Additional methods of kidney examination

General clinical examination of the patient is supported by special, including instrumental, research methods that allow to detect primarily latent forms of kidney diseases, to assess the degree of activity of the process, anatomical features (primarily the size of the kidneys, which is important to know in case of a long-term disease, asymmetry of the size and shape of the kidneys, which may be caused by the presence of a cyst, tumor), as well as the state of the vascular system. Research methods that clarify the functional state of the kidneys occupy a key place.

Urine analysis. Urine analysis is of particular importance for diagnosing kidney diseases. Freshly released urine is normally transparent, straw-yellow in color (mainly due to urochromes). Diluted urine is light yellow, concentrated urine is yellow-brown. In chronic renal failure, the urine is very light (urochromes are not released). In conditions that cause increased protein breakdown (fever, hyperthyroidism, severe diseases - infections, tumors), as well as during pregnancy, urine can be dark brown. The color of urine can change if it contains blood, hemoglobin, and drugs. Thus, chloroquine, like acriquine, colors urine bright yellow; furadonin, furagin, rifampicin - orange; phenylin - pink; metronidazole (trichopolum) - dark brown. Cloudy urine can be due to a high content of salts, leukocytes, bacteria. With a large amount of urates, the urine sediment is orange-red, with phosphates it is brown-red.

The urine reaction is usually acidic. Alkaline urine is observed with a diet rich in fruits and vegetables, but poor in meat.

Excretion of protein in urine (albuminuria, or more correctly proteinuria) has been considered the most important sign of kidney damage since the time of R. Bright, although sometimes proteinuria occurs without kidney disease as such (fever, prolonged vertical position of the body - orthostatic proteinuria and walking - march proteinuria). Qualitative reactions for protein become positive at a protein concentration of 0.033 g / l. Quite accurate results in quantitative determination of protein are given by the method with sulfosalicylic acid (with mandatory preliminary filtration of urine) with determination of optical density on a photoelectrocolorimeter (PEC). The Roberts-Stolnikov method (with layering of urine on nitrous acid) is simpler, but not always reliable. The most accurate results are obtained using the biuret method.

Recently, much attention has been paid to the detection of microalbuminuria (albumin secretion from 25 to 200 μg/min) using immunochemical or radioimmune methods as a marker of early stages of kidney damage, when no other clinical or laboratory signs of the disease can yet be detected. Detection of microalbuminuria allows for the diagnosis of the earliest stages (essentially preclinical) of various kidney damage, such as diabetic nephropathy.

Of particular importance is the determination of daily proteinuria. It is believed that the release of protein more than 3.0-3.5 g per day, as a rule, quickly leads to a violation of the protein spectrum of the blood, which is especially characteristic of nephrotic syndrome.

Dynamic control of proteinuria level, especially daily proteinuria, is very important. Its increase, especially to the degree of nephrotic proteinuria (3.0-3.5 g/day and more), in the overwhelming majority of cases is an important sign of the activity of exacerbation of the chronic renal process. Likewise, a decrease in this indicator is, as a rule, an encouraging sign indicating the onset of spontaneous remission or the effectiveness of the pathogenetic treatment (glucocorticosteroids, cytostatics, etc.), with the exception of situations associated with the onset of chronic renal failure (in most cases, these are chronic kidney diseases: the development of chronic renal failure is accompanied by a decrease in proteinuria and the associated edema syndrome).

The qualitative characteristics of the protein excreted in the urine have a certain diagnostic value. The protein may be represented only by albumin, but more often large-molecular globulins, Tamm-Horsfall tubular protein, other tubular proteins, as well as myoglobin and hemoglobin are also excreted. It is very important to detect monoclonal proteins (paraproteins) in the urine, represented primarily by light chains of immunoglobulins excreted by the kidneys, for example, in myeloma, which can be detected using the Bence-Jones reaction, but even more reliably using electrophoresis, which allows us to establish the presence of an additional component in various fractions of the excreted globulins (usually in the gamma fraction) (for more information on proteinuria, see the description of nephrological syndromes).

Microscopic examination of urinary sediment can reveal erythrocytes, leukocytes, cylinders, and epithelial cells, and erythrocytes and leukocytes can enter the urine from any part of the urinary tract.

If more than 2 erythrocytes are found in the morning urine per microscope field of view, this is called erythrocyturia. Changed and unchanged erythrocytes are better determined by phase-contrast microscopy. Often, erythrocyturia (hematuria) prevails over leukocyturia, and sometimes over proteinuria.

In the urine of healthy people there may be up to 5 leukocytes in the field of view of the microscope, an increase in the number of leukocytes in the urine is called leukocyturia. With pronounced leukocyturia, the cells can form clusters. Pyuria is the macroscopically detectable presence of pus in the urine.

Morphological examination of leukocytes in urine, performed by microscopy of thin smears of urine sediment stained using the Romanovsky-Giemsa method, allows us to clarify the nature of leukocyturia and differentiate neutrophils (a sign of infectious inflammation) from lymphocytes (a marker of immune inflammation).

