I change my pins to draw/inject but it's not necessary.
I've done it without and there is no noticeable difference. If you're doing proper injection technique changing the pin really isn't necessary other than maybe offering some peace of mind.
how many times have you been to your physician and they changed out needles after drawing before giving you an injection?
My dr / RN always changes the pin. Many times they will walk in with a pre loaded pin so you can't see if they switched them - but they told me they switch them. I have also seen them do it right in front of me. Always change out the pin. My RN that gives my injections says they are taught to change the needles in their training.
at the end of the day it is really just a matter of pain. Pins are so cheap why not switch them and make injecting as pleasant as possible?
Even if I have to use the same sizes pin to pull as I do to inject, I change that sucker out. Sterility is my reason. Even thought I wipe my vials with alcohol, etc., that sucker goes deep down in ya, so I'd like to know the whole thing is clean.