Prothrombin time/INR (VKA monitoring)
Patient plasma is incubated with thromboplastin reagent, which contains recombinant tissue factor, synthetic phospholipids & calcium ions. FVIIa forms a complex with tissue factor in a phospholipid and calcium dependent manner to autoactivate FVII and then FX to FXa to begin the 'common' pathway which generates thrombin via the prothrombinase complex to form a fibrin clot. The process of timing to clot formation begins upon the addition of calcium ion-containing thromboplastin to replace those removed by the tri-sodium citrate anticoagulant and thereby facilitate functioning tenase and prothrombinase complexes.
Conversion of prothrombin time results to international normalised ratio (INR) exists to standardise VKA monitoring between alternative reagents and analytical platforms as far as is possible. Our laboratories undertake local international sensitivity index (ISI) calibration of thromboplastin reagents to maximise INR accuracy.
Therapeutic range: 2.0 - 4.0
500µL x 1 aliquot
Internal requests: please refer to EPR label
The sample should be analysed within 4 hours of venepuncture. Please ensure sample tubes are filled exactly to the fill-line as underfilling creates a dilution error and leads to inaccurate results.
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH
Laboratory opening times
Last updated: 09/03/2017