What is the Prothrombin Index
after the American doctor Armand J. Quick
Synonyms: Quick-Zeit, Quick, Quicktest, Prothrombin Ratio (PR), Thromboplastinzeit, TPZ, Prothrombinzeit, PTZ, Normotest®
English: prothrombin time
The Quick value is a laboratory parameter from coagulation diagnostics, which is used to record disorders of blood coagulation (hemostasis).
An alternative representation of the same measurement result is the prothrombin time in seconds. However, this is practically not used in Germany.
The Quick value is used to measure the thrombin formation after activation with tissue thromboplastin, i.e. the extrinsic (exogenous) part of the coagulation system is checked. The result is given in percent, with 100% being the mean value of a normal population. The Quick value primarily checks the coagulation factors prothrombin (II), V, VII and X.
The Quick value may be reduced in patients taking direct oral anticoagulants. The effect is more pronounced with factor Xa inhibitors than with thrombin inhibitors.
The Quick value is a basic parameter in coagulation diagnostics and is used as a search test to rule out coagulation disorders, e.g. preoperatively. In addition, the Quick value is used for regular therapy control in patients on anticoagulation with coumarin derivatives.
Since most of the coagulation factors are produced in the liver, the Quick value is a good parameter for the course of liver synthesis disorders. The Quick value makes little contribution to the diagnosis of congenital coagulation disorders - a factor VII deficiency is e.g. B. very rarely.
For the examination, 2-5 ml of citrated blood is drawn. Prefabricated extraction systems must be filled up to the mark. Long venous congestion and foam formation during collection should be avoided, the sample should be mixed immediately and centrifuged if necessary. The plasma should be analyzed within 5 hours.
The blood is centrifuged in the laboratory. The examination is carried out fully automatically with citrate plasma. The plasma is heated to 37 degrees and exactly as much calcium is added again as was previously inactivated by the citrate solution. The addition of tissue thromboplastin activates the extrinsic system of blood clotting. The time until a clot appears is measured mechanically or optically (clotting test) and compared to the clotting time of a normal plasma. A Quick value of 100% corresponds to the coagulation time of the normal plasma pool. A reference curve is created by diluting the normal plasma.
A Quick value of 50% indicates that the blood plasma of the sample examined coagulates at the same rate as a standard plasma that has been diluted in a ratio of 1: 2. A Quick value of 50 percent does not mean a doubling of the measured coagulation time.
Due to the differently sensitive reagents and measuring devices, the Quick values can vary from laboratory to laboratory (method-dependent). That is why the Quick value is converted into the standardized INR value (International Normalized Ratio). Quick and INR behave in opposite directions, a "low" Quick value corresponds to a "high" INR. The INR is calculated as follows:
- INR = (TPZ patient plasma [sec] / TPZ normal plasma pool [sec])ISI
The ISI (International Sensitivity Index) is a specific value for each thromboplastin and each thromboplastin batch. The INR plays a role primarily in monitoring therapy with vitamin K antagonists.
6 reference ranges
|Newborn||1st day of life||55-100%|
|5th day of life||58-100%|
|90th day of life||65-100%|
|children||6.-30. Month of life||53-100%|
|31st month-7th year of life||65-100%|
The Quick value is recorded Not the intrinsic coagulation system, which can be evaluated using the partial thromboplastin time (PTT). Patients with haemophilia therefore have a normal Quick value. The common end route of the extrinsic and intrinsic system, the conversion of fibrinogen to fibrin, can be recorded using the plasma thrombin time (PTZ).
Reasons for a reduced Quick value or an increased INR are:
8 disruptive factors
|Disruptive factor||Quick value|
|Preanalytics||long venous congestion||local activation of fibrinolysis → Quick decreased|
|strong aspiration when taking blood||Coagulation activation → Quick decreased|
|Incorrect citrate-plasma ratio (tubes incompletely filled)||Citrate excess → Quick decreased|
|too little centrifugation||Platelet rich plasma → Quick increased|
|Disruptive factors in the matrix||Hemolysis||Release of coagulation-activating substances → Quick reduced|
|lipemic blood samples||Quick humiliated|
|Acetylsalicylic acid||Quick humiliated|
|Heparin therapy||lower activity of the prothrombin complex (from approx. 0.3-2 U / ml plasma) → Quick decreased|
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