Blood sample bottles. Gloved hand holding an assortment of vacutainer blood sample bottles. The colour of the bottle top signifies the test that blood collected in the tube is to undergo. The bottle with the purple cap is used to collect samples for full blood counts and other general testing using EDTA (ethylenediamine tetra-acetic acid). The orange bottle contains serum separation gel for most clinical biochemical investigations. The bottle with the green cap has heparin in order to carry out specialised blood investigations. The blue topped bottle contains sodium citrate used in studies on blood coagulation.