Anti-coagulant medications that delay the formation of blood clots are administered to prevent thrombosis and embolism in many medical disorders. For patients with these conditions, the time that their blood takes to clot needs to be monitored regularly so that the drug dosage can be optimised. The Profhrombin Time/Intemational Normalised Ratio (MR) test works by introducing a biochemical substance called fhromboplastin to a blood sample that starts the same series of clotting reactions that occur when a blood vessel is ruptured in the body. The clot changes the blood from a free-flowing solution to a gel-like substance with a markedly different viscosity - and the time it takes this change in viscosity to occur is then measured.
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