Glucose Tolerance Test Protocol (GTT) The glucose load can be administered orally (via a gavage needle or it is time for the procedure). List of Exhibits. Exhibit. Informational flyer for Oral Glucose Tolerance Test, aged 12 years and older. Primary SP's OGTT processing protocol. The glucose tolerance test is a medical test in which glucose is given and blood samples taken Usually the OGTT is performed in the morning as glucose tolerance can exhibit a diurnal rhythm with a A laboratory may continue to collect blood for up to 6 hours depending on the protocol requested by the physician.