Use of delta control methods and reference change values in the evaluation of clinical biochemistry test results

Objective: The workload of medical laboratories is increasing day by day due to reasons such as the increase in the number of patients applying to hospitals to receive health services, the expansion of test panels and the increase in the number of samples coming to medical laboratories. Due to this increasing workload, it is not possible for laboratory specialists to evaluate each test result manually in a standard and reliable way. For this reason, autoverification (AV) systems have begun to be used in medical laboratories to automate the postanalytical phase. In AV, limit control rules such as reference range, delta control, reference change value (RCV) are used to evaluate test results. Test results that do not violate these rules are reported automatically, while test results that do not violate these rules are presented to the laboratory specialists for review. In this way, the time spent by medical laboratory specialists for approval and the workload of the laboratory are reduced. There is no consensus on which of these rules should be applied. In our study, we aimed to contribute to the literature on reference range (RR), delta control and reference change value (RCV) based limit control rules for biochemistry tests and which limit control rule would be most appropriate in evaluating test results by applying various modifications (reference range ± total allowable error (TEa)) to these rules. Materials and Methods: 15 biochemistry tests, which were studied at Pamukkale University Faculty of Medicine Medical Biochemistry Laboratory between 01.07.2022 and 01.10.2022 and whose individuality index was <1.4, were included in the study. For this purpose, 928326 test results of these 15 tests were retrospectively examined from the laboratory information management system (LIMS) and evaluated according to limit control rules. Three methods were used as limit control rules: First, the reference range rule using population based limit values provided by the manufacturer; the second is the delta control rule determined according to the 2.5 and 97.5 percentiles of our past patient results, and the third is the RCV rule, which is calculated both classically and logarithmically using the analytical coefficient of variation obtained from internal quality control results and the intra-individual biological coefficient of variation obtained from the EFLM (European Federation of Clinical Chemistry and Laboratory Medicine) database. Additionally, evaluations were made by making modifications to some rules. The percentages of tests that were not verified according to limit control rules for all tests studied, in total and for each test separately, were calculated and compared with each other. Results: When all test results studied were evaluated together, automatic verify rates using limit control rules were found to be between 62.28% and 87.01%. With the reference range rule, the automatic verify rate was 74.38%. Changes to limit control rules, such as reference range ± TEa, have reduced the rate of unverified tests. The highest automatic verify rate (87.01%) with the "2 x RR x %99RCV (logarithmic)" rule; the lowest automatic verify rate (62.28%) was obtained with the "95% RCV (logarithmic)" method. The highest verify rate, between 92.44% and 94.03% for sodium, chloride and potassium tests, was obtained with the "reference range ± TEa" method. Using limit control rules for creatine, glucose, cholesterol and urea tests, automatic verify rates were between 80.38% and 81.63%. Conclusion: The addition of limit control rules as a component of AV algorithms in the evaluation of clinical biochemistry test results can increase the number of automatically verified test results and significantly reduce the workload of the medical biochemistry specialists. Each laboratory should decide which rule to apply by evaluating limit control rules according to the characteristics of its patient population and workload.