is a substance that stops blood from clotting. A group of pharmaceuticals called anticoagulants can be used in vivo
as a medication for thrombotic disorders. Some chemical compounds are used in medical equipment, such as test tubes, blood transfusion
bags, and renal dialysis equipment.
Anticoagulants as medications
Anticoagulants are given to people to stop thrombosis (blood clotting inappropriately in the blood vessels. This is useful in preventing deep vein thrombosis, myocardial infarctions and strokes in those who are predisposed.
The oral anticoagulants is a class of pharmaceuticals that act by antagonising the effects of vitamin K. The important is that they take at least 48 to 72 hours for the anticoagulant effect to develop fully. In cases when an immediate effect is required, heparin must be given concomitantly.
Generally these anticoagulants are used in prevention of embolisation - in
deep-vein thrombosis (DVT), pulmonary embolism, patients with atrial fibrillation and mechanical prosthetic heart valves.
The most important oral anticoagulants are :
Heparin and derivatives
is a biological substace, usually made from pig's intestines. It works by activating antithrombin III, which blocks thrombin from clotting blood.
Heparin can be used in vivo (by injection), and also in vitro to prevent blood or plasma clotting in medical devices. Vacutainers and test tubes containing heparin are usually coloured green.
Low-molecular weight heparin, is a more highly processed product that is useful as it...?
Anticoagulants outside the body
Laboratory instruments, test tubes, blood transfusion bags, and medical and surgical equipment will get clogged up and become unoperational if blood is allowed to clot.
Chemicals can be added to stop blood clotting. Apart from heparin, most of these chemicals work by binding calcium ions, preventing the coagulation proteins from using them.
- EDTA - denoted by mauve or purple caps on vacutainers and test tubes. This chemical strongly and irreversably binds calcium. It is in a powdered form.
- Citrate - this usually is in blue vacutainers. It is in liquid form in the tube and is used for coagulation tests, as well as in blood transfusion bags. It gets rid of the calcium, but no as strongly as EDTA. Correct proportion of this anticoagulant to blood is crucial because of the dilution.
- Oxalate - has a similar mechanism to citrate. It is the anticoagulant used in fluoride (grey top) tubes.