of the thromboplastin reagent used. ISI is obtained from cali-Prothrombin time (PT) is a universal indicator of liver bration, using oral anticoagulated patient plasmas, of a given disease severity. However, variability in thromboplastin thromboplastin against the World Health Organization referreagents leads to large interlaboratory differences in PT ence thromboplastin, which is assigned an ISI of 1.0.
results. The aim of this study was to determine whether
The INR has been proposed also 2,9 and is now accepted the use of the international normalized ratio (INR) or routinely [10][11][12] to standardize PT reporting in liver failure. other modes of expression might achieve PT standard-However, the INR/ISI system has been meant and validated ization in patients with liver failure. PT was measured for monitoring oral anticoagulant therapy only 8,13 and its relwith seven thromboplastin reagents with different senevance in liver failure is hypothetical and is starting to be sitivities in plasmas from 27 patients with miscellaneous criticized. 14 chronic and acute liver failure and, as a control popula-
The aim of this study was to determine if the use of INR tion, 29 patients on oral anticoagulation therapy. PT was or other modes of expression might achieve PT standardizaexpressed in seconds, ratio, activity percentage, and tion in patients with liver failure.
INR. In patients with liver failure, only activity percentage expression eliminated variability in PT results ob-PATIENTS AND METHODS tained with the seven thromboplastins while INR, seconds, and ratio values remained significantly different
Plasma samples were obtained from 27 patients with miscellaneous chronic and acute liver failure and 29 oral anticoagulated pa-(P Γ΅ .01). In patients on oral anticoagulant therapy, only tients as a control population.
INR normalized PT results. We conclude that, in patients
PT was determined on freeze (080ΠC)-thawed (37ΠC) plasmas by with liver failure, INR fails to yield a PT expression indethe manual tilt-tube technique by adding 200 mL of thromboplastin pendent of the thromboplastin used and only activity reagent to 100 mL of plasma and the clotting time in seconds was percentage expression may provide a common internarecorded. Results were expressed in seconds (PTs), activity percent- tional scale of PT reporting. (HEPATOLOGY 1996;24:1392age (PTp), ratio (PTr), and INR. To obtain PTp expression, a saline 1394.