Prothrombin time

The International Normalized Ratio (INR ) is a medical laboratory parameters of the function performance of the extrinsic pathway of blood coagulation. The INR is measured by the prothrombin time (PT; prothrombin time english, PT ) was determined. INR is a standardization of the Quick value.

Normal is an INR close to 1 An elevated INR value ( without taking anticoagulant medications ) may be caused for example by vitamin K deficiency, or severe liver disease. Does blood clotting for therapeutic reasons can be reduced so the INR target range is determined on a risk basis. Also note that the higher the INR, the higher the inhibition of coagulation and thus the embolic protection. At the same time the risk of bleeding (eg, bleeding from the gastrointestinal tract ) is increased at higher INR. In most cases (eg thrombosis, pulmonary embolism, atrial fibrillation) is the target area 2 to 3 In mechanical heart valves, however, the target area is higher, depending on the risk profile between 2.5 and 3.5. In high-risk profile, in rare cases, even with a target range of up to 4.5.

The measurement of the INR is especially important if the clotting time is prolonged medication with coumarin derivatives as oral anticoagulation. In a training course to learn the so- treated patients to determine their INR value themselves and to vary the dose of medication without the help of the doctor when necessary ( coagulation self-management ).

Calculation formula of the prothrombin time PT:

Where " test" is the prothrombin time of the sample to be tested, "normal " is the standard value and the ISI International Sensitivity Index. This is defined for each manufacturer or any prothrombinase as compared to an internationally standardized sample (typically between 1.0 and 1.4 ).