[National external quality assessment and comparability of assays for tumor markers measurements].

Objective: To evaluate the performance of tumor markers (TM) measurements in clinical laboratories by external quality assessment (EQA) and investigate the comparability of assays for TM.

Methods: Ten quality control sera specimens were distributed to 586 laboratories by global Express Mail Services (EMS) in March 2008 and tested twice with 5 specimens each time. Analytes were total prostate specific antigen (PSA), free PSA, carcinoembryonic antigen (CEA), alpha fetoprotein (AFP), human chorionic gonadotrophin (HCG), beta-HCG, carbohydrate antigen 19-9 (CA19-9), cancer antigen 15-3 (CA 15-3), cancer antigen 125 (CA125), beta-2-microglobulin and ferritin. The collected data were divided into peer groups according to analyzers or methods and the median of peer group was adopted as the target value (TV) separately after outlier removal. Two standard deviations of the median were set as the limit of difference.

Results: The first TM EQA results of 2008 showed that the pass percentage of all participating laboratories ranged from 87.3% (CA125) to 95.5% (beta-2-microglobulin). And the second batch ranged from 83.5% (HCG) to 94.0% (beta-2-microglobulin). The coefficient variances (CVs) of intra-group values determined by automatic analyzers were lesser than 15% for each test of every specimen. The CVs of radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) were over 20% and 50% respectively. The inter-group medians of 9 tests showed CVs>20% with HCG 13.4% and ferritin 15.7%. The CV of paired medians of some automatic analyzers was small and showed no statistical significance (all Z<1.890, all P>0.05).

Conclusion: The analytical performance of automatic analyzers is superior to RIA and ELISA. There is an excellent comparability within automatic analyzers for TM measurements and a lack of comparability within RIA and ELISA. Noncomparability is found in over 80% of TM assays.