Wide acceptance of the international normalised ratio (INR) and thromboplastins with low international sensitivity indices (ISIs) has inadvertently led to the application of the INR to patients other than those on anticoagulation treatment. I examined the degree of factor deficiency for a given INR in patients with liver disease and controls receiving stable-dose warfarin. The degree of factor V and VII, but not prothrombin, deficiencies for a given INR were greater in liver patients than controls. The INR measured with a low-ISI thromboplastin can quantify the coagulation status of patients with liver disease, but should not be interpreted as having the same meaning as the INR in patients receiving warfarin.