scope:

CLSI document H54 reviews limitations of the INR system and provides a rationale for performing local PT/INR verification with recommendations as to when calibration may be indicated. The method of certified plasma preparation and method of INR value assignments are described in detail. Also included are the recommended INR range that certified plasmas should cover and recommended number of certified plasmas required for local ISI calibration. A protocol for performing calibration of PT systems is provided. Methods of calculating local ISI are included, as well as the procedure for creating a calibration line in order to interpolate a direct INR.

To facilitate improved precision and accuracy of PT assay results, enhance laboratory standardization, and thereby optimize patient results and care, the guideline has been divided into two parts. Though both may be educational for all users, Part I is primarily intended for manufacturers of the reagents and instruments used in the PT/INR system, and for manufacturers of material such as certified plasmas to standardize the PT assay; Part II is written for laboratory professionals responsible for the performance of prothrombin time (PT) assays.