Is it necessary to wipe finger with an antiseptic pad before pricking it for a blood sample for a glucometer?

I can't find the manual of my glucometer, but normally when I take a blood sample from my finger I don't wipe it first with an antiseptic pad. Am I tainting the result of the blood with contaminants it may touch on the surface of my finger, and am I risking an infection by not cleaning area first?