Comparison of Citrate Buffer with Sodium Fluoride as Additives in Determining Glycemia

The objectives of this study are to compare the effect of sodium fluoride and citrate on the stability of glucose in samples maintained at room temperature up to three hours, and to assess the clinical impact in the O'Sullivan test results after changing the additives in the collecting tubes.

The selected population was pregnant women between the 24th and 28th week of gestation, who were at the health center to undergo the O'Sullivan test as part of the screening program for GDM (gestacional diabetes mellitus). Two blood samples were extracted from each patient: one using a tube with citrate and sodium fluoride buffer (tubes Vacuette Glucomedics citrate, 2 mL, Ref 454347) (tube C) and another containing just sodium fluoride (BD Vacationer tubes FX fluoride, 2 mL, Ref 368920) (tube F). The statistical treatment of the data was performed using SPSS version 24 and Method validator. Finally, we assessed the real clinical impact of replacing tubes C for tubes F in the classification of pregnant women. To do so, we collected the results of O'Sullivan tests conducted in our hospital during a year, all of them done in tubes F, and we applied the mean difference calculated in T = 1 to estimate the number of pregnant women that should be reclassified.

The average glycaemia in tubes C are significantly greater than average glycaemia in tubes F (p < 0.05) at all time points. The clinical impact assessment was done over the 6,526 O'Sullivan test results with a prevalence of positive tests of 21.35%. The prevalence using tubes C instead of tubes F estimated with mean differences previously calculated is 33.45%.

The glucose concentrations in tubes F stored at room temperature up to 3 hours were significantly lower (p < 0.05) than those measured in tubes C stored under the same conditions. We observed that it is in the first minutes after extraction, while the samples are collected and aliquots done, that the glucose consumption occurs in tubes F, but not in tubes C. There is a need to change the preanalytical conditions to prevent any loss of glucose. This will enable more accurate diagnosis and management of diabetes mellitus.