Cylinders are structures formed exclusively in the kidneys that are not often identified in the urine of healthy people. Thus, when cylinders are observed in the urine test, it may be an indication that there is any change in the kidneys, be it infection, inflammation or destruction of kidney structures, for example.
The presence of cylinders is verified through urine examination, EAS or type I urine examination, where through microscopic analysis it is possible to observe the cylinders. Normally, when the presence of cylinders is verified, other aspects of the exam are also altered, such as leukocytes, number of epithelial cells and erythrocytes, for example. Here's how to understand the urine test.
How cylinders are formed
The cylinders are formed inside the distal contorted tubule and the collecting duct, which are structures related to the formation and elimination of urine. One of the main constituents of the cylinders is the Tamm-Horsfall protein, which is a protein excreted by the tubular renal epithelium and which is eliminated naturally in the urine.
When there is a greater elimination of proteins due to stress, extensive physical activity or kidney problems, proteins tend to stick together until a solid structure, the cylinders, is formed. Also during the formation process, it is possible that the elements present in the tubular filtrate (which later is called urine) are also incorporated, such as epithelial cells, bacteria, pigments, red blood cells and leukocytes, for example.
After the formation of cylinders, the constituent proteins detach themselves from the tubular epithelium and are eliminated in the urine.
Types of cylinders
The cylinders can be classified according to the place of formation and constituents, the main ones being:
- Hyaline: This type of cylinder is the most common and is basically formed by the protein Tamm-Horsfall. When up to 2 hyaline cylinders are found in the urine, it is normally considered normal, which can happen due to the practice of extensive physical activities, dehydration, excessive heat or stress. However, when several hyaline cylinders are seen, it can be indicative of glomerulonephritis, pyelonephritis or chronic kidney disease, for example; Hemic: This type of cylinder, in addition to the Tamm-Horsfall protein, is made up of red blood cells and is usually indicative of damage to any structure of the nephron, which is the functional unit of the kidneys responsible for the production of urine. It is common that in addition to the cylinders, in the urine examination it can indicate the presence of proteins and numerous red blood cells. In addition to being indicative of kidney problems, hematic cylinders can also appear in the urine test of healthy people after practicing contact sports; Leukocyte: It is formed mainly by leukocytes and its presence is usually indicative of infection or inflammation of the nephron, being generally associated with pyelonephritis and acute interstitial nephritis, which is a non-bacterial inflammation of the nephron. Although the leukocyte cylinder is indicative of pyelonephritis, the presence of this structure should not be considered a single diagnostic criterion, and it is important to evaluate other parameters of the examination; Bacterial: The bacterial cylinder is difficult to see, however it is common to appear in pyelonephritis and is formed by bacteria linked to the Tamm-Horsfall protein; Epithelial cells: The presence of epithelial cell cylinders in the urine is usually indicative of advanced destruction of the renal tubule, but it can also be associated with drug-induced toxicity, exposure to heavy metals and viral infections.
In addition to these, there are also granular, brain and fatty cylinders, the latter being formed by fat cells and is generally associated with nephrotic syndrome and diabetes mellitus. It is important that the result of the urine test is evaluated by the doctor, especially if the report indicates the presence of cylinders. Thus, the doctor can investigate the cause of the cylinder and start the most appropriate treatment.
