According to WebMD, high blood sugar levels cause excess glucose in the urine. High blood sugar levels are common in people with uncontrolled diabetes. When an individual's blood sugar level is high, it can spill into the urine. Glucose in the urine can also occur if the kidneys are suffering from damage or disease.
MedlinePlus explains that glucose is typically not found in the urine. When an individual tests positive for glucose in the urine, further testing is required. High levels of glucose in the urine of pregnant women can indicate gestational diabetes. High levels of glucose in the urine can also indicate renal glucosuria, a condition that causes the kidneys to leak glucose into the urine.
According to Mayo Clinic, glucose is filtered by the glomeruli and reabsorbed by the proximal tubule. In normal cases, glucose is not excreted through the urine. However, if the amount of glucose filtered through the glomeruli exceeds the capacity of the tubule, excess glucose is excreted through the urine. Rare conditions such as Fanconi syndrome, interstitial nephritis, Wilson's disease and hereditary glucosuria can cause decreased reabsorption, resulting in glucose in the urine. Most cases of elevated glucose in the urine are connected to elevated glucose levels in the serum. Urine glucose screening is used as a screening test for diabetes mellitus.