The measuring principle of the INR determining test system, is the same as the measuring principle of the instruments used in traditional clinical laboratory practice.
Namely that blood coagulation process is initiated in the tested sample by adding a reagent, and the optical change (change of turbidity). This optical change occurs as a result of the polymerisation of the fibrin, released by the thrombin and activated during the coagualtion process, and is detected by a measuring instrument (turbidimetry).
The change of turbidity as a function of time provides a coagulation curve, from which the measuring algorithm determines the coagulation time. On the basis of the coagulation time, with the parameters of the reagent, the device calculates the so-called INR value (International Normalized Ratio).