Urine glucose, renal glucose threshold, glycated hemoglobin, and fructosamine:
Urinary glucose
This refers to the sugar excreted in the urine, mainly glucose. The kidney is one of the major organs in the human body, serving as a “filter.” When blood flows through the kidney, the glomeruli in the kidney act like a filter, separating many waste products and toxic substances from the blood, converting them into urine which is then excreted to maintain the body’s normal state. During the filtration process, some beneficial substances can also be filtered into the renal tubules. The renal tubules have strong reabsorption capabilities, and the beneficial substances can be completely or partially reabsorbed back into the blood.
Similar to this, glucose in the urine is mostly reabsorbed back into the blood, so in healthy individuals, there is only a very small amount of sugar in the urine, which is undetectable by conventional testing methods, thus resulting in a negative urine glucose test. The renal tubules have a limited ability to absorb glucose. When the blood glucose concentration exceeds a certain value, the glucose in the renal glomerular filtrate cannot be completely reabsorbed, and it is excreted in the urine, resulting in diabetes. In normal renal function, the higher the blood glucose concentration, the more urine glucose there will be.
Kidney sugar threshold is an abstract concept referring to the lowest blood sugar level that causes diabetes. When blood sugar exceeds this threshold, diabetes occurs, and when it is below the threshold, there is no sugar in the urine (urine sugar is negative), so it is also known as the renal threshold of blood sugar (J-6 out). The normal renal sugar threshold is 8.89~10mmol/L. Elderly patients often have poorer kidney function, which increases the renal sugar threshold. Urine sugar only appears when blood sugar far exceeds 10mmol/L. During pregnancy, women’s renal sugar threshold decreases, so even when blood sugar is below 8.89mmol/L, urine sugar can still occur.
Glycated hemoglobin and fructosamine
Many proteins in the body can bind to glucose, a complex process called glycation. Glycated proteins are called glycated proteins. The process of protein glycation is related to the glucose level in the blood. The higher the blood sugar, the more glycation occurs. Therefore, in recent years, diabetes experts have regarded the level of glycated proteins as an indicator of diabetes control. Glycated proteins may also be related to the pathogenesis of chronic complications of diabetes.
Glycated hemoglobin:
Hemoglobin is the main chemical component of red blood cells. When blood sugar rises in diabetes patients, hemoglobin can be glycated into glycated hemoglobin. Glycated hemoglobin is the earliest discovered and most widely used glycoprotein, including many components. Among them, HbA1C is a more accurate indicator of blood sugar changes. Since the average lifespan of human red blood cells is 120 days, and the metabolic cycle of hemoglobin is basically the same as that of red blood cells, glycated hemoglobin levels often reflect the control of diabetes within the past 1-3 months.
There are many methods for measuring glycated hemoglobin, mainly including chromatography such as long-column chromatography, microcolumn chromatography, and high-pressure liquid chromatography. Colorimetry, electrophoresis, and radioimmunoassay are rarely used or not widely applied due to limitations or other factors.
Fructosamine:
It is an indicator reflecting the glycation level of plasma proteins, which is simpler than measuring HbA1C. Since plasma proteins are metabolized quickly, the half-life of albumin is generally 9-21 days, so it can only reflect the changes in blood sugar within the past 1-3 weeks. Generally, the normal value of fructosamine is less than 2.65 mmol/L. Values above this indicate significant hyperglycemia or poor diabetes control.
The changes in glycated hemoglobin and fructosamine, besides the above significance, have recently been proposed by some scholars to possibly benefit the early diagnosis of diabetes. The dangers of both indicators for monitoring diabetes please refer to the content of diabetes monitoring.