Blood collection tubes are widely used, because in clinical laboratories and other professional diagnostic test settings, serum and plasma specimens have to be prepared, instead of using the whole blood directly. Based on the purpose and the requirement of the in-vitro diagnostic tests, different vacuum tubes are needed, such as gel and clot tubes, Clot Activator tubes, K3EDTA tubes, Sodium heparin tubes, Sodium citrate tubes.
A 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. The 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.
The test tubes are covered with a color-coded plastic cap. They often include additives that mix with the blood when collected 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.