Two trials of external quality assessment were performed in 2015, with 13 test items grouped into four test categories. The first trial materials were sent on May 19, 2015 and the second trial was performed on November 9, 2015 with 13 items including tumor markers, thyroid hormones, cardiac marker troponin (troponin T or troponin I), and procalcitonin (PCT) as biomarkers by immunoassay methods. The bone marker, carboxy-terminal collagen crosslinks (CTX) was replaced by procalcitonin since 2014, because a limited number of institutions performed assays with CTX. External quality surveys of 13 immunoassay test items with 16 control materials were conducted, as scheduled. In total, 13 control materials were used, which consisted of six tumor markers, namely alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), carcinoma antigen (CA) 125, carbohydrate antigen (CA) 19-9, human chorionic gonadotrophin (HCG), and prostate specific antigen (PSA). In addition to tumor markers, 5 thyroid markers, namely thyroid hormone (T)3, T4, thyroid stimulating hormone (TSH), free T4, and thyroglobulin (TG) were included. Furthermore, troponin, as a cardiac marker, and procalcitonin, as a new biomarker, have been adopted since 2014. Five home-made pooled sera and 3 commercial control sera were used as survey materials. MAS Tri-point Liquimmune level 3 (Medical Analysis Systems Inc., USA) was used for thyroid hormones. Procalcitonin and troponin control materials were from Elecsys Precis Control Varia and Elecsys Precis Control Troponin (Roche, Germany), respectively. The number of laboratories participating in the external quality assessment for Immunoassay Subcommittee was 719 institutions in the first trial survey (response rate 98.7%) and 730 institutions in the second survey (94.9%). The test items most frequently used in immunoassays were TSH (93.2%, 93.1%), free T4 (90.3%, 90.2%), and AFP (89.4%, 89.0%), whereas recently adopted biomarkers were less frequently used: troponin I (36.6%, 37.1%), procalcitonin (24.1%, 26.7%), and thyroglobulin (10.3%, 10.7%). The quality of the laboratories participating in the survey seems to be continuously improving, according to their peer group results.

Keywords: Immunoassay, Quality assurance, External quality assessment, Surveys, Tumor marker, Thyroid marker, Cardiac marker, Troponin, Procalcitonin

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