The Glucose Fasting Urine test is a simple, non-invasive screening tool. It checks for the presence of glucose (sugar) in your urine after a period of fasting. Healthy kidneys reabsorb glucose, so there should be none in your urine. The presence of glucose (glycosuria) is a strong indicator that your blood sugar levels are high enough to "spill" over, a hallmark of diabetes. This simple urine sample provides a clear, qualitative sign, prompting the need for a more definitive blood test to confirm a diagnosis.