Significance of local international sensitivity index systems for monitoring warfarin and liver function.

OBJECTIVES Use of a local calibrator has been recommended for standardization of the international normalized ratio (INR) and international sensitivity index (ISI). We investigated the performance of two commercial local calibrators for warfarin monitoring and determined the significance of liver-specific INR. METHODS ISI values were determined using the World Health Organization (WHO) method and two commercial local calibrators. Liver-specific ISI was determined using plasma samples from patients with liver cirrhosis and normal controls. RESULTS In warfarin monitoring, the two local ISIs determined by the two local calibrators showed better consistency than uncorrected ISI, although they were inferior to the ISIs calibrated using the WHO method. Alternative calibration using calibration plasma from patients with liver cirrhosis instead of warfarinized plasma reduced the INR variability. CONCLUSIONS Local ISI determined by a commercial local calibrator improved INR standardization among thromboplastins. The alternative ISI calibration using liver-specific calibration plasma is expected to reduce INR variability for the evaluation of liver function.