A high prothrombin time is a prolonged prothrombin time, which represents a decrease in fibrinogen activity or a decrease in the concentration of fibrinogen in the plasma being tested. This is because the prothrombin time is the time it takes to add prothrombin to the plasma and observe the appearance of clotting in the plasma. Thrombin is coagulation factor II, which turns fibrinogen into active fibrin monomers, and the fibrin monomers can then cross-link with each other to form a fibrin blood clot, which will form a precipitate visible to the naked eye. If the prothrombin time is prolonged, it means that the concentration or activity of fibrin in the plasma is decreased, which can be seen clinically in a variety of diseases, the most common being the decrease in fibrin concentration caused by various liver diseases, such as cirrhosis and severe hepatitis, which eventually cause the prolongation of the prothrombin time due to the decreased ability of the liver to produce fibrinogen.