Medical syringes and saline ampoules (lower left). These are S-Monovette sample tubes, which combine a syringe with a sample tube for safe and rapid collection of blood from a patient. In an emergency, a sample of blood may be needed quickly to determine the blood group in case a transfusion is needed; or for analysis to aid diagnosis of an illness. The lids of the tubes are colour-coded according to different haematological tests or the content of the tube. Blue tubes, for example, are used for transfusion tests and they contain EDTA (ethylenediamine tetra-acetic acid), an anti- coagulant that prevent blood from clotting before the tests can be performed.