Renal threshold

In physiology, the renal threshold is the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine. When the renal threshold of a substance is exceeded, reabsorption of the substance by the proximal convoluted tubule is incomplete; consequently, part of the substance remains in the urine. Renal thresholds vary by substance – the low potency poison urea, for instance, is removed at much lower concentrations than glucose. Indeed, the most common reason for the glucose renal threshold ever being exceeded is diabetes.