Too Much Sugar in the Urine

A close-up of a urine analysis test strip.
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Sugar in the urine is called glycosuria or glucosuria. "Glyco" or "gluco" refers to the sugar glucose, and uria means "in the urine." Usually the amount of sugar in the urine is too low to be detected. If you have had sugar in your urine, you should get follow-up testing to check your blood sugar level. Glycosuria is usually caused by elevated blood glucose, or hyperglycemia.

Renal Threshold

Glucose is the body's preferred energy source. As blood circulates through the kidneys, glucose is filtered through the glomeruli, then reabsorbed by the renal tubules so that it remains in the bloodstream. Normally, virtually all glucose is reabsorbed. However, if the level of blood glucose exceeds the amount that the tubules can reabsorb completely, the excess glucose "spills over" into the urine, causing glycosuria. The level at which this occurs is called the renal threshold. The average renal threshold for glucose is often given as 180 mg/dL, however, it can vary widely. It can be very low in children and pregnant women, tends to rise with age and can be much higher in those with long-standing diabetes.

Elevated Blood Glucose

Glycosuria is usually caused by hyperglycemia, which in turn usually indicates impaired glucose tolerance or diabetes. Other causes of hyperglycemia include hyperthyroidism, acromegaly, Cushing's syndrome and dumping syndrome. The blood glucose level may also be elevated by stress hormones during severe anxiety or pain, infections such as meningitis or IV glucose, or parenteral, nutrition.

Screening for Diabetes

Urine glucose testing is most commonly used to screen for diabetes. If glucose is found in the urine, further testing is needed. Ketones in the urine could also be a sign of diabetes and requires follow-up testing. Your health care provider will usually check your fasting blood glucose level and perhaps your A1C level, which gives an indication of your blood sugar level over a two- to three-month period.

Renal Glycosuria

Less commonly, glycosuria can be caused by renal glycosuria, or renal diabetes. This occurs when the blood sugar level is normal but the renal threshold for glucose is reduced, so that sugar spills into the urine at a lower blood sugar level. If you are pregnant, you may have a lower renal threshold. Glycosuria in pregnancy should still be followed up with further testing, as it may be a sign of gestational diabetes. Other causes of renal glycosuria include Fanconi's syndrome, Lowe's syndrome, cystinosis, Wilson's disease, interstitial nephritis and heavy metal poisoning.