Sodium Fluoride tubes versus plain tubes for In vitro blood glucose analysis

Background: In terms of diagnosis and management of diabetes mellitus, the most commonly requested core biochemistry test worldwide is measurement of glucose in blood. Despite the wide use of sodium fluoride (NaF) as the specimen preservative, its use has been critically questioned. Objective: This study investigated the stability of glucose in blood obtained into plain tubes in comparison with sodium fluoride/potassium oxalate (NaF/K2C2O4) tubes in a routine laboratory setup. Methods: Sixty one pairs of blood specimens were collected into plain tubes and NaF/K2C2O4 tubes. Following separation of plasma (NaF/K2C2O4 tubes) and serum (plain tubes), glucose concentration was measured. Five determinants were obtained; the baseline glucose value, glucose concentrations at one, two, four and six hours after collection of blood into NaF/K2C2O4 or plain tubes. Results: A high rate of haemolysis was observed in NaF/K2C2O4 tubes when compared with that of plain tubes (11% vs. 4%). No effect of tube type on serum/plasma glucose concentration (p>.05) was noted until two hours post collection. A significant reduction (p<.001) of blood glucose in plain tubes was observed in comparison with plasma measurements after four hour spot collection. Conclusion