Generality
The presence of glucose in the urine ( glycosuria ) is a characteristic symptom of diabetes mellitus, which looks at case from the adjective "mellitus" to the typical sweet taste taken from the patient's urine.
What's this
When blood glucose levels ( blood glucose ) are normal, the kidneys - by filtering the blood - pass a minimal amount of sugar into the urine.
Glucose starts to appear in the urine ( glycosuria ) when the amount of sugar in the blood increases and exceeds the so-called "renal resorption threshold". At this point, the kidneys are no longer able to prevent the elimination of sugar with urine.
The renal glucose reabsorption threshold may vary from person to person: on average, if blood glucose levels are above 180-200 mg / dl, the presence in the urine may begin to be detected.
Once detected, glycosuria requires confirmation by determination of fasting glucose and / or oral glucose loading test (OGTT).
Why do you measure
The analysis of glucose in the urine serves to highlight the presence of significant levels in the blood; this condition is associated with diseases that result in elevated blood sugar (such as diabetes mellitus, Cushing's syndrome, hyperthyroidism, etc.).
In diabetic patients, if the results are consistently negative on multiple urine samples, the test confirms that the disease is well controlled.
Note
The glucose test in the urine (glycosuria) is often required together with the fasting blood glucose test, but should not be considered as a diagnostic test for diabetes.
Normal values
Under normal conditions, glucose is not present in the urine, since usually the kidney does not eliminate this valuable substance for the body.
Glycosuria occurs only when glucose is present in the blood in excessive amounts and, precisely, when its concentration (glycemia) exceeds 180 mg / dl (limit value of sugar reabsorption by the kidney).
The glucose values in urine considered normal correspond to:
- Absent: in an extemporaneous urine sample (collected at a single time of day);
- 30-90 mg: in the urine of 24 hours.
Note : the published values are indicative and the reference interval of the exam can change according to age, sex and instrumentation used in the analysis laboratory. For this reason, it is preferable to consult the ranges listed directly on the report. It should also be remembered that the results of the analyzes must be evaluated as a whole by the general practitioner, who knows the patient's medical history.
High glucose in urine - Causes
Glucose is an essential nutrient for our body, which certainly cannot afford to waste it through urine.
By virtue of its small size, the glucose circulating in the blood is easily filtered by the renal glomerulus, passing into the so-called preurine. Immediately afterwards, at the level of the proximal nephron tubule, the vast majority of the filtered glucose is reabsorbed and transferred to the blood. When the blood sugar rises too much, however, the renal reabsorption mechanisms become saturated and a more or less important portion of the sugar is lost.
In particular, the presence of glucose in the urine begins to be significant when the blood sugar level exceeds 160-180 mg / dl. This value represents the so-called renal glucose threshold, that is the glycemic level in which some nephrons begin to let slip small but significant amounts of glucose.
From 300 mg / dl onwards, the kidney's reabsorption capacity is completely saturated and any excesses are completely eliminated through the urine.
The renal glucose threshold varies slightly from person to person and some individuals - especially children and pregnant women - may experience glycosuria even at lower glucose levels.
However, during pregnancy this symptom should not be underestimated, as any gestational diabetes must necessarily be controlled.
Finally, there is a very rare condition, the so-called renal glycosuria, in which the sugar is eliminated in the urine due to a defective functioning of the renal tubules; in this case there is glycosuria even without hyperglycemia.
OTHER POSSIBLE CAUSES OF GLYCOSURIA:
- acromegaly (GH is a hyperglycaemic hormone);
- ecstasio of cortisol: Cushing's syndrome, infections, diseases and more generally stressful conditions, intake of corticosteroids or ACTH (cortisol is a hyperglycaemic hormone);
- hyperthyroidism (at high doses thyroid hormones promote gluconeogenesis and glycogenolysis);
- pheochromocytoma (hormone that secretes catecholamines, hyperglycemic hormones);
- advanced chronic pancreatitis, pancreatic neoplasia and advanced cystic fibrosis (due to insufficient insulin synthesis);
- hemochromatosis, asphyxia, tumor or cerebral hemorrhage (hypothalamus);
- extensive burns, uremia, severe hepatic failure, sepsis, cardiogenic shock, use of thiazide or estroprogestinics diuretics.
