In newborns, a capillary whole blood specimen is used.

The blood is mixed, then centrifuged to separate blood cells from plasma (as prothrombin time is most commonly measured using blood plasma).

Blood is drawn into a test tube containing liquid sodium citrate, which acts as an anticoagulant by binding the calcium in a sample.

Prothrombin time is typically analyzed by a laboratory technologist on an automated instrument at 37 ☌ (as a nominal approximation of normal human body temperature). Methodology Vacutainer tube used for PT and PTT blood tests 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. The target range for INR in anticoagulant use (e.g. 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. PT is often used in conjunction with the activated partial thromboplastin time (aPTT) which measures the intrinsic pathway and common pathway of coagulation. PT measures the following coagulation factors: I (fibrinogen), II (prothrombin), V (proaccelerin), VII (proconvertin), and X (Stuart–Prower factor).

They are used to determine the clotting tendency of blood, in such things as the measure of warfarin dosage, liver damage, and vitamin K status. This blood test is also called protime INR and PT/INR. The prothrombin time ( PT) – along with its derived measures of prothrombin ratio ( PR) and international normalized ratio ( INR) – is an assay for evaluating the extrinsic pathway and common pathway of coagulation.

Inr normal range chart