A needle assembly comprising: a housing (212, 312, 412, 512) defining a housing interior (220, 320); a cannula having a patient puncture tip extending from a first end of the housing (212, 312, 412, 512); a non-patient puncture tip (462, 562) extending from a second end of the housing (212, 312, 412, 512), the non-patient puncture tip and the patient puncture tip being in fluid communication with each other through the cannula, wherein the sole communication path between the housing interior and the external environment is via the patient puncture tip; and a porous vent (910, 910a) positioned within the housing interior to separate the housing interior into a first chamber and a second chamber, the porous vent (910, 910a) positioned within the housing interior to define the first chamber as having a volume of about 5 percent to about 20 percent of the total overall volume of the housing, with the cannula being in fluid communication with the first chamber, the porous vent (910, 910a) including pores for passage of blood at least partially into the porous vent (910, 910a), wherein the porous vent, the first chamber, and the second chamber are configured such that upon insertion of the patient needle tip into a patient blood flows through said cannula and into the first chamber and into contact with the porous vent without sealing the porous vent (910, 910a), and upon application of an evacuated container to said non-patient puncture tip, blood is drawn from said first chamber and air is drawn from said second chamber, thereby establishing a negative pressure within said second chamber with respect to an external environment of the needle assembly, and wherein at least a portion of the housing (212, 312, 412, 512) forming said first chamber is formed from a transparent or translucent material. a housing (212, 312, 412, 512) defining a housing interior (220, 320); a cannula having a patient puncture tip extending from a first end of the housing (212, 312, 412, 512); a non-patient puncture tip (462, 562) extending from a second end of the housing (212, 312, 412, 512), the non-patient puncture tip and the patient puncture tip being in fluid communication with each other through the cannula, wherein the sole communication path between the housing interior and the external environment is via the patient puncture tip; and a porous vent (910, 910a) positioned within the housing interior to separate the housing interior into a first chamber and a second chamber, the porous vent (910, 910a) positioned within the housing interior to define the first chamber as having a volume of about 5 percent to about 20 percent of the total overall volume of the housing, with the cannula being in fluid communication with the first chamber, the porous vent (910, 910a) including pores for passage of blood at least partially into the porous vent (910, 910a), wherein the porous vent, the first chamber, and the second chamber are configured such that upon insertion of the patient needle tip into a patient blood flows through said cannula and into the first chamber and into contact with the porous vent without sealing the porous vent (910, 910a), and upon application of an evacuated container to said non-patient puncture tip, blood is drawn from said first chamber and air is drawn from said second chamber, thereby establishing a negative pressure within said second chamber with respect to an external environment of the needle assembly, and wherein at least a portion of the housing (212, 312, 412, 512) forming said first chamber is formed from a transparent or translucent material.