Objective:the aim of this study was to evaluate the imprecision of the method used to determine TSH (Thyroid Stimulating Hormone) levels from dried blood spots in a newborn screening program and how the value of the coefficient of variation influences the total error of the method.
Methods:A short-term evaluation of imprecision was compared with the imprecision of the method assessed over five years. The coefficient of variation from the best quality control period and the worst quality control period were used. For Bias assessment mean results from the external quality program were used. Total Error was calculated with Bias and Coefficient of Variation values. A freely available software was used for standard deviation and coefficient of variation profiling.
Results:The values of the coefficient of variation for the short-term were lower than values obtained in worst quality control period but higher than in the best quality control period. Total error was higher than the accepted value for low-level control in the worst quality control period. Images obtained with the software showed that for high-level control coefficient of variation is concentration-dependent but this finding is not similar for low-level control.
Conclusions:Total Error of the Method may be subject to change in time. Initial evaluation of imprecision must be performed on a short term analysis but a continuous evaluation should be performed as the performance of a method may change in time. The evaluation should be performed on clinically significant levels for each parameter.