It takes acid, rather than ice, to freeze glucose

Abstract

Plasma glucose levels provide the cornerstone of diabetes evaluation. Unfortunately, glucose levels drop in vitro due to glycolysis. Guidelines provide suitable conditions which minimize glycolysis, such as immediate centrifugation or the use of ice/water slurry storage containers. For obvious practical reasons, most laboratories use blood collection tubes containing glycolysis inhibitors. We describe the effect of a variety of commonly used blood collection tubes on in vitro stability of glucose. Furthermore, we looked at the validity of the assumption that glycolytic activity is minimal when blood is kept in an ice/water slurry. Sodium fluoride alone does not reduce in vitro glycolysis in the first 120 minutes after phlebotomy. Addition of citrate almost completely prevented in vitro glycolysis, but showed a positive bias (0.2 mmol/l) compared to control. This is partly due to a small drop in glucose level in control blood, drawn according to the current guidelines. This drop occurs within 15 minutes, in which glycolysis has been described to be minimal and acceptable. NaF-EDTA-citrate based test tubes provide the best pre-analytical condition available. Furthermore, glucose levels are not stable in heparinized blood placed in an ice/water slurry. We strongly advise the use of NaF-EDTA-citrate based test tubes in diabetes research.

Liquid citrate acidification introduces significant glucose bias and leads to misclassification of patients with diabetes

“…However, among the Glucomedics tubes, no hemolyzed sample was detected, contributing to their greater suitability for routine practice compared to NaF/KOx tubes. Previous investigations confirmed a high hemolysis rate in NaF/KOx tubes, but also in NaF/EDTA/citrate tubes containing granular additive [15,25]. Interestingly, Jones and Böttiger found that some plasma samples collected in Terumo Venosafe Glycaemia ® tubes, showed dark brown coloration after centrifugation [26].…”

“…Our results confirm that Glucomedics tubes (containing liquid sodium EDTA/NaF/liquid citric acid/sodium citrate) are superior in inhibiting glycolysis compared to NaF/KOx alone, and also compared to LiH plasma processed according to current recommendations (sample chilling and centrifugation within 15 min from blood collection). Unreliability of chilled LiH samples in glycolysis prevention was also shown by Van der Berg et al who measured glucose in chilled samples at different time points within 15 min from venipuncture [25]. The drop in glucose concentration was attributed to the time needed for the sample to cool.…”

“…The drop in glucose concentration was attributed to the time needed for the sample to cool. According to their results it takes about 3 min in ice-water slurry to chill the sample to 5 °C [25]. A recent investigation by del Pino et al compared glucose measured in heparin, NaF/KOx, citrate buffer/ NaF/potassium EDTA and serum tubes, supplied by Terumo Europe (Leuven, Belgium), under controlled preanalytical conditions.…”

Long-term stability of glucose: 96-h study using Terumo Glycaemia tubes

“…Other studies which reported an altered recovery modified the study duration ( ≤ 24 h) and/or the storage temperature but relied on fewer samples [3,7,14].…”

Laboratory diagnosis of gestational diabetes mellitus

“…2 Nevertheless, there is evidence that glycolysis continues for up to 4 hours in samples containing fluoride and that inhibition of glycolysis in vitro may be more effective when a citrate buffer is used. 10 Hence, when a special report was published in 2011, the revised recommendation was that to inhibit glycolysis, a fluoride sample tube should be placed immediately in an ice-water slurry, and the plasma should be separated within 30 minutes. 11 If that cannot be achieved, a tube containing a rapidly effective glycolysis inhibitor, such as citrate buffer, should be used (see Figure 2).…”