High prothrombin time is caused by blood-thinning drugs such as warfarin, a lack or limited level of blood clotting factors and inhibitor substances. Alteration in the activity of one or more clotting factors and increased use of clotting factors also increase prothrombin time.
Prothrombin time refers to a blood test that measures the amount of time taken for blood to clot. This test is used in checking for bleeding problems and to verify if drugs to prevent blood clots are working.
There are two ways of presenting prothrombin time: prothrombin time in seconds and prothrombin time as a ratio. Prothrombin time in seconds involves measuring the time it takes for blood to clot in seconds. However, the results from this method may vary based on the laboratory and the blood testing method. On average, blood takes 10 to 14 seconds to clot.
Blood may take too long to clot due to liver problems, vitamin K deficiency and insufficient protein levels. Blood may also clot too fast due to vitamin K supplements, estrogen-containing drugs and high intake of foods containing vitamin K.
Prothrombin time as a ratio is often used with people on blood-thinning medication. Results of this procedure are given in a ratio referred to as international normalized ratio, a formula that takes care of the differences due to chemical use.