A needle assembly preferably suitable for single sample blood collection and for determining vein entry when collecting a blood sample from a patient into a vacuum collection device. This assembly includes a housing with an interior chamber with a blood inlet needle on one side of the housing and a blood outlet needle on the other. The outlet needle extends interiorly into the chamber, is closed at the end and includes a pair of holes each spaced preferably along an axial line. A slidable plug is operatively positioned in the chamber to prevent liquid from flowing into the side holes while allowing gas to flow into at least one of the side holes at a first position in the chamber whereby the prevented liquid may be viewed by a user through a transparent portion of the housing. The operative plug is movable to a second position in the chamber to allow liquid to flow into at least one of the side holes whereby liquid may be collected from the outlet needle of the assembly.