Usefulness and accuracy of the international normalized ratio and activity percent of prothrombin time in patients with liver disease

Abstract

In order to determine the most reliable reporting style for prothrombin time (PT) in patients with liver disease, we examined the correlations between the plasma antigen levels of clotting factors and the PT activity percent or two international normalized ratios (INR), and compared the inter-reagent variation among these PT reporting styles. The PT was measured in 81 patients with liver diseases, including acute liver failure (ALF) (n = 10), acute liver injury (n = 52), chronic hepatitis (n = 8) and liver cirrhosis (n = 11), and in 75 warfarin-treated patients and 32 healthy volunteers. The PT of each plasma sample was determined with four commercial thromboplastins using an automated photo-optical coagulometer. For individual thromboplastin reagents, a locally determined international sensitivity index (local ISI) was derived using plasma obtained from healthy volunteers, warfarin-treated patients and liver disease patients. The INRW and INRLD were calculated using the corresponding local ISI. The PT activity percent was calibrated according to the Lineweaver-Burk equation. The PT values were compared with the plasma antigen levels of clotting factors X, II and VII measured using the enzyme-linked immunoassay method. The plasma factor X level was selected as the gold standard for measuring the synthetic liver function among the three clotting factors due to its significant relationship (P = 0.007) with the prognosis of ALF. The INRLD exhibited the closest correlation to the factor X level (r = 0.723-0.759), with the smallest inter-reagent variation among these reporting styles. The INRLD is the most appropriate PT reporting style for use in patients with liver disease.