The procedure involves fasting overnight for at least 8 hours. Upon arrival at the healthcare facility, a baseline blood sample is taken to measure fasting glucose levels. The child is then given a glucose solution to drink, usually flavored to make it more palatable. Subsequent blood samples are taken at specific intervals, typically at 30 minutes, 1 hour, 2 hours, and sometimes 3 hours, to measure how well the glucose is metabolized.