know what is going on in the human body is by regular blood testing. If the hypodermic equipment is not sharp enough to pierce the skin multiple problems can occur.
Hypodermic needles sterile single use, for use with reusable glass syringe
Needle for prefilled and reusable pen injectors
Brands include BD Microfine, Novofine, Novotwist, Unifine, Pentips.
Brands include penfine
Lots of equipment out there to try to make regular testing as pain free as possible.
A good blood test by a health professional qualified to take blood should not leave marks, bruises or any muscle twitching. If problems occur ask for some other qualified to take bloods, done with a sharp syringe, relaxation and a reasonable time factor blood taking can be a pleasant experience with no problems.