Analytical validation of therapeutic drug monitoring (TDM) on AxSYM Abbott analyzer

Introduction: Careful monitoring of drug concentration (therapeutic drug monitoring, TDM) is essential for a large number of drugs. The aim of this study was to evaluate analytical performance of Abbott AxSYM analyzer for therapeutic drug monitoring of theophylline, carbamazepine, phenobarbital and valproic acid.

Materials and methods: For the purpose of analytical validation following parameters were determined for all analytes: inaccuracy (bias), within-run and between-run imprecision and measurement uncertainty. Additionally, concentration of valproic acid was compared with the previously used analytical system (TDx FLx Abbott analyzer) for 30 patients’ samples.

Results: Inaccuracy results (bias) were as follows: for theophylline from –3.66% to –5.84%; for carbamazepine –0.46% to 1.00%; for phenobarbital –1.83% to –8.08% and for valproic acid from –1.01% to –5.65%. The highest coefficient of variation (CV) for within run imprecision was observed for phenobarbital (7.07%) and the lowest for theophylline (2.71%). The highest CV for between run imprecision was observed for carbamazepine (4.73%) and the lowest for theophylline (2.94%). The highest measurement uncertainty was observed for phenobarbital assay (21.7%) and the lowest for carbamazepine (10.7%).

Passing-Bablock regression analysis of valproic acid comparison on two analyzers showed statistically significant, but clinically insignificant deviation in slope of the regression equation (b = 1.121; 95% CI = 1.028–1.197); however the Cusum linearity test proved that there was a linear relationship between two methods.

Conclusion: In conclusion, analytical validation fulfilled all previously established criteria and could be implemented in a routine laboratory work.