As long as blood glucose levels do not exceed 10 millimoles per litre (renal threshold for glucose reabsorption, above which any excess is eliminated through the urine), there should be no glucose in the urine, with an exceptional trace in very concentrated urine. The presence of sugar in the urine (glycosuria) can have various causes.
Blood glucose levels above the renal threshold for reabsorption can be seen in uncontrolled diabetes or more rarely following an extremely sugary meal. A decreased threshold for glucose reabsorption can be seen during pregnancy, in cases of severe vitamin D deficiency or inherited kidney disease, or as a result of medication or exposure to heavy metals. Taking large quantities of vitamin C can produce false negative results, while contamination of the specimen container can produce false positive results. In the presence of actual glycosuria, a blood glucose measurement is the starting point for investigating more specific causes.