A-002 The Prevalence of the High Sensitivity Cardiac Troponin I Outlier and False Positivity Rates on Beckman Coulter Access DxI

Abstract

Abstract Background The false positive elevation in high sensitivity cardiac troponin I (hsTnI) can be triggered by many factors, for example, fibrin clots, heterophile antibodies, or other sources of troponin interferences. These interferences lead to inaccurate hsTnI results. These inaccurate results described in the literature as the “outliers”. Published studies use statistical tools to identify the outliers based on the discrepancies between the two repeat values. Depending on the instrument platform and the study design, the outlier rate for the conventional troponin I assay was reported from 0.44% to 1.01% (1, 2). In our laboratory, the false positivity rate for the conventional troponin assay on Beckman Coulter DxI platform was determined as 1% (unpublished data). This study aim was to determine both the statistically and clinically significant outliers for hsTnI assay on the Beckman Coulter Access DxI instrument in the academic medical center clinical laboratory setting. Methods A unique test repeat protocol was created. Two parallel hsTnI measurements are conducted in lithium heparin tubes (BD Vacutainer) on Beckman Coulter DXI 800 systems. When the difference between the two results is greater than 30%, a third repeat is automatically ordered and run after additional centrifugation at a higher relative centrifugal force. The outlier determination is based on assessing the difference between the first two values using previously described statistical analysis tools (1). The clinically significant outlier was determined by counting positive results in the first two runs which are not unconfirmed by the third run, i.e., false positive results. Gender specific cutoffs, 14 ng/L for female and 19 ng/L for male, were applied to identify the positive results. Overall, 2935 patients’ results were evaluated during the study. Results Based on the analysis of the first two repeat runs, out of 2935 samples 16 samples, or 0.54%, were identified as the statistical outliers. 2 out of these 16 outliers, or 12.5%, were negative results. Taking into consideration the third repeat data, 13 out of 2935 samples, or 0.44%, were identified as false positive results. Only 9 out of 13 false positive results, or 69.2%, were identified using the statistical approach above. Conclusion The false positivity rate of hsTnI testing has dropped significantly from 1% to 0.44% in a setting of our laboratory. Our refined repeat protocol approach significantly increases the clinician’s confidences in the hsTnI results by capturing potential false positive results. This approach addresses the outliers at an additional expense like reagents, instrument wear and tear, and labor. Therefore, a more robust methodology is still desired by the industry.