Cylindruria is associated with protein deposition in the lumen of the tubules. The protein base of the cylinders is Tamm-Horsfall uroprotein, produced by the epithelium of the convoluted renal tubules, as well as aggregated serum proteins. The cylinders can be purely protein (hyaline and waxy) and cellular (erythrocyte, leukocyte and epithelial cylinders). In granular cylinders, the protein base is covered with fragments of disintegrating cells.

The most frequently detected are hyaline casts, consisting of transparent homogeneous material without cellular components. Hyaline casts are also found in healthy people after physical exertion. They do not have much diagnostic value. The appearance of granular and waxy casts indicates serious damage to the renal parenchyma.

Quantitative methods, unlike general urine analysis, are standardized: the number of leukocytes is determined in a specific volume (in 1 ml of urine - according to Nechiporenko) or for a specific time (per day - the Kakovsky-Addis method, per minute - the Amburger method). In healthy individuals, 1 ml of urine contains up to 1000 erythrocytes and up to 2000 leukocytes (Nechiporenko method); per day, there are up to 1 million erythrocytes, leukocytes - up to 2 million (Kakovsky-Addis method).

Urine may contain squamous epithelial cells (polygonal) and renal epithelial cells (round), which are not always distinguishable by their morphological features. Urine sediment may also contain atypical epithelial cells, characteristic of urinary tract tumors.

Bacterioscopic examination of urine sediment is an indicative test that has some value only for identifying fungi, as well as for diagnosing tuberculosis of the urinary system (microscopy of smears from sediment with Ziehl-Neelsen staining).

Urine culture is of the utmost importance for quantitative assessment of the degree of bacteriuria (Gould's method). The presence of bacteriuria is indicated by detection of more than 100,000 bacteria in 1 ml of urine. Urine culture makes it possible to identify the type of pathogen and its sensitivity to antibacterial drugs. Special paper plates can be used for mass examinations of various contingents (dispensary examination, epidemiological studies). The methods that allow assessing the anatomical, morphological and functional state of the kidneys (size, shape of the renal pelvis, presence of cysts or tumors, vascular architecture, fine microscopic structure, a number of functional indicators) include X-ray, radiological, ultrasound examinations, kidney biopsy.

X-ray and radiological examination methods. A general image of the kidneys allows one to identify the size of the kidneys, their location and contours, as well as the shadows of stones.

With the help of intravenous (excretory) urography by introducing urotrast, verografin it is possible to contrast the shadows of the kidneys, the calyceal-pelvic system and the urinary tract, as well as to judge the functional state of the kidneys, their size and contours. Normally, the shadows of the kidneys are located in adults at the level of the XI thoracic - III lumbar vertebrae, the pelvis - at the level of the II lumbar vertebra. The right kidney is more mobile and is located slightly lower than the left. Usually the contours of the kidneys are smooth, the thickness of the parenchyma (the distance from the outer contour to the papillae of the pyramids) in the middle part of the kidneys (2.5 cm) is slightly less than at the poles (3-4 cm). A change in the contour of the kidney (tuberosity) can be caused by scars, tumor formations.

Hodson's sign (uneven thickness of the parenchyma: thinner at the poles compared to the middle part) is characteristic of chronic pyelonephritis. In healthy individuals, all calyces are equally contrasted.

Noticeable changes in the renal pelvis and calyces are most pronounced in chronic pyelonephritis, papillary necrosis, obstructive nephropathy, and renal tuberculosis.

The method of radioisotope renography is based on the property of the tubular epithelium of the kidneys to selectively extract ¹³¹ I-hippuran from the bloodstream with subsequent excretion in the urine. The accumulation and excretion of hippuran is recorded using scintillation sensors installed over the kidney area and is presented (summed up) in the form of two curves - renograms of the right and left kidneys. Important advantages of the method are separate assessment of the function of the right and left kidneys, comparison of curves and characterization of their symmetry. With the progression of nephropathy, the excretion of hippuran is increasingly impaired, the amplitude of the curves decreases, they stretch out and flatten.

Angiography is the production of a radiopaque image of the renal vascular system after the introduction of a contrast agent into the abdominal aorta through a catheter placed in the femoral artery (according to Seldinger), or less frequently translumbarly. In selective renal angiography, the radiopaque agent is introduced directly into the renal artery, which allows for a clearer image of the renal vessels. A series of images reveals the image of the renal arteries and their branches (arteriogram), then the shadow of the kidney (nephrogram), and finally the outflow of contrast fluid through the veins (venogram).

Ultrasound examination. Ultrasound scanning is a non-invasive method that allows determining the size and location of the kidney: indicated when there is a suspicion of a focal pathological process in the kidney (tumor, cyst, polycystic disease, abscess, tuberculosis, nephrolithiasis).

