Summary: This study investigated the effect of lag times between blood sampling and glucose analysis on plasma glucose results from 6 volunteers. Our aim was to determine whether glucose tolerance test protocols should include instructions on the handling of blood between sampling and analysis. Plasma glucose levels remained stable for all lag times between spinning and analysis. With a lag time between blood sampling and spinning, plasma glucose levels did not remain stable, and a significant lowering of plasma glucose was found in the first 2 hours of lag. With increased lag time there was no further decrease in plasma glucose levels. Glucose tolerance test protocols should include clear guidelines on the handling of the blood samples between collection and analysis, and the spinning down of samples needs to be prioritized.