The Current Status of CA15-3 Measurement Based on a Commutable External Quality Assessment Program

The goal was to evaluate the external quality assessment (EQA) performance of breast cancer-related tumor marker CA15-3.

CA15-3 EQA materials were distributed to each participating laboratory by cold chain transportation each round, and the laboratories returned results through the official website. The participating hospitals were grouped according to the testing reagents and methods. The median was taken as the target value. Evaluation criterion, 20.83%, was based on desirable specification derived from intra- and inter-individual biological variation. The robust CV was used to evaluate the variation trend between laboratories. The choice of high, medium, and low concentration levels was used to compare the differences between detection systems, and the pass rate was used to evaluate the test quality of the laboratory.

In the five CA15-3 EQA from 2023 to 2025, the number of participating laboratories was 504 - 817. There was a significant difference in the composition ratio of hospitals at different levels between the rounds. In the classification of reagents, the range of robust CV was 6.48 to 7.63, and the robust CV of the first EQA of CA15-3 in 2025 was lower than that of the second EQA in 2024; the pass rates of the two quality assessments in 2024 were both higher than that of the second EQA in 2023. Of a total of 63 pairwise comparisons, the vast majority showed statistically significant differences. There was no statistical difference in the results between the three reagents of brand f, brand c and others at low and medium levels. In the classification of methods, there was no statistically significant difference in the robust CV and pass rate of CA15-3 among the five inter-laboratory quality assessments from 2023 to 2025. At low and medium levels, there was no significant difference between the results of some methods. At high levels, there were significant differences between any two groups except D - C and A - B.

The pass rate of CA15-3 was increasing, and the robust coefficient of variation was decreasing. There are differences among different detection reagents and methods, so different reference intervals and treatment cut-off values should be used to provide more accurate clinical service.