Heparin tubes are used in clinical biochemistry.
The tube is coated with the anti-coagulant Lithium-Heparin.
Heparin activates antithrombin, i.e. blocking the coagulation cascade.
The Lithium Heparin in BD Vacutainer tubes is spray dried onto the inner walls to achieve the best possible solubility. For clinical chemistry, lithium heparin is generally preferred over sodium heparin.
To avoid micro-clotting, mix the Heparin tube with 8-10 inversions immediately after the blood sample has been taken.