A COMPARISON OF LINEAR AND ORTHOGONAL REGRESSION-ANALYSIS FOR LOCAL INR DETERMINATION IN ECAA COAGULOMETER STUDIES

International sensitivity index calibrations based on the W.H.O, recom mended method depend on orthogonal regression analysis, As this is not readily available in statistical packages, comparison has been made w ith simple linear regression analysis in a study of coagulometer effec ts on the International Normalized Ratio (INR) at 155 European centres , Sets of seven lyophilized normal and 20 lyophilized artificially dep leted abnormal plasmas were provided with five coumarin test plasmas a nd two European Concerted Action on Anticoagulation reference thrombop lastins (low International Sensitivity Index (ISI) human and high ISI rabbit). Local ISI based on the artificially depleted lyophilized plas mas using conventional orthogonal regression gave good correction for local coagulometer effects on the human reagent and minimal correction with the rabbit reagent INR. Results were considerably worse after at tempts at correction using calibration based on linear regression anal ysis with both reagents. The results indicate that calibration of coag ulometer prothrombin time systems using simple linear regression is no t appropriate.