Cylindruria is a laboratory syndrome characterized by the detection of cylinders in the urine. Cylinders are proteinaceous formations that are casts of the distal tubules and collecting ducts. The cause of cylindruria is various kidney diseases and severe somatic conditions. These elements can be detected by microscopic examination of the urine sediment. To eliminate cylindruria, treatment of the underlying disease is necessary.
There are the following types of cylinders:
Almost all cylinders are pathological, except hyaline. Normally, they are formed from the Tamm-Horsfall protein secreted by the cells of the renal epithelium of the collecting ducts and distal tubules of the nephron.
The acidic environment of urine (pH below 5.3) promotes the polymerization of this protein, which leads to the formation of hyaline casts. In a small amount (physiological cylindruria), they can appear after severe emotional stress, intense physical activity, and taking diuretic drugs.
Types of casts in urine
A large number of hyaline casts are formed mainly from albumin that has entered the urine. Albuminuria indicates damage to the glomerular apparatus of the kidneys. Pathology is the detection of more than 2 cylinders in the analysis of urine according to the Nechiporenko method. This type of cylindruria is always accompanied by proteinuria.
Under microscopy, they look translucent, with a delicate homogeneous structure. Often they are extremely difficult to identify in an unstained urine sediment. Often there are hyaline cylinders with an overlay of cellular elements - leukocytes, erythrocytes, epithelial cells, etc. With concomitant liver diseases, the cylinders are stained with bilirubin in a bright yellow color.
In urine with a pronounced alkaline reaction (pH above 7.0) and a low relative density (below 1010), hyaline casts may not be detected at all even with severe proteinuria, since under these conditions they undergo dissolution. Diseases in which hyaline cylindruria is most common:
The product of cell degradation are granular casts. With the destruction of neutrophilic leukocytes, fine-grained cylinders are formed, with the decay of renal epithelial cells - coarse-grained. Their presence in the urine indicates a more severe course of the pathological process.
Granular cylinders are colorless, due to the presence of granules they have a clearer structure and an uneven, rough contour. They can be stained yellow with bilirubin and red-brown with hemoglobin. In some cases, they contain drops of fat (cholesterol). Granular casts are observed in the following diseases:
There are still discussions about the origin of this type of cylinder. It is assumed that they are the final stage of degradation of hyaline and granular casts during their long stay in the distal tubules and collecting ducts. In appearance, they resemble thawed wax, have sharply defined contours, characteristic “bay-like” impressions.
The structure can be homogeneous or granular. Typical cracks along the cylinder, broken or jagged edges. The width is much larger (2-6 times) than other cylinders, the size correlates with the severity of the process. Diseases and pathological conditions in which waxy cylinders are found:
As a result of fixation on the surface of the hyaline cylinders of erythrocytes, erythrocyte cylinders are formed. Erythrocytes can be dysmorphic (altered), dehemoglobinized, which is typical for glomerulonephritis of various etiologies (for example, IgA nephropathy), or unchanged, saturated with hemoglobin, which occurs with necrotizing vasculitis, kidney infarction, and acute interstitial nephritis.
Casts of the renal tubules, consisting of neutrophils, are leukocyte casts. The reason for their formation is a pronounced process in the kidneys, which is observed when:
When the epithelial cells of the tubules are detached, they can be fixed on hyaline casts, resulting in the formation of epithelial casts. It is often extremely difficult to differentiate an epithelial cylinder from a leukocyte cast in an unstained urine sediment smear. Basically, the cylinders are formed from fat-transformed epithelial cells. Etiological factors for the appearance of epithelial cylinders in the urine:
These casts are mainly formed from free hemoglobin that has entered the urine due to intravascular hemolysis (hemoglobinuria). Less commonly, they form when hemoglobin is released from red blood cells destroyed in the urine (hematuria). Hemoglobin casts are brown or red-brown in color and contain granules.
Sometimes they have to be differentiated from crystals of acidic ammonium urate. When 30% acetic acid is added, the crystals undergo dissolution, while the cylinders remain. Causes of the appearance of hemoglobin cylinders:
In acute kidney injury associated with severe muscle damage (prolonged compression syndrome), the myoglobin pigment released from necrotic muscle fibers first enters the blood, then into the urine, where myoglobin cylinders can form during its coagulation. They are small and reddish brown in color.
In some patients suffering from diseases accompanied by bilirubinuria (virtually all diseases of the liver and biliary tract), in some cases, bilirubin cylinders that have a yellowish or yellow-brown color are found in the urine.
When lipids and oval fat bodies are incorporated into the protein matrix, fat cylinders are formed. They are small in size, due to the large number of drops of fat sharply refract light. Often located on the background of fatty renal epithelium, cholesterol crystals and needles of fatty acids. The presence of fat casts is considered a characteristic feature of severe proteinuria. The reasons for their appearance are as follows:
The presence of cylinders in the urine (with the exception of a small number of hyaline cylinders) is a direct indication for contacting a general practitioner or nephrologist to find out the reasons for their appearance. At the appointment, the specialist asks the patient about the presence of complaints - fever, aching pain in the lower back. Anamnestic data are important. It is clarified whether the patient is taking medications, whether he is registered with a dispensary for a chronic disease.
A physical examination is carried out - examination of the skin for the presence of peripheral edema, checking the Pasternatsky symptom, measuring blood pressure. For the purpose of differential diagnosis and identification of the etiological factor of cylindruria, an additional examination is prescribed:
There are no independent methods for eliminating cylindruria. This requires treatment of the underlying disease. The first step in treatment is the appointment of a diet. Patients with diabetes are prescribed a low-carbohydrate diet. People with severe kidney disease should reduce their protein intake to 6g per day. In chronic heart failure, dietary salt intake is limited to 3 g / day. Of the drugs used are the following:
If cylindruria is detected, it is imperative to consult a doctor. Based on one cylindruria, only an approximate prognosis for the patient can be made. For example, the presence of only hyaline casts carries a better prognosis than the presence of wide, waxy casts. However, it is necessary to focus on other pathological elements of the urine sediment, as well as indicators of other laboratory and instrumental studies.