What are possible reasons for blood draws with lower than expected blood volume?

Possible reasons for blood draws with lower than expected blood volume include: 1) The phlebotomist has not waited enough time for the blood to stop flowing into the tube. 2) The tube has "pushed back" from the needle end attached to the holder and the tube is no longer drawing. 3) Discard tube was not used. For further information see the video Collecting Specimens In PAXgene Blood RNA Tubes and Instructions for Use.