Glucose

Glucosuria is defined as the presence of glucose in urine. Diabetes mellitus is the most important and most frequent cause of glucosuria. In a healthy kidney, glucose is filtered in the glomerulus and almost completely reabsorbed (99.7%) in the proximal tube. A glucosuria occurs when the threshold of reabsorption of the proximal tube is exceeded, i.e. at a blood level between 9-10 mmol/L (160-180 mg/ dl).

Calculation of glucose reabsorption in case of normal glycemia or hyperglycemia: examples
Normal glycemia Hyperglycemia
Plasma-Glucose 5.6 mmol/L 16. 7 mmol/L
Glomerular filtrate 125 ml/min
Filtered glucose 0.7 mmol/min 2.1 mmol/min
Reabsorbed glucose 0.7 mmol/min 1.7 mmol/min
Maximal glucose reabsorption capacity 1.7 mmol/min
Glucosuria absent 0.4 mmol/min
(576 mmol/24h
or 6.8 g/dL)

Physiological glucose excretion is not detectable with the test strip (sensitivity too low). It is normally <1mmol/24 h. In the first morning urine, the amount of glucose should not exceed 1.1 mmol/L (~ 20 mg / dl).

Test strip, from left to right: comparison scale, then a negative result than a positive result. The latter corresponds to a glucose value between 100 and 300 mg/dl or 5.5 and 17 mmol/L.

Clinical relevance

Diabetes mellitus

Glucose screening in urine is performed in every patient. Diabetes mellitus is a common disease and screening for glucose in urine is a simple and efficient method. However, absence of glucosuria does not exclude the diagnosis.

Diabetes mellitus screening is especially important in the following situations::

  • Obesity
  • Hyperlipidemia
  • Hyperuricemia or gout
  • Arterial hypertension
  • Coronaren, zerebralen oder peripheren Zirkulationsstörungen
  • Hepato-biliary symptoms
  • Chronic infection of the urinary or respiratory trac
  • Chronic dermatological diseases
  • People older than 40
  • People with a familial history of diabetes mellitus

Note:lab follow-up of diabetes should include serum glucose and HbA1C.

However, a single glucose result is not sufficient to diagnose diabetes, because there are other causes of hyperglycemia.

Renal glucosuria

  • Pregnancy glucosuria
    Pregnant women can have a moderate fasting and post-prandial glucosuria. This form of glucosuria disappears after delivery.
  • Familial renal glucosuria
    Glucosuria is present while the blood glucose concentration is normal. Renal function is also not affected. The glucosuria can vary between <10-100 g/24 h. This tubular disorder is very rare and genetically heterogeneous.
  • Glucosuria in Fanconi syndrome
    Fanconi syndrome can be observed in various congenital metabolic disorders.
  • Glucosuria can be due to toxic or immunological renal tubule damage.

Detection limit

The detection limit in ascorbic acid free urine is about 2.2 mmol/L (40 mg/dL). This means that even a low level of glucosuria can be detected with great confidence.

Potential errors

Ascorbic acid (Vitamin C) can interfere with the enzymatic measurement of glucose in urine.