<prompt> True regarding prothrombin time measurement? -Platelet rich plasma is requiredActivate with kaolinShould be measured within 2 hoursImmediate refrigenation to preserve coagulation factor bility  <response>: Normal prothrombin time is 10-14 seconds So, from the given options prothrombin time should be measured within 2 hours is selected The prothrombin time PT - along with its derived measures of prothrombin ratio PR and international normalized ratio INR - are assays evaluating the extrinsic pathway and common pathway of coagulation. This blood test is also called protime INRand PTINR. They are used to determine the clotting tendency of blood, in the measure of warfarindosage, liver damage, and vitamin K status. PT measures the following coagulation factors: I fibrinogen, II prothrombin, V proaccelerin, VII proconvein, and X Stua-Prower factor. The reference range for prothrombin time depends on the analytical method used, but is usually around 12-13 seconds results should always be interpreted using the reference range from the laboratory that performed the test, and the INR in absence of anticoagulation therapy is 0.8-1.2. The target range for INR in anticoagulant use e.g. warfarin is 2 to 3. In some cases, if more intense anticoagulation is thought to be required, the target range may be as high as 2.5-3.5 depending on the indication for anticoagulation. Ref Robbins 9e pg 450 