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INR derivation with the PT/INR Line simplified using a spreadsheet from the world wide web
  1. Leon Poller1,
  2. Saied Ibrahim1,
  3. Albert Pattison2,
  4. Jørgen Jespersen3,4,
  5. European Action on Anticoagulation (EAA), formerly European Concerted Action on Anticoagulation (ECAA)
  1. 1EAA Central Facility, Faculty of Life Sciences, University of Manchester, Manchester, UK
  2. 2Hart Biologicals, Hartlepool, UK
  3. 3Department of Clinical Biochemistry, Hospital of South West Denmark, Denmark
  4. 4Department for Thrombosis Research, University of Southern Denmark, Esbjerg, Denmark
  1. Correspondence to Professor Leon Poller, EAA (ECAA) Central Facility, Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, UK; leon.poller{at}


Background The prothrombin time/international normalised ratio (PT/INR) Line method to derive INR, based on only five European Concerted Action on Anticoagulation (ECAA) certified plasmas, is shown to be reliable in previous ECAA studies. A simpler method not requiring linear regression calculation would be an advantage.

Method After determining the local PT/INR Line, local INRs have been obtained using a readily available spreadsheet on the internet which laboratories can use without performing any additional calculations.

Results Examples of INR derivation have been obtained from results at 16 centres using a range of local coagulometers with human thromboplastin international reference preparations (IRPs). The procedure does not require manual PT testing, local international sensitivity index calibration, availability of thromboplastin IRPs or local mean normal prothrombin time.

Conclusions From the PT/INR Line, INR values for local PT results are easily obtained using an Excel spreadsheet from our website ( which does not require the complex linear regression analysis to derive INR.

  • INR
  • prothrombin time
  • PT/INR Line
  • ECAA plasmas
  • polycythaemia
  • erythrocyte
  • haematology
  • myeloproliferative disease
  • anticoagulants
  • computer assisted
  • quality assurance
  • safety
  • colorectal cancer
  • gall bladder
  • oncogenes
  • p53/attribute
  • pancreas
  • leukaemia
  • polycythaemia

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  • Funding The work was supported by the Manchester Thrombosis Research Foundation, a UK registered charity.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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