Clinical impact of citrate-containing tubes on the detection of glucose abnormalities by the oral glucose tolerance test

Background: Plasma glucose levels provide the cornerstone of diabetes evaluation, and so it is crucial that clinical laboratories provide accurate and reliable plasma glucose results. To prevent in vitro glycolysis, citrate is used. Here, we present the first study on the 75-g oral glucose tolerance test (OGTT) using the currently available new citrate-containing tubes in liquid and granular forms and the previous sodium fluoride (NaF) for the diagnosis of carbohydrate metabolism disorders and gestational diabetes mellitus (GDM) according to the American Diabetes Association (ADA) guidelines. Methods: The 75-g OGTT was performed in 147 volunteers, 83 of whom were pregnant women. Blood was collected in NaF/K 3 ethylenediaminetetraacetic acid (EDTA) and NaF/Na 2EDTA/citrate in liquid form in tubes in Brescia and in NaF/K 2Ox and NaF/Na 2EDTA/citrate in granular form in Vicenza. Glucose was measured within 3-4 h from the OGTT. The mean biases were calculated and compared with the desirable bias (<+/- 2.1%). Results: OGTT glucose concentrations were higher in citrate tubes when compared to NaF-containing tubes. When citrate tubes were used, GDM increased to 12.5 and 11.7% in Brescia and Vicenza, respectively. Impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and diabetes mellitus (DM) increased to 36.7, 6.7 and 3.4%, respectively, in Brescia. In Vicenza, an increase of 47 and 1.9% in IFG and IGT, respectively, was found. Conclusions: OGTT glucose measurement in citrate-containing tubes was shown to be more effective than those containing only NaF in diagnosing carbohydrate disorders. This new glycolysis inhibitor seems to be a necessary preanalytical tool for accurate and reliable plasma glucose results.