Editing Prothrombin time (section)

===Factors determining accuracy===
[[Lupus anticoagulant]], a circulating inhibitor predisposing for thrombosis, may skew PT results, depending on the assay used.<ref>{{cite journal |vauthors=Della Valle P, Crippa L, Garlando AM, etal |title=Interference of lupus anticoagulants in prothrombin time assays: implications for selection of adequate methods to optimize the management of thrombosis in the antiphospholipid-antibody syndrome |journal=Haematologica |volume=84 |issue=12 |pages=1065–74 |date=December 1999 |pmid=10586206 |url=https://www.haematologica.org/cgi/reprint/84/12/1065 |format=PDF |access-date=7 February 2022 |archive-date=2 October 2011 |archive-url=https://web.archive.org/web/20111002154117/http://www.haematologica.org/cgi/reprint/84/12/1065 |url-status=dead }}</ref> Variations between various thromboplastin preparations have in the past led to decreased accuracy of INR readings, and a 2005 study suggested that despite international calibration efforts (by INR) there were still statistically significant differences between various kits,<ref>{{cite journal |vauthors=Horsti J, Uppa H, Vilpo JA |title=Poor agreement among prothrombin time international normalized ratio methods: comparison of seven commercial reagents |journal=Clin. Chem. |volume=51 |issue=3 |pages=553–60 |date=March 2005 |pmid=15665046 |doi=10.1373/clinchem.2004.043836 |doi-access=free }}</ref> casting doubt on the long-term tenability of PT/INR as a measure for anticoagulant therapy.<ref name=Jackson>{{cite journal |vauthors=Jackson CM, Esnouf MP |title=Has the time arrived to replace the quick prothrombin time test for monitoring oral anticoagulant therapy? |journal=Clin. Chem. |volume=51 |issue=3 |pages=483–5 |date=March 2005 |pmid=15738512 |doi=10.1373/clinchem.2004.045393 |doi-access=free }}</ref> Indeed, a new prothrombin time variant, the Fiix prothrombin time, intended solely for monitoring warfarin and other vitamin K antagonists has been invented<ref>Gudmundsdottir BR, Francis CW, Bjornsdottir AM, Nellbring M, Onundarson PT.
Thromb Res. 2012 Oct;130(4):674-81. doi: 10.1016/j.thromres.2011.12.013. Epub 2012 Jan 4.PMID 22225856</ref> and recently become available as a manufactured test. The Fiix prothrombin time is only affected by reductions in factor II and/or factor X and this stabilizes the anticoagulant effect and appears to improve clinical outcome according to an investigator initiated randomized blinded clinical trial, The Fiix-trial.<ref>Onundarson PT, Francis CW, Indridason OS, Arnar DO, Bjornsson ES, Magnusson MK, Juliusson SJ, Jensdottir HM, Vidarsson B, Gunnarsson PS, Lund SH, Gudmundsdottir BR.
Lancet Haematol. 2015 Jun;2(6):e231-40. doi: 10.1016/S2352-3026(15)00073-3. Epub 2015 May 25.
PMID 26688233 Clinical Trial.</ref> In this trial thromboembolism was reduced by 50% during long-term treatment and despite that bleeding was not increased.