LOW INTERINSTRUMENT VARIABILITY OF THE INTERNATIONAL NORMALIZED RATIOWITH THE COAGAMATE X2 SIMPLASTIN EXCEL SYSTEM

Minimizing the interlaboratory variability of the International Normal ized Ratio (WR) for patients receiving coumarin therapy will require l ocal laboratory calibration of individual coagulation instrument/reage nt systems. However, some laboratories possess multiple coagulation in struments of the same model, and it is unclear if each instrument woul d require separate calibration. To address this question, a controlled study was performed that examined the interinstrument variability of the INR on three separate Coagamate X2 coagulometers (Organon Teknika Durham, NC) using the Simplastin Excel reagent (Organon Teknika) (Inte rnational Sensitivity Index = 2.14). The interinstrument coefficient o f variation (CV) of the INR among the three instruments was 3.4% and 3 .5% for patient control plasmas (n = 20) and coumarin plasmas (n = 40, INR range 1.5-4.6), respectively. The number of discordant INRs betwe en paired instruments (one INR within and one INR out of the therapeut ic range, plus a difference of at least 0.4 INR units) was very tow (0 %). The interinstrument INR CVs for three commercial quality control p lasmas were 2.6% (INR = 0.92), 4.1% (INR = 2.1), and 6.3% (INR = 4.5), and correlated well with the low CVs for patient samples. This study showed that the Coagamate X2/Simplastin Excel system is capable of ver y low interinstrument INR variability, and surpasses the interlaborato ry CVs reported in the literature, Formal calibration of a single inst rument may be adequate for laboratories possessing multiple instrument s of the same model.