What is the renal threshold?
Sugar enters the human body with foods that include carbohydrates. The name “sugar” combines two carbohydrates - glucose and fructose. However, speaking of him as a laboratory indicator, they always mean only glucose. Why does sugar appear in urine with various diseases? How to regard it? What is glucosuria? Let's talk about this in more detail.
Normally, glucose in the intestine is absorbed into the bloodstream, enters the cells of the body and penetrates into them under the action of insulin. It is used as an energy source and as a plastic material.
Excess glucose is partially stored in the liver as glycogen. Another part of it through the blood vessels enters the kidneys and is filtered in their glomeruli in the so-called primary urine. Primary urine from the glomeruli enters the proximal renal tubules. There, sugar with the help of special carrier proteins is absorbed and enters the bloodstream again. As long as blood sugar does not exceed a known value called the renal threshold, it is completely reabsorbed from primary urine. Therefore, in the urine of a healthy person there should not be sugar. The renal threshold is an individual value, but on average it is 10 mmol / l. In children and pregnant women, it is lower - about 7 mmol / l.
If blood sugar exceeded 10 mmol / l, then, once in primary urine, it cannot be completely reabsorbed. Its too much. Some part of it enters the final urine and is excreted along with it from the body. Thus, sugar appears in the urine, which is determined by laboratory tests.
Normally, only traces of sugar can be in the urine. This is a concentration not exceeding 0.2 mmol / L. It is not detected by conventional methods. Laboratory urinary sugar excretion is called glucosuria. It is physiological and pathological.
What conditions does sugar appear in urine?
What diseases and conditions cause sugar in the urine? What does it mean? Physiological glucosuria may be associated with an increase in blood sugar during stress, physical exertion, the use of certain drugs, for example, steroidal anti-inflammatory drugs; during pregnancy, when consumed in a large number of sweets, honey. It does not last long, it is low and disappears with a decrease in blood sugar.
Pathological glucosuria happens:
- independent of the condition of the kidneys,
- caused by a violation of the reabsorption or filtration function of the kidneys.
In the first case, sugar in the urine with diabetes is the most common example of glucosuria. With this disease, blood sugar rises due to a lack of insulin or the inability of cells to respond to it. If blood glucose exceeds the renal threshold, sugar will appear in the urine without fail.
An increase in blood glucose in diseases such as Itsenko-Cushing's disease, pheochromocytoma, thyrotoxicosis can also lead to an increase in blood glucose. Severe chronic liver diseases, in which its function of glucose deposition is impaired, can also be the cause of its appearance. In all these cases, the appearance of sugar in the urine is a sign that there is too much sugar in the blood.
With glucosuria of the second type, blood sugar may be normal, and its appearance in the urine is due to the fact that renal function is impaired. In this case, renal filtration can be increased and reabsorption can be reduced.
How to pass urine for analysis?
Determine sugar in urine collected per day. The first, usually morning, portion of urine for analysis is not taken. All subsequent days, including the morning portion the next day, are collected in a jar. The jar must be kept in the refrigerator, otherwise part of the sugar will collapse, and the result of the analysis will be underestimated. For example, collect urine from 7 a.m. this morning to 7 a.m. tomorrow. Urine should be measured as accurately as possible and recorded, what is its daily amount.
Then the urine should be mixed, poured a little into a small jar and taken to the laboratory. To find out how much sugar a person gives out per day, you need to multiply the amount of sugar in 1 liter by the daily amount of urine, which is usually done by the laboratory assistants themselves.