Comparison of sodium fluoride and serum separator tubes for blood glucose estimation – What’s the best option?

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The efficacy of sodium fluoride tubes in preserving glucose was compared against a serum separator tube with a gel barrier. We compared the fall in blood glucose levels in a fluoride - oxalate tube against levels in a serum separator tube. A heparinized tube was used as a standard.45 samples were drawn from healthy patient volunteers and distributed into the different tubes. Patients on medications or with chronic kidney disease were excluded. Glucose estimation was done by glucose oxidase-peroxidase method using a semi-automated colorimetric analyser. Samples were immediately centrifuged and stored at room temperature. The fall in glucose levels in each tube was measured at predefined time intervals of 1, 2, 4, 12 and 24 hours.There was no statistically significant difference in the glucose values measured in the fluoride and serum separator tubes at all time intervals from 1 to 24 hours. There was no statistically significant difference in the glucose values measured in all three tubes until 4 hours. However, there was an error beyond acceptable limits (for medical decision making as per CLIA criteria) in the difference in values between the fluoride and heparin tubes at 2 and 4 hours.Thus, there is no difference between use of a fluoride tube or a serum separator tube for up to 24 hours. A serum separator tube can be used when many analytes are to be measured in the same sample and a fluoride tube can be used when only glucose is to be estimated. A heparinized tube will suffice if glucose estimation will be done within one hour of collection.