Glucose meters: What's the laboratory reference glucose?

BACKGROUND: The accuracy of glucose meters is evaluated by comparing their results with those from a reference laboratory glucose analyser. The main scientific societies recommend the use of a prompt glycolysis inhibitor such as citrate for an accurate glucose determination. In the present preliminary study, we discuss the bias between capillary and plasma glucose measured concentrations, determined in two Italian clinical laboratories, using tubes containing an NaF and citrate mixture in liquid and granular form. METHODS: 139 volunteers in whom 75 g OGTT was requested were recruited. Basal capillary glucose was determined using Abbott FreeStyle Precision Neo in Brescia (n=63), while clinical laboratory reference P-glucose was determined using tubes containing NaF/K(3)EDTA and liquid NaF/Na(2)EDTA/citrate. Basal capillary glucose was determined using a Roche Cobas Accu-Chek Inform II in Vicenza (n=76), while P-glucose was determined using tubes containing NaF/K(2)Ox and NaF/Na(2)EDTA/citrate in granulated form. Reference P-glucose was determined with a hexokinase method on Dimension Vista systems. Differences between capillary and reference P-glucose were evaluated according to ADA/ISO 15197:2013 specifications. RESULTS: 96.82% and 97.37% of capillary determinations were within specifications when liquid and granular citrate mixture tubes were used, respectively. Conversely, only 73.02% and 80.26% of determinations were within criteria using NaF. CONCLUSIONS: It's important to know what is the laboratory reference glucose in evaluating glucose meters' accuracy. The evaluation of glucometers' accuracy with respect to a reference laboratory may be wrong if tubes containing only NaF are used due to in vitro glycolysis. Only tubes containing citrate mixture permit the correct evaluation of glucose meters' accuracy.