Editing Prothrombin time (section)

===Interpretation===
The prothrombin time is the time it takes [[blood plasma|plasma]] to clot after addition of [[tissue factor]] (obtained from animals such as rabbits, or recombinant tissue factor, or from brains of autopsy patients). This measures the quality of the ''extrinsic pathway'' (as well as the ''common pathway'') of [[coagulation]]. The speed of the ''extrinsic pathway'' is greatly affected by levels of functional [[factor VII]] in the body. Factor VII has a short [[half-life]] and the [[carboxylation]] of its [[glutamate]] residues requires [[vitamin K]]. The prothrombin time can be prolonged as a result of deficiencies in vitamin K, [[warfarin]] therapy, [[malabsorption]], or lack of intestinal colonization by bacteria (such as in [[newborn]]s). In addition, poor factor VII synthesis (due to [[liver disease]]) or increased consumption (in [[disseminated intravascular coagulation]]) may prolong the PT.{{citation needed|date=July 2020}}

The INR is typically used to monitor patients on warfarin or related oral anticoagulant therapy.  The normal range for a healthy person not using warfarin is 0.8–1.2, and for people on warfarin therapy an INR of 2.0–3.0 is usually targeted, although the target INR may be higher in particular situations, such as for those with a [[artificial heart valve|mechanical heart valve]]. If the INR is outside the target range, a high INR indicates a higher risk of bleeding, while a low INR suggests a higher risk of developing a clot. In patients on a vitamin K antagonist such as warfarin with supratherapeutic INR but INR less than 10 and no bleeding, it is enough to lower the dose or omit a dose, monitor the INR and resume the vitamin K antagonist at an adjusted lower dose when the target INR is reached.<ref name=Farinde2019>{{cite journal|url=https://emedicine.medscape.com/article/2172018-overview|title=Warfarin Overanticoagulation |website=Medscape|date=2019-04-18|author=Abimbola Farinde}}</ref> For people who need rapid reversal of the vitamin K antagonist – such as due to serious bleeding – or who need emergency surgery, the effects of warfarin can be reversed with vitamin K, [[prothrombin complex concentrate]] (PCC), or [[fresh frozen plasma]] (FFP).<ref name=Ag2012>{{cite journal | vauthors = Ageno W, Gallus AS, Wittkowsky A, Crowther M, Hylek EM, Palareti G | title = Oral anticoagulant therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines | journal = Chest | volume = 141 | issue = 2 Suppl | pages = e44S–e88S | date = February 2012 | pmid = 22315269 | pmc = 3278051 | doi = 10.1378/chest.11-2292 }}</ref>
{{further|Warfarin#Overdose}}