Standardization of Prothrombin Time/International Normalized Ratio (PT/INR)

Abstract

The prothrombin time (PT) represents the most commonly used coagulation test in clinical laboratories. The PT is mathematically converted to the international normalized ratio (INR) for use in monitoring anticoagulant therapy with vitamin K antagonists such as warfarin in order to provide test results that are adjusted for thromboplastin and instrument used. The INR is created using two major PT ‘correction factors’, namely the mean normal PT (MNPT) and the international sensitivity index (ISI). Manufacturers of reagents and coagulometers have made some efforts to harmonizing INRs, for example, by tailoring reagents to specific coagulometers and provide associated ISI values. Thus, two types of ISIs may be generated, with one being a ‘general’ or ‘generic’ ISI and others being reagent/coagulometer‐specific ISI values. Although these play a crucial role in improving INR results between laboratories, these laboratories reported INR values are known to still differ, even when laboratories use the same thromboplastin reagent and coagulometer. Moreover, ISI values for a specific thromboplastin can vary among different models of coagulometers from a manufacturer using the same method for clot identification. All these factors can be sources of error for INR reporting, which in turn can significantly affect patient management. In this narrative review, we provide some guidance to appropriate ISI verification/validation, which may help decrease the variability in cross laboratory reporting of INRs.

Updates on Anticoagulation and Laboratory Tools for Therapy Monitoring of Heparin, Vitamin K Antagonists and Direct Oral Anticoagulants

“…Heparin binds to antithrombin via its pentasaccharide, catalyzing the inactivation of thrombin and other clotting factors [ 1 ]. Warfarin, a vitamin K antagonist used to hamper γ-carboxylation of vitamin K-dependent coagulation factors, has also been used historically as an anticoagulant [ 1 , 2 ]. Drug monitoring in clinical laboratory tests is required when using these drugs.…”

Association Between Pre-delivery Coagulation Indicators and Invasive Placenta Accreta Spectrum

“…As PT reflects exogenous coagulation function, an increase in PT implies a hypocoagulability status in FIGO grade 3 compared with FIGO grade 2. 12 FDP and D-dimer are degradation products created by fibrinolytic enzymes acting on crosslinked fibrin, 13 and the increase in FDP and D-dimer levels might imply fibrinolytic hyperactivity in FIGO grade 3. The association identified by this study indicated hypocoagulability and hyperfibrinolysis status along with PAS deterioration.…”

Snakebite Associated Thrombotic Microangiopathy and Recommendations for Clinical Practice

“…VICC is characterised by procoagulant toxins activating various clotting factors, leading to activation of the coagulation cascade, factor consumption and a resultant consumption coagulopathy [4,7]. VICC presents with a reduced or unrecordable fibrinogen; prolonged or unrecordable PT (or its international normalised standardised equivalent, the international normalised ratio (INR) [33]) and activated partial thromboplastin time (APTT); and an elevated D-dimer [34]. It is an acute and transient coagulopathy associated with a risk of bleeding, worse in snake venoms that also contain metalloproteinases.…”