According to CLSI "Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture; Approved Standard - Sixth Edition" H3-A6 on page 15 it states: Anchoring the vein from above is not recommended due to the risk of an accidental needlestick.
Common sense also dictates that you do not put your fingers above the needle. A patient suddenly jumps and in a split second you have potentially been exposed to a life-changing blood-born pathogen.
Catherine Ernst, RN, PBT (ASCP)
Center for Phlebotomy Education, Inc.