Effect of thromboplastin and coagulometer interaction on the precision of the International Normalised Ratio.

• DOI: 10.1136/jcp.48.1.13
• Publication Date: 2007-06-09T00:50:46Z
• Authors: D W Pi; J M Raboud; C Filby; C J Carter
• Keywords: Prothrombin time; Coefficient of variation; Thromboplastin

AIMS--To examine the magnitude of thromboplastin and coagulometer interactions on precision International Normalised Ratio (INR) values when manufacturers9 recommended instrument specific Sensitivity Index (ISI) are adopted for INR calculation. METHODS--The variability obtained from four automated phototopical coagulometers frequently used in North American laboratories was studied. When with five commercial thromboplastins moderate to high sensitivity (ISI 0.92-1.97), 20 prothrombin time results were generated each a population 98 patients established warfarin treatment. RESULTS--The mean ranged 2.05 2.81, depending which reagent/coagulometer combination used. Within patient variation increased as median value increased. The coefficient within 10%; seconds ratio 21 18%, respectively. CONCLUSIONS--There considerable bias estimated ISI compared value. Despite this apparent imperfection, our study clearly showed that is preferable other reporting formats assessing degree anticoagulation