title: Calibration verification of the International Normalized Ratio.
abstract: The International Normalized Ratio (INR) system for reporting the prothrombin time (PT) is essentially a calibration activity intended to standardize PT reporting across various reagent/instrument systems. However, complete standardization of PT reporting through the INR has been difficult to achieve for a variety of reasons, including inaccurate assignment of thromboplastin International Sensitivity Indexes (ISIs) and specific (local) reagent/instrument effects. Until now, the individual laboratory has not been able to easily verify the accuracy of its INR. Using standard lyophilized plasmas with INR values assigned against IRP RBT/90 rabbit thromboplastin, the authors present a method that allows a laboratory to locally verify its range of accuracy for the INR. The method is illustrated on a single coagulometer with two thromboplastin lots of differing sensitivity (Pacific Hemostasis Thromboplastin-DS and Thromboplastin-D from rabbit sources, with respective International Sensitivity Indexes of 1.20 and 1.97). In this illustration of the method, the accuracy of Thromboplastin-DS was superior to that of Thromboplastin-D. Interpretation of the data and cautions regarding the use of standard plasmas for calibration verification are discussed. Using this method, a reportable range of accuracy at a given error tolerance can be established locally for INR measurements within a laboratory. Laboratories of any size can apply this method to study the accuracy of their INR reagent/instrument systems, thus performing calibration verification. When used in conjunction with assessments of assay precision, this method can help laboratories to select better reagent/instrument systems and thereby produce more accurate and more clinically meaningful INR results.
authors.affiliation: Corning Clinical Laboratories, Teterboro, New Jersey, USA.
authors.forename: G C
authors.initials: GC
authors.lastname: Critchfield
authors.forename: S T
authors.initials: ST
authors.lastname: Bennett
authors.forename: W R
authors.initials: WR
authors.lastname: Swaim
mesh_terms: D000818:Animals; D002138:Calibration / Q000592:standards*; D006403:Hematologic Tests / Q000592:standards*; D006801:Humans; D008433:Mathematics; D011517:Prothrombin Time; D011817:Rabbits; D012015:Reference Standards; D015203:Reproducibility of Results