Blood collection and storage is done is special tubes which allow the preservation of the blood sample over long periods. These tubes can be made of glass or plastic and the caps of these vials are coloured to indicate the additives in them. Some of the additives are anticoagulants such as EDTA, sodium citrate or heparin. Other substances include preservatives. The containers containing coagulants are capped with gold, red or orange caps. The ones containing anti-coagulants are green, which contain heparin, purple or lavender indicates ones which contain EDTA, grey capped tubes contain sodium fluoride or oxalate. Blood collection tubes (also called as vacutainers) are extensively used in hospitals, medical centres and diagnostic centres. In biological labs, it is used in experiments like haemolysis etc.