Abstract:

Objective　To evaluate the performance of thyroid hormone testing all over the country. Methods　The difference percentage between resultsand target values was estimated according to external quality assessment（EQA） data， and the imprecision was obtained according to internal quality control（IQC） data [coefficient of variation（CV）]. The EQA evaluation criterion in our country and biological variation quality specification were used to analyze the acceptabilities of difference percentage and imprecision in each group. The sigma（σ） value was calculated with the formula of σ=[total allowable error（TEa）- bias]/CV. The scatter diagram was drawn， and the distribution of σ value was analyzed. Results　The mean of CV and the median of difference percentage for thyroid stimulating hormone（TSH） were the lowest of all， while those for triiodothyronine（T3） were the highest. Regardless of quality specifications， the acceptabilities of imprecision and difference
percentage for TSH were the highest， and those for thyroxine（T4） were the lowest. The scatter of T4 in the scatter diagram of σ value was entirely low， 63.0% and 98.2% σ＜3. However， that of TSH was entirely high， 75.6% and 72.9% σ≥3. Conclusions　σ value is a simple and visible method to evaluate the testing performance. The performance of TSH is better than the others， but T4 is worst of all.

Key words: Thyroid hormone, Sigma value, Imprecision, Difference percentage