I've had a couple of blood tests now at my local health centre and not once has the nurse sterilised the area or cleaned her hands before performing the test, despite needing to touch the area with her (ungloved) fingers.

Everytime I've asked them to sterilise the area and clean their hands with alcohol gel and everytime I've gotten the same response:  we don't do that because the presence of alcohol on the skin can corrupt the results of the blood test. 

Is this true?  If so, why then do they always sterilise the area and their hands with alcohol first in hospitals?