Kidney biopsy. Most often, a puncture percutaneous biopsy is performed with a special needle, less often - a semi-open biopsy (through a surgical incision) with a scalpel or needle. Kidney biopsy is used in nephrological practice to clarify the diagnosis of glomerulonephritis, amyloidosis (the latter can be less often proven by a biopsy of the submucosa of the rectum and gum).

According to the most widespread morphological classification in our country by V.V. Serov et al. (1978), the following variants of glomerulonephritis are distinguished:

1. proliferative (exudative-proliferative);
2. lipoid nephrosis (minimal changes);
3. membranous;
4. mesangial, including:
   • mesangiomembranous,
   • mesangioproliferative,
   • mesangiocapillary,
   • lobular;
5. extracapillary proliferative;
6. fibroplastic (as an option - focal segmental hyalinosis).

A kidney biopsy allows one of the indicated types of glomerulonephritis to be determined during life, and also helps in resolving issues of treatment and prognosis.

Contraindications to kidney biopsy include blood clotting disorders (bleeding tendency, thrombocytopenia, treatment with anticoagulants); inability of the patient to communicate (coma, psychosis); severe hypertension that does not respond to treatment; the presence of a single functioning kidney, shrunken kidneys.

Evaluation of the functional state of the kidneys. Determination of the functional state of the kidneys is the most important stage of the patient examination.

In everyday clinical practice, simple methods of quantitative assessment of renal functions are used - assessment of nitrogen excretion function (creatinine and urea content in serum, glomerular filtration rate), osmo- and ionoregulation functions. It is necessary to highlight two indicators of primary importance - determination of the creatinine level in the blood and the relative density of urine in a single analysis and in the Zimnitsky test.

The serum creatinine level clearly reflects the functional state of the kidneys. It should be emphasized that it is important to determine the serum creatinine content, rather than urea or the so-called residual (non-protein-bound) nitrogen, the level of which may increase even with preserved kidney function (increased catabolism during infections, tissue breakdown, steroid treatment, protein load). In addition, with a progressive decrease in kidney function, an increase in creatinine (normal 88-132 μmol/l) may significantly outpace the increase in urea content.

The most important functional test is the determination of the relative density of urine, the great clinical significance of which has long been highly appreciated. If the urine density is higher than 1.020 (and according to some authors, even higher than 1.018), other indicators of kidney function may not be determined in practice. If the relative density of morning urine portions does not exceed 1.018, further studies should be carried out.

The most common test was proposed by S.S. Zimnitsky, who described its physiological basis as follows: “Only concentration is actually purely renal work, this is in the full sense of the word renal function... Concentration determines for us the method and manner of renal work.”

Zimnitsky's test involves collecting eight 3-hour urine portions during voluntary urination and a water regime of no more than 1500 ml per day with determination of the relative density of urine in each of them. If in Zimnitsky's test the maximum value of the relative density of urine is 1.012 or less or there is a limitation of fluctuations in the relative density within 1.008-1.010, then this indicates a pronounced impairment of the concentration function of the kidneys. It is this condition of the kidney function that is called isosthenuria, which means the loss of the kidneys' ability to excrete urine of an osmolarity other than equal (from the Greek isos - equal) to the osmolarity of the protein-free plasma filtrate, i.e. the loss of the kidneys' ability to osmotic concentration of urine (the old term "asthenuria").

This state of decreased renal function usually corresponds to their irreversible wrinkling, which has always been considered to be characterized by the constant release of watery, colorless (pale) and odorless urine.

The small amplitude of the extreme values of the relative density of urine in the Zimnitsky test with fluctuations from 1.009 to 1.016 also indicates impaired renal function. In addition to fluctuations in the relative density of urine, the Zimnitsky test determines the ratio of daytime and nighttime diuresis. In a healthy person, daytime diuresis significantly exceeds nighttime diuresis and is 2/3 - 3/4 of the total amount of daily urine.

More subtle methods of assessing kidney function are based on the principle of clearance. Clearance (cleaning, depuration) is a conventional concept characterized by the rate of blood purification, it is determined by the volume of plasma that is completely cleared by the kidneys from a particular substance in 1 minute according to the formula:

Сх=Uх*V/Pх

Where Cx is the clearance; Ux and Px are the concentrations of the test substance (x-substance) in urine and plasma, respectively; V is the value of minute diuresis.

Determination of clearance in modern nephrology is the leading method for obtaining a quantitative characteristic of kidney activity - the value of glomerular filtration (GF). In the clinic, various substances (inulin, etc.) are used to characterize the GF value, but the most widely used method is the determination of endogenous creatinine clearance (Reberg test), which does not require additional introduction of a marker substance into the body. The method for determining endogenous creatinine clearance is given in modern nephrology manuals.

In recent years, much attention has been paid to the state of hyperfiltration - the extremely high value of the CF rate for a given individual, which is usually associated with the activation of the renal filtration reserves. It is believed that long-term hyperfiltration (CF> 150 ml/min) can lead to depletion of the renal filtration reserves (renal functional reserve), a kind of "wear and tear" of the organ, i.e. the inability of the kidney to increase the CF rate in response