Urine protein is a common symptom of kidney disease. In normal case, there is only a small amount (150mg/d) in urine. However, once kidneys are injured, they will lose their normal barrier function, reabsorption function and so on. As a result, there will be a large amount of protein leak into urine. Clinically, it is named as proteinuria. The common causes of urine protein are as follows:
1. Urine protein caused by glomerular diseases
Urine protein in glomerular diseases is caused by the change of capillary permeability. Glomerular capillaries are composed of epithelial cells, basilar membrane and endothelial cells. The epithelial cells and endothelial cells have many holes that can permit the small molecular protein to leak, but stop the large molecular protein in blood. Moreover, glomerular basilar membrane is covered with laminin, collagen and other substances carrying negative charge. Therefore, the protein with negative charge will be prevented in blood and those with positive charge can pass. However, in glomerular diseases, the charge barrier and mechanical barrier functions are disordered so the protein will leak into urine.
2. Urine protein due to renal tubular injuries
(1) The resorption function of renal tubule is damaged. The some part of albumin, polypeptide and so on can pass glomeruli, but more than 95% of them will be reabsorbed by renal tubule. However, if the renal tubule is damaged, they will lose the normal resorption function. (2) In some cases of diseases, the renal tubule can secrete more protein like acute tubular necrosis, the rejection reaction caused by kidney transplant and so on.
3. Overflow proteinuria
In some cases of kidney diseases, excess protein is produced in blood and exceeds the reabsorption ability of renal tubule leading to urine protein.
The above three cases of urine protein are caused by pathological changes. Besides the above causes of urine protein, there are still some non-pathological causes of urine protein like intense exercises, fever, medicines and so on. However, in these cases, the urine protein only lasts for a short time and they do not need treatments. If you do not know the specific causes your urine protein and want get a clear answer, please consult us on line or email to khkpcn@hotmail.com.