Glucose variation in centrifuged serum and lithium-heparin gel tubes stored for up to 96 hours at room temperature or 4 °C.

This study aimed to verify glucose stability within centrifuged serum and lithium-heparin tubes stored at room temperature (RT) or 4 °C. Sixty paired serum (plus gel separator), lithium-heparin (plus gel separator) and K-EDTA tubes were centrifuged within 30 min from collection. Thirty serum and lithium-heparin tubes were then stored at RT, whilst the other 30 serum and lithium-heparin tubes were kept at 4 °C. Complete cell blood count was performed in serum and plasma after centrifugation, as well as in K-EDTA paired whole blood tubes. Glucose was measured immediately after centrifugation and 3, 6, 24, 48, 72 and 96 h afterwards. Immeasurable blood cells values were found in serum, whilst residual leukocytes and platelets were present in lithium-heparin plasma. Regardless of storage conditions, glucose concentration decreased 3 h after centrifugation in lithium-heparin tubes, displaying uninterrupted reduction until 96 h. Mean decrease per hour was higher in plasma tubes stored at RT than at 4 °C. Performance specification was exceeded between 6 and 24 h of storage in most plasma tubes. Glucose concentration significantly decreased in serum tubes between 24 and 48 h, regardless of storage conditions. The mean glucose variation never exceeded performance specification throughout the study period. Mean glucose decrease per hour in plasma was not associated with blood cells counts before and after centrifugation, and was probably attributable to the presence of blood cells entrapped within the gel. Delayed glucose measurement in centrifuged serum tubes may be clinically viable up to 96 h, whilst it may be unadvisable in centrifuged lithium-heparin tubes.