Glycosuria

Glycosuria describe the presence of glucose in the urine and it is usually denoted in a urine test with a positive (+) mark.

The glucose present in the urine is the result of the renal excretion. The kidneys should only excrete glucose in the urine when blood glucose concentration becomes excessively elevated (at levels up to 160 and 190 mg/dL). Those levels suggest hyperglycemia and are common in case of suffering diabetes. Below that threshold, the kidneys reabsorb almost all the glucose.

However, some circumstances may alter the renal threshold for glucose. For example, in case of kidney problems (renal glycosuria) or in pregnancy where small amounts of glycosuria may be present.

The glucose test in the urine gives diagnostic information about the glucose metabolism. It must be studied along the blood sugar.

A positive result in this test means that there is a significant presence of glucose in the urine. It is usually due to:

• Hyperglycemia (as a consequence of diabetes mellitus)
• Decreased renal threshold for glucose (due to renal disorders such as Fanconi syndrome)

Urine glucose test can be a part of diabetes screening and diabetic patients may use this test to monitor their disease progress.

The glucose test in the urine should be performed on fasting samples because the blood glucose concentration can fluctuate throughout the day. A normal person may have glycosuria following a meal with a high sugar content.

Glycosuria is measured frequently using reagent strips or dipsticks. The dipstick changes its color in the presence of glucose because of the reaction of the glucose oxidase enzyme.

In laboratories, there are automated machines that perform the analysis, but it is also possible to buy strips that let you analyze a urine sample at home. They comprise up to 10 or more different reagents or chemical pads to perform different urine tests at the same time.

The urine glucose test must be negative to be considered within normality. The presence of glucose in the urine should be below 15 mg/dl to be considered negative.

If the test give a positive result for glucose in the urine (glycosuria), it is recommended to study the glucose or sugar in the blood.

The diagnostic meaning for a positive result depends on the existence or not of hyperglycemia (a blood sugar value above the normal range):

• Glycosuria with hyperglycemia
  • Diabetes mellitus
  • Endocrine disorders
    • Acromegaly
    • Cushing's syndrome
    • Hyperthyroidism
    • Pheochromocytoma
  • Pancreatic disease
    • Cystic fibrosis
    • Severe chronic pancreatitis
    • Hemochromatosis
    • Pancreatic cancer
  • CNS (Central Nervous System) dysfunction (especially if they affect the hypothalamus)
• Glycosuria without hyperglycemia
  • Pregnancy
  • Renal disorders (renal glycosuria)
    • Kidney failure
    • Fanconi syndrome
    • Renal tubular acidosis
    • Cystinosis

Some drugs may interfere causing a positive result for glucose in the urine:

• Corticosteroids
• ACTH (Adrenocorticotropic hormone)
• Thiazides
• Oral contraceptives
• Ascorbic acid
• Homogentisic acid
• Salicylates
• Levodopa
• Captopril