Uncertainty Evaluation and Internal Quality Control of ELISA Test for Food Allergens (in Egg and Milk) Using Control Samples

Abstract

We evaluated measurement uncertainty and performed internal quality control of an ELISA test for allergens in egg and milk, using control samples. For the evaluation of measurement uncertainty, the following three important factors were identified: 1) Differences in test-kit lots, 2) Different-day reproducibility, 3) Same-time reproducibility. A three-stage nested design was used, and the combined standard uncertainty of the three factors mentioned above was calculated based on the results obtained. Measurement uncertainty was defined as the expanded uncertainty obtained by multiplying the combined standard uncertainty by a coverage factor of two. As a result, the expanded uncertainty of egg was 1.9 μg/g when the total egg protein concentration was 13.4 μg/g, and the expanded uncertainty of milk was 1.8 μg/g when the total milk protein concentration was 13.5 μg/g. For the internal quality control, we first set the reference range of the measured value of the control sample, using the obtained combined standard uncertainty as an index. Each control sample was then measured for every test, and we concluded that the test was performed without any errors, when the result of the control sample was within the reference range. Second, the measured values of the control samples were plotted on a graph for continuous monitoring. This enabled us to check whether inspection accuracy was maintained. There were no large chronological changes and no major differences between the standard deviations of the control samples and the combined standard uncertainty in egg or milk. Therefore, it was determined that the dispersion was at an acceptable range and inspection accuracy was maintained.