Daily monitoring of a control material with a concentration between LOB and LOD improves the accuracy of highly sensitive troponin assay

Background-aim Rapid and safe rule out of acute myocardial infarction in patients admitted to emergency department (negative predictive value N99%) can be achieved by setting limit of blank (LOB) or limit of detection (LOD) of highly sensitive cardiac troponin assays (hsTn) as decision thresholds. Accurate calibration of hsTn in the low concentration range is therefore of the upmost importance for this application. Even relatively small analytical variations may indeed influence the proportion of patients who could be identified as suitable for discharge. To monitor baseline drifts and calibration accuracy at very low hsTn concentrations, in March 2017 we introduced a serum pool with a concentration between LOB and LOD as an additional internal quality control material (IQC3). Here we show the impact of this additional quality tool on EQAS performance. Methods In our laboratory, we measure hsTnT on two interchangeable Roche Cobas e411 platforms (LOB and LOD: 3 and 5 ng/L, respectively) and participate to the UK-NEQAS, which includes a low concentration sample (LCS) in each monthly exercise. We evaluate EQAS results according to an allowable total error (TEa) of ±22.5% (biological variability derived) between our result and the mean of participants using the same measuring system. The IQC3 is prepared from fresh leftover human sera with hsTnT concentrations between 3 and 5 ng/L and stored at –20 °C in 250-μL aliquots. IQC3 target value and acceptability range are preliminarily determined by calculating mean ± 30% of 10 measurements performed in optimal conditions. The IQC3 is then assayed twice daily and after every new calibration. If results are “out of control”, immediate corrective actions are implemented before reports related to the samples analysed in the affected run are issued. Results Before the IQC3 introduction, we measured hsTnT on LCS from 26 EQAS exercises, with 11 results (42.3%) not meeting TEa. After the IQC3 introduction, only one out of 21 exercises (4.8%) did not meet TEa (P = 0.009 between the two periods). Results for the failed exercise were 9.1 vs. 7.2 ng/L (TE +26.4%). Conclusions Implementing an IQC at hsTn concentrations between LOB and LOD is vital for assuring the suitable accuracy at such low, but clinically relevant concentrations.