Internal quality control practice of thyroid disease related tests and imprecision analysis in China

Internal quality control (IQC) has a long and well-established role in clinical laboratories and the quality of laboratories has achieved great improvement in China. However, the practice of IQC varies significantly between institutions and many problems still exists. Consequently, the Chinese National Center for Clinical Laboratories has been undertaking monthly nation-wide surveys of current IQC practice of tests since 2010 to monitor laboratory quality. Thyroid disease related tests were chosen for this research.

Different numbers of laboratories in China participating national external quality assessment (EQA) schemes of Total Thyroxine (TT4), Total Triiodothyronine (TT3), Free Thyroxine (FT4) and Free Triiodothyronine (FT3) tests, and Thyroid Stimulating Hormone (TSH) measurements, were required to report the IQC information though the national external quality assessment (EQA) network platform.

Survey data showed significant variability in all aspects of IQC practice. More than half of the laboratories are using a single concentration level of IQC material and up to 28.6% of the laboratories only use 1(2s) or 1(3s) to monitor IQC results for FT3, TT3, FT4, TT4, and TSH. The medians of the average time intervals of two control tests for FT3, TT3, FT4, TT4, and TSH are 33.6, 35.4, 33.6, 35.4, and 33.6 hours, respectively, more or less 1.4 days. When quality specifications based on biological variation are applied to imprecision evaluation, only 46.3%, 52.1%, 31.3%, 12.8%, and 5.86% laboratories meet the minimum performance for FT3, TT3, FT4, and TT4, 24.5%, 23.6%, 12.8%, and 5.86% of the all meet the desirable performance, and 4.4%, 3.9%, 2.5% and 3.0% of the all meet the optimal performance. While it shows a higher percentage of acceptable laboratories (98.1%, 87.9% and 39.0% meeting the minimum, desirable and optimal performance, respectively) for TSH.

Not-well-designed IQC practices may affect the effectiveness of laboratory IQC and, thus, the adequacy of a laboratory to monitor system performance. Consequently, IQC practice should be designed according to performance of measure method and instrument. Both clinical laboratories and the government should make efforts to improve quality of clinical testing to ensure the patients' safety.