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International Journal of Laboratory... Feb 2021The prothrombin time (PT) represents the most commonly used coagulation test in clinical laboratories. The PT is mathematically converted to the international normalized... (Review)
Review
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.
Topics: Humans; International Normalized Ratio; Prothrombin Time; Reference Standards
PubMed: 32979036
DOI: 10.1111/ijlh.13349 -
The American Journal of Medical... 1954
Topics: Prothrombin Time
PubMed: 13148187
DOI: No ID Found -
American Journal of Hematology Oct 2004The anticoagulant activity of warfarin sodium is monitored by the prothrombin time (PT) using the international normalized ratio (INR). Standard oral anticoagulant... (Review)
Review
The anticoagulant activity of warfarin sodium is monitored by the prothrombin time (PT) using the international normalized ratio (INR). Standard oral anticoagulant therapy monitoring requires frequent patient visits to physicians' offices and/or laboratories to optimize warfarin dosage. Home PT monitoring by patients can increase testing frequency and may thus decrease complications associated with oral anticoagulant therapy. Clinical studies suggest that home PT monitoring is more effective than uncoordinated management and is as effective as care through specialized anticoagulation clinics for keeping INRs within a therapeutic range. There are accurate and reliable instruments available, but paramount to the success of home PT monitoring is sound patient selection, appropriate patient training, and consistent quality control.
Topics: Anticoagulants; Drug Monitoring; Humans; International Normalized Ratio; Patient Education as Topic; Prothrombin Time; Self Care; Warfarin
PubMed: 15389909
DOI: 10.1002/ajh.20161 -
Clinics in Laboratory Medicine Jun 2009Prothrombin times and activated partial thromboplastin times have long been used as tests of overall ("global") clotting function. Laboratory coagulation testing issues... (Review)
Review
Prothrombin times and activated partial thromboplastin times have long been used as tests of overall ("global") clotting function. Laboratory coagulation testing issues should be at the forefront of the reader's consciousness whenever critically evaluating and extrapolating published study conclusions reliant on the results of these tests. Thus, this article reviews laboratory issues and known variables influencing prothrombin time and partial thromboplastin time results and international normalized ratio determinations.
Topics: Factor VIII; Humans; International Normalized Ratio; Partial Thromboplastin Time; Prothrombin Time
PubMed: 19665677
DOI: 10.1016/j.cll.2009.05.002 -
American Journal of Clinical Pathology Mar 1971
Topics: Animals; Brain Chemistry; Histological Techniques; Humans; Prothrombin Time; Rabbits
PubMed: 4927476
DOI: 10.1093/ajcp/55.3.385 -
American Journal of Clinical Pathology Oct 1970
Topics: Anticoagulants; Blood Coagulation Disorders; Humans; Indicators and Reagents; Plasma; Prothrombin Time; Thromboplastin
PubMed: 5471236
DOI: 10.1093/ajcp/54.4.670 -
Current Opinion in Hematology May 2004The increasing numbers of patients on oral anticoagulants may challenge the traditional organization of patient monitoring. The availability of portable coagulometers... (Review)
Review
PURPOSE OF REVIEW
The increasing numbers of patients on oral anticoagulants may challenge the traditional organization of patient monitoring. The availability of portable coagulometers capable of measuring prothrombin time (PT) international normalized ratio (INR) in a drop of capillary blood facilitates decentralization of monitoring by self-testing. This article reviews the literature on use of portable coagulometers.
RECENT FINDINGS
Numerous studies have evaluated the reliability of portable coagulometers in testing the PT-INR. This has been assessed by statistically as well as clinically relevant criteria. Other studies have been devoted to developing calibration models fulfilling the criteria recommended by the World Health Organization (WHO) for the calibration of INR measuring systems. Finally, studies have assessed the value of schemes for patient training and for the long-term quality assurance of portable coagulometers.
SUMMARY
It can be concluded from the published studies that PT-INR self-testing may be considered as a suitable alternative to conventional laboratory testing. For the PT-INR to be reliable, manufacturers of portable coagulometers should calibrate their devices against international standards for thromboplastin with procedures similar to those recommended by WHO for conventional measuring systems. Training of patients and implementation of appropriate quality assessment schemes are also essential prerequisites for the success of PT-INR self-testing.
Topics: Administration, Oral; Anticoagulants; Humans; International Normalized Ratio; Patient Education as Topic; Prothrombin Time; Quality Assurance, Health Care; Reproducibility of Results; Self Care
PubMed: 15257011
DOI: 10.1097/01.moh.0000130311.10539.b5 -
Nihon Rinsho. Japanese Journal of... Sep 1999
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Surgery Nov 1995
Topics: Blood Coagulation; Humans; Prothrombin Time
PubMed: 7482283
DOI: 10.1016/s0039-6060(05)80286-7 -
Data mining for prothrombin time and international normalized ratio reference intervals in children.PloS One 2022Reference intervals (RIs) help physicians in differentiating healthy from sick individuals. The prothrombin time (PT) and International normalized ratio (INR) fluctuate...
Reference intervals (RIs) help physicians in differentiating healthy from sick individuals. The prothrombin time (PT) and International normalized ratio (INR) fluctuate in coagulation pathway defects and have interlaboratory variability due to the instrument/reagent used. As direct method is difficult in children, we chose an indirect data mining method for the determining PT/INR RIs. The indirect method overcomes the substantial financial and logistic challenges, and ethical restrictions in children, moreover, allows partitioning in more fine-grained age groups. Prothrombin Time/INR measurements performed in patients aged birth-18 years between January 2013 and December 2020, were retrieved from laboratory management system of the Aga Khan Hospital. Reference intervals were computed using an indirect KOSMIC algorithm. The KOSMIC package function on the assumption that the non-pathologic samples follow a Gaussian distribution (after Box-Cox transformation of the data), following an elaborate statistical process to isolate distribution of physiological samples from mixed dataset. A total of 56,712 and 52,245 values were retrieved for PT and INR respectively. After the exclusion of patients with multiple specimens obtained during the study period, RIs were calculated for 37,356 (PT) and 37,192 (INR) children with stratification into 9 age groups. A comparison of 2.5th and 97.5th percentile results with those of established RIs from SickKids Handbook of Pediatric Thrombosis and Hemostasis demonstrated good agreement in between different age groups. This study supports data mining as an alternate approach for establishing PT/INR RIs, specifically in resource-limited settings. The results obtained are specific to studied population and instrument/reagent used. The study also allows understanding of fluctuations in coagulation pathways with increasing age and hence better clinical decision-making based on PT and INR results.
Topics: Humans; Child; Aged; Prothrombin Time; International Normalized Ratio; Blood Coagulation Tests; Reference Values; Indicators and Reagents; Data Mining
PubMed: 36302050
DOI: 10.1371/journal.pone.0276884