In a healthy individual, almost all of the glucose filtered by the renal glomerulus is reabsorbed in the proximal convoluted tubule. The amount of glucose reabsorbed by the proximal tubule is determined by the body's need to maintain a sufficient level of glucose in the blood. If the concentration of blood glucose becomes too high (160-180 mg/dL), the tubules no longer reabsorb glucose, allowing it to pass through into the urine.
It is important to note that glucose may appear in the urine of healthy individuals after consuming a meal that is high in glucose. Fasting prior to providing a sample for screening eliminates this problem.
Conditions in which glucose levels in the urine are above 100 mg/dL and detectable include:
- diabetes mellitus and other endocrine disorders
- impaired tubular reabsorption due to advanced kidney disease
- pregnancy - glycosuria developing in the 3rd trimester may be due to latent diabetes mellitus
- central nervous system damage
- pancreatic disease
- disturbances of metabolism such as, burns, infection or fractures