What gauge needle is used on the typical medical patient for a chemistry profile?

Depends how it is drawn- Butterfly or straight stick

19 g and 21 G are the normal straight stick. If you use a buterfly to draw the lab then they are ususally 21 or 23 Gauge. (Remember the bigger the gauge number the smaller the needle width). The smaller the needle width the higher the chance of hemolization (cell squishing)