The blood is filtered by the nephrons (in the figure), which represent the functional unit of the organ (the smallest structure capable of performing all the functions it is intended for).
The blood flows into each nephron through an afferent arteriole, which branches, like a skein, into a dense network of capillaries called glomerulus and surrounded by Bowman's capsule.
At the glomerular level occurs the so-called filtration; the blood components filtered by the capillaries, called pre-urine together, are collected by Bowman's capsule. From this structure arises a contiguous series of tubules, called, in order, proximal convoluted tubule, Henle's loop and distal convoluted tubule, for a total length of 5 centimeters. Along these tubules, the filtrate undergoes reabsorption phenomena that concentrate the urine to avoid excessive water losses and recover the substances necessary for the body. Among these, glucose is reabsorbed at the proximal convoluted tubule, crosses the epithelium and returns to the blood
Consequences
The expulsion of glucose through the urine, caused by the excessive increase in blood sugar, could be considered a very useful defense mechanism against marked increases in blood sugar. Unfortunately, however, this condition causes a great loss of water with urine, which can cause severe dehydration; urine rich in glucose also provides fertile ground for bacterial growth and increases the risk of urinary infections.
Low glucose in urine - Causes
Low levels of glucose in the urine are not usually associated with medical problems and / or pathological consequences, therefore they are not considered clinically relevant.
Glycosuria is not always abnormal: the increase in glucose in the urine can be observed, for example, immediately after a meal with a high carbohydrate content.
In the absence of pathological causes, glycosuria can also be found in subjects subjected to the infusion of fluids containing sugar (dextrose) or after taking certain drugs (aspirin, ascorbic acid, etc.).
How to measure it
The amount of glucose in the urine can be measured with a simple test. Just put the reactive part of the strip in contact with urine and within a minute the strip changes color depending on the presence or absence of glucose. It is very important to use only the devices suggested by the doctor, respecting the indications; for example, if high doses of vitamin C (above 1 g / day) are taken, the result could be falsely negative for the reducing activity of ascorbic acid: in doubtful cases it is advisable to repeat the test with urine collected 10 hours after the last hiring.
Preparation
The test is normally performed by collecting an extemporaneous sample (ie a single moment of the day) of fresh urine in a clean and dry container, then taking it to analyze quickly.
It is not advisable to perform the test on the first morning urine that has accumulated in the bladder for several hours.
The glucose test in the urine can be performed on the entire sample of urine emitted during the day (24-hour urine; overall glycosuria), for example from 8 am to 8 am on the following day.
Interpretation of Results
Under normal conditions, glucose is not present in the urine, since the kidneys provide for its reabsorption. If it appears in the urine, giving rise to glycosuria, it signals an incorrect use of sugars by the body.
Hyperglycemic glycosuria
Glycosuria can occur when the amount of glucose in the blood increases and exceeds the renal threshold (ie the capacity for tubular reabsorption); under such circumstances, the kidneys are no longer able to prevent their elimination with urine.
The disease that most typically involves hyperglycemic glycosuria is diabetes mellitus. For this reason, in addition to blood glucose determination, diabetic subjects are recommended to periodically check for glucosuria. By repeating this analysis on different urine samples, the effectiveness of treatment with insulin and other hypoglycemic drugs can be monitored.
Other diseases that may be associated with hyperglycemic glycosuria are Cushing's syndrome and hyperthyroidism.
The last important note to note is that the presence of hyperglycemic glycosuria makes the diabetic patient more sensitive to lower urinary tract infections.
Normoglycemic glycosuria
Glycosuria in the presence of normal or low levels of blood glucose may appear when the kidneys are unable to reabsorb this sugar due to impaired functionality.
Normoglycemic glycosuria may depend on an acquired or hereditary defect of the renal tubule, mainly determined by the congenital deficiency of some enzymes or by advanced chronic kidney diseases.
The pathological situations that can lead to the presence of normoglycemic glycosuria also include: Fanconi syndrome, use of nephrotoxic drugs, carbon monoxide intoxication, acromegaly and pheochromocytoma.
The presence of glucose in the urine can also result from chronic inflammation of the pancreas or from cancer processes affecting the organ itself. Other possible causes include hemochromatosis, cystic fibrosis, extensive burns, uremia, severe liver failure, sepsis and brain tumors.
