Comparison of Quick and Owren prothrombin time with regard to the harmonisation of the International Normalised Ratio (INR) system

Prothrombin time (PT) is tested mostly to monitor patients on oral anticoagulant treatment. The International Normalised Ratio (INR) was introduced to improve and harmonise PT results and therapeutic range globally for patient care and the scientific literature. We studied the Quick PT in 179 patients and the Owren PT in 137 patients on oral anticoagulant therapy using two different reagents for the two methods of measuring PT. We assessed the clinical significance of the INR results obtained by each method using the two reagents and compared the Quick and Owren methods. We conclude that with the Quick method individual INR results differed from each other too much clinically, while using the Owren method individual INR results were clinically acceptable. Our opinion is that we should develop the INR system using the Owren PT method rather than the Quick to improve patient care.