Glycosurie

Glycosurie, or glycosuria, is the presence of glucose in urine. In healthy individuals, the kidneys reabsorb almost all filtered glucose in the proximal tubules, and the renal threshold for glucose reabsorption is about 180 mg/dL (approximately 10 mmol/L). When blood glucose rises beyond this threshold or when tubular reabsorption is impaired, glucose appears in the urine.

Causes of glycosuria are diverse. The most common is hyperglycemia from diabetes mellitus or stress-related hyperglycemia, including pregnancy. Less common are renal causes such as renal glycosuria due to defects in proximal tubule glucose transporters (for example SGLT2/SLC5A2 or SGLT1/SLC5A1), inherited renal glycosurias, or proximal tubulopathies such as Fanconi syndrome. Drugs or therapies that promote urinary glucose excretion, notably SGLT2 inhibitors used in diabetes treatment, can also cause glycosuria.

Diagnosis relies on urine testing and clinical context. A standard urine analysis or dipstick test can detect glucose but does not quantify it or distinguish its cause. Confirmation typically involves measuring urine glucose quantitatively and assessing plasma glucose levels to evaluate for hyperglycemia. If plasma glucose is elevated, evaluation for diabetes using standard criteria (fasting plasma glucose, random plasma glucose with symptoms, or HbA1c) is indicated. If plasma glucose is normal, renal glycosuria or proximal tubulopathy should be considered, and further evaluation of renal function and other causes (e.g., infections) may be warranted.

Clinical significance and management depend on the underlying cause. Glycosuria often signals hyperglycemia and warrants assessment for diabetes. Renal glycosuria is usually benign but may require monitoring. Management targets the underlying condition: glycemic control for diabetes, or observation and monitoring for renal causes; in pregnancy, screening for gestational diabetes is important.