Time-Dependent Analysis of Blood Glucose Stability in Sodium Fluoride Versus Plain Blood Collection Tubes

OBJECTIVES: Sodium fluoride (NaF) tubes are routinely recommended for blood glucose estimation because of their glycolysis-inhibiting properties. However, NaF inhibits enolase, a downstream glycolytic enzyme, and does not immediately prevent glucose consumption by blood cells. This raises the following questions: How does glucose stability compare between NaF plasma and plain serum over time? Does NaF offer better glucose preservation than plain serum? Does prompt separation of blood cells improve glucose stability? This study aimed to compare glucose stability in NaF plasma and plain serum at different time intervals and assess the effect of prompt cell separation on glucose preservation under routine laboratory conditions. Materials and methods: This prospective observational study included 172 paired blood samples collected simultaneously in NaF and plain serum tubes. Samples were categorized into three groups: Group 1, plasma from NaF tubes; Group 2, serum from plain tubes; and Group 3, serum separated after centrifugation(using LabTop centrifuge at 3000 rpm for 10 minutes) and aliquoted into microcentrifuge tubes. Groups 1 and 2 were analyzed (using clinical chemistry analyzer Bonavera Chem 200, Biogeny Diagnostics Pvt. Ltd., Beacon Group, Surat, India) at <4 hours (baseline), four to six hours, 12-14 hours, and 24-26 hours after collection while stored at room temperature. Group 3 samples were analyzed after 24 hours. Percentage variation in glucose concentration from baseline was calculated. RESULTS: The mean difference between plain serum and NaF plasma within four hours of collection was 0.44%, with individual variation ranging from -0.62% to 3.36%. In NaF plasma, the mean decline in glucose concentration from baseline was 2.47% at four to six hours, 4.31% at 12-14 hours, and 9.97% at 24-26 hours. Corresponding individual variations ranged from 0.46% to 5.12%, 2.99% to 8.56%, and 3.96% to 17.47%, respectively. By contrast, the mean glucose decline in unseparated serum samples was 8.69%, 45.94%, and 75.59% at the respective time intervals. Glucose concentrations in aliquoted serum remained stable after 24 hours, showing <1% variation from baseline. CONCLUSION: The consistent and substantial decline in glucose concentrations over time in both serum and plasma samples that remain in contact with blood cells highlights the critical importance of prompt cell separation to minimize pre-analytical glycolysis and ensure reliable glucose measurements. Notably, even when blood is collected in NaF tubes, delayed centrifugation and separation of plasma from blood cells may still permit considerable glucose loss. This raises concerns about the presumed advantage of fluoride-containing tubes over plain tubes when prompt sample processing is not ensured. In a hospital-based lab or referral lab with a rapid processing workflow, the use of a single plain serum tube can yield accurate glucose results, along with other biochemical tests, although it is not universally recommended as for peripheral collection centers. This can prevent the extra cost burden of fluoride vials for diagnostic labs and also decrease the extra burden of blood samples on patients. This also decreases the burden of biomedical waste generated in the form of fluoride vials, making it more sustainable and environmentally friendly. Further multicenter studies are warranted before recommending changes to existing specimen collection guidelines.