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Prothrombin time (PT)

Screening test of the extrinsic plasmatic coagulation cascade, in particular factor I, II, V, VII und X. In addition, therapy with warfarin and phenprocoumon can be monitored with PT. For better comparability of different laboratories, the prothrombin time is given as an international normalized ratio (INR).

Standard value:

INR 0,9--1,25.

Laboratory test method:

Ball coagulometer.

Indications:

Screening test for coagulation disorders, treatment with warfarin or phenprocoumon, evaluation of liver function.

Differential Diagnosis of Prolonged PT

• Acquired or congenital deficiency of coagulation factors I, II, V, VII and X.
• Liver insufficiency.
• Therapy with direct oral anticoagulants (DOAK), warfarin or phenprocoumon. A typical target INR for people on warfarin therapy would be 2.0--3.0 in case of low-risk atrial fibrillation and 3.0--4.5 for people with a higher risk (mechanical heart valve, after recurrent embolism).

Differential Diagnosis of shortened PTT

Activation of the coagulation system due to traumatic venipuncture or acute-phase-response.

References

  Deutsche Version: Gerinnungstest PTT