MATRIX EFFECTS AND THE PERFORMANCE AND SELECTION OF QUALITY-CONTROL PROCEDURES TO MONITOR PO2 MEASUREMENTS

We have assessed how variation in the matrix of control materials woul d affect error detection and false-rejection characteristics of qualit y-control (QC) procedures used to monitor Po-2 in blood gas measuremen ts. To determine the expected QC performance, we generated power curve s for s(mat)/s(meas) ratios of 0.0-4.0. These curves were used to esti mate the probabilities of rejecting analytical runs having medically i mportant errors, calculated from the quality required by the CLIA'88 p roficiency testing criterion and the precision and accuracy expected f or a typical analytical system. When s(mat)/s(meas) ratios are low, th e effects of matrix on QC performance are not serious, permitting sele ctions of QC procedures based on simple power curves for a single comp onent of variation. As s(mat)/s(meas) ratios increase, single-rule pro cedures generally show a loss in error detection, whereas multirule pr ocedures, including the 3(1s) control rule, show an increase in false rejections. An optimized QC design is presented.