right|frame|a range of vacutainer tubes containing blood. a vacutainer blood collection tube is a sterile glass or plastic tube with a closure that is evacuated to create a vacuum inside the tube facilitating the draw of a predetermined volume of liquid. most commonly used to draw a blood sample directly from the vein, these also are used to collect urine samples. vacutainer tubes may contain additives designed to stabilize and preserve the specimen prior to analytical testing. tubes are available with or without a safety-engineered closure, with a variety of labeling options and closure colors as well as a range of draw volumes. vacutainer tubes, invented by joe kleiner and bd (becton, dickinson and company) in 1949, are manufactured and sold by bd. vacutainer is a registered trademark of becton, dickinson and company. ==principles==  right|thumb|tiger top vacutainer filled with blood. the vein is first punctured with the hypodermic needle which is carried in a translucent plastic holder. the needle is double ended, the second shorter needle being shrouded for safety by the holder. when a vacutainer test tube is pushed down into the holder, its rubber cap is pierced by the second needle and the pressure difference between the blood volume and the vacuum in the tube forces blood through the needle and into the tube. the filled tube is then removed and another can be inserted and filled the same way. it is important to remove the tube before withdrawing the needle, as there may still be some suction left, causing pain upon withdrawal. the test tubes are covered with a color-coded plastic cap. they often include additives that mix with the blood when collected (see below), and the colour of the tube's plastic cap indicates which additives that tube contains. the plastic caps are opaque for tubes with a normal vacuum. translucent-topped tubes contain a weaker vacuum in the same sized tube, and will obtain less blood. the weaker suction makes them more suitable for smaller sized veins, because the standardised suction of the tubes may cause the veins of elderly people or those with delicate veins to collapse. in this case a syringe should be used instead. ==contents of tubes== the tubes may contain additional substances that preserve the blood for processing in the medical laboratory. using the wrong tube may therefore make the blood sample unusable. these substances are typically a thin film coating that is applied using an ultrasonic nozzle, a video of the process can be seen here: blood collection tube coating video. the substances may include anticoagulants (edta, sodium citrate, heparin) or a gel with intermediate density 
Blood Medical_equipment