Expansion
Glucose appears in urine once plasma glucose exceeds about 10 mmol/l
Expansion
Glucose is freely filtered and completely reabsorbed in the proximal tubule by SGLT2 (about 90 per cent) and SGLT1 (the remainder).
- Renal threshold: about 10 mmol/l (180 mg/dl), the plasma level at which glucose first appears in urine
- Transport maximum (Tm): about 375 mg/min, the point at which all transporters are saturated
- Splay: the rounded shoulder between them, caused by heterogeneity in the transport capacity of individual nephrons
Clinical applications:
- Diabetes mellitus: glycosuria once plasma glucose exceeds the threshold, causing an osmotic diuresis with polyuria and dehydration
- Pregnancy: the threshold falls, so glycosuria can occur with normal blood glucose
- Familial renal glycosuria: an SGLT2 defect causing glycosuria with normal blood glucose
- SGLT2 inhibitors deliberately lower the threshold, producing glycosuria and thereby lowering blood glucose, with additional cardiovascular and renal benefits