The Role of Kidney in Glucose Homeostasis — SGLT2 Inhibitors, a New Approach in Diabetes Treatment

Vasileios Andrianesis; John Doupis


Expert Rev Clin Pharmacol. 2013;6(5):519-539. 

In This Article

Transport Maximum & Threshold of Glucose Reabsorption

For most substances actively re-absorbed or secreted in the kidney, there is a transport maximum. Transport maximum for glucose is expressed by the maximum transporting capacity of the SGLT transportation system. Excessive glucose is not reabsorbed and consequently passes into urine. Transport maximum for glucose tubular transport system in adult humans is about 375 mg/min.[21] Normally, filtered glucose is about 125 mg/min. Transport maximum can be exceeded in case there is a significant increase of GFR or in case the blood glucose concentration overpasses the level of 300 mg/dl (product of GFR 125 ml/min and blood glucose level of 300 mg/dl is 375 mg/min).[21] Remarkable is the fact that glucose starts to appear in the urine at a blood glucose level of 200 mg/dl, which corresponds to a filtered load level much lower than transport maximum. This glucose blood concentration (200 mg/dl) and the filtered load of 250 mg/min are termed as the threshold for glucose. The main reason for the difference between the levels of transport maximum and threshold is that some nephrons excrete glucose in a lower than transport maximum level, and the transport maximum for the kidneys is reached when all the nephrons reach their maximal capacity to reabsorb glucose.[21]