What causes high protein in children's urine?

Many people are worried about the health of their children, but worrying alone may not be of any use. We still have to take care of our children in every aspect of life. Sometimes we see high urine protein in children, but we don’t know what caused this. So what is the reason for high urine protein in children? Let’s see how the editor answers this question.

In fact, urine is a "mirror" of the health of kidney function. A routine urine test can directly reflect the functional status of the kidneys. When a healthy person undergoes a routine urine test, the urine protein (urine occult blood) index usually shows a negative result. If the test results show that the urine protein is positive, ranging from +, 2+, to 3+, it means that there must be a lesion in the kidney.

The occurrence of proteinuria is mainly related to glomerular filtration and tubular reabsorption. Under normal circumstances, the glomerular basement membrane can prevent high molecular weight proteins (molecular weight > 150,000, such as IgM) from passing through. The epithelial cell membrane fissure can prevent the passage of medium-molecular proteins (molecular weight between 50,000 and 150,000, such as albumin and transferrin); it also has a barrier effect on low-molecular proteins. The leaked low-molecular-weight proteins are often reabsorbed or broken down by the glomerular tubules. In normal children, 99% of the protein filtered by the glomerulus is reabsorbed in the distal part of the proximal tubule. When the glomerular filtration function and tubular reabsorption function are impaired, proteinuria may occur.

(a) Increased glomerular filtration

1. Increased permeability of the glomerular basement membrane (filtration membrane): When glomerular disease occurs, the immune complexes produced by the antigen-body reaction are deposited on the basement membrane, activating the complement, which damages the glomerular basement membrane and enlarges the pores. At this time, not only does the filtration of albumin increase, but large molecular globulins also leak out. When the filtration exceeds the limit of tubular reabsorption capacity (3000 mg/L), glomerular proteinuria occurs. Leakage of only albumin and small molecular weight proteins (molecular weight ≤ 150,000) is called selective proteinuria, while leakage of large molecular weight globulins (molecular weight > 150,000) is called non-selective proteinuria.

2. The electrostatic screen effect of the glomerular filtration membrane is weakened: The micropore wall of the glomerular filtration membrane normally carries a negative charge (such as sialoprotein polyanions), and the repulsive effect between it and the electrostatically charged protein molecules constitutes the effect of restricting the filtration of protein molecules. When glomerular disease occurs, the fixed negative charge on the glomerular capillary wall decreases, weakening the electrostatic screening effect of the filtration membrane, allowing medium-sized multivalent anions in the blood, such as albumin, to pass through the filtration membrane and enter the glomerular cavity, exceeding the glomerular reabsorption capacity and forming proteinuria.

3. In certain kidney diseases, renal hemodynamics changes, such as a decrease in renal blood flow and redistribution of blood within the glomeruli, which increases the protein concentration and osmotic pressure in the glomerular capillaries, or increases the effective filtration area, all of which can increase the filtration of plasma proteinuria through the glomeruli.

(ii) Reduced reabsorption of protein by the renal tubules

The renal tubules have a strong absorption capacity for proteins filtered through the renal tubules and can reabsorb almost all of the low-molecular-weight proteins in the filtrate. When there is a congenital enzyme metabolic defect or an acquired lesion, renal tubular dysfunction occurs, and low-molecular-weight proteins that are normally filtered by the glomerulus cannot be reabsorbed, resulting in glomerular proteinuria.

Through the above contents, we have understood the specific content of high urine protein in children. In addition to these contents, we must also better protect the health of children. The healthy growth of a child is the greatest happiness and wish of every parent, so if your child has proteinuria, you must go to the hospital for a regular examination to avoid delaying the treatment of your child's illness. Finally, I wish all the children can grow up healthy and happy!