Results of external quality control of HbA1c in Croatian medical laboratories indicated that POCT system differ from immunoassay methods

Background: HbA1c as valuable marker in management of diabetes is measured in the most of medical laboratories in Croatia. Aim of this study is to present the results of external quality control assessment (EQA) in Croatian medical laboratories for HbA1c. Material and methods: Results were obtained from 93 laboratories that participated in cycle of EQA scheme in 2013.The control sample was commercial, lyophilized human blood specimen with normal HbA1c value. The results were entered on-line, as a dual system of reporting: DCCT (%) and IFCC (mmol/mol), and DCCT results were analyzed. Outliers (N=14) were excluded according to Tukey´s model and mean (X), standard deviation (SD) and coefficient of variation (CV) were calculated. According to quality specifications established in CROQALM, the allowable deviation from the mean was ±5%. Results: The results were divided in two groups according to the method (immunoassay and colorimetric method). For immunoassay methods (82 participants, six types of instruments), reported results were: X=5.4%, SD=0.18, CV=3.3%. For colorimetric method (11 participants, POCT instrument), results were: X=9.8%, SD=1.94, CV=19.8%. Immunoassay group indicated acceptable CV (<5%) while results (CV) obtained by colorimetric method (POCT analyzer) were far outside of acceptable limits. Conclusion: Immunoassay methods for HbA1c determination indicated very good inter- laboratory comparability. High CV in the group of POCT analyzer revealed poor comparability within that method group. Therefore, it can be concluded that only a minority of participants that reported results obtained on POCT analyzers demonstrated low inter-laboratory agreement.