title: The Australasian Reference Thromboplastin: II. Are corrected prothrombin ratios valid?
abstract: A comparative study was made of 2 thromboplastins, the Australasian Reference Thromboplastin, and Simplastin, in a large group of patients on long-term Warfarin therapy. 373 individual samples were obtained. Calibration constants were obtained for those patients with prothrombin ratios within the therapeutic range, and for those well outside the therapeutic range, and found to be different. Study of the relationship between the 2 thromboplastins indicates that comparability is linear only within a specified limited range of prothrombin ratios. At the two extreme ends the relationship is curved, suggesting a logarithmic relationship. Attention is drawn to the need of caution in interpretation of corrected ratios calculated on a linear relationship especially when the ratio is above 4.0 as this may have clinical implications.
mesh_terms: D003374:Coumarins / Q000494:pharmacology / Q000627:therapeutic use; D006470:Hemorrhage / Q000097:blood / Q000517:prevention & control; D006801:Humans; D008433:Mathematics; D011517:Prothrombin Time; D013925:Thromboplastin / Q000592:standards*; D014859:Warfarin / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: D003374:Coumarins; D014859:Warfarin; D013925:Thromboplastin