Preanalytical sample handling of venous blood: how to ensure your glucose measurement is accurate and reliable

Measurement of blood glucose is a standard biochemical test requiring optimum preanalytical sample handling. Glucose measured in plasma from tubes containing sodium fluoride is recommended but serum from serum‐gel tubes may be used in research situations. To help inform best practice, we assessed glucose stability in plasma and serum samples subjected to different preanalytical conditions. Fasting samples were taken from 10 non‐diabetic volunteers into fluoride/EDTA and serum‐gel tubes. Whole blood samples were pipetted into aliquots, placed on crushed ice or left at room temperature. Aliquots were centrifuged at 0, 2, 12, 24, and 48 hours. When neither ice nor centrifuge were available, plasma glucose was stable for 48 hours (96% of baseline); serum glucose degraded to 8% of baseline. When centrifuged and left at room temperature, plasma glucose was stable for 48 hours (101% of baseline) but, by 24 hours, serum glucose had fallen (94% of baseline). The result of un‐centrifuged plasma on ice was stable (96% of baseline) at 48 hours; serum glucose had dropped to 92% of baseline by 12 hours. Plasma glucose and serum glucose were constant for 48 hours when separated and placed on ice within 2 hours: plasma glucose 101% of baseline; serum glucose 100% of baseline. Separated serum resting on the serum plug fell to 94% of baseline by 12 hours at room temperature and to 92% of baseline by 48 hours on ice. Clinically, we recommend that glucose is measured on plasma taken from fluoride tubes. Analysis should be undertaken as soon as practicable. In the research setting, glucose can be measured on plasma or serum but samples must be centrifuged and chilled soon after venepuncture and analysed within 48 hours. Copyright © 2013 John Wiley & Sons. Practical Diabetes 2013; 30(3): 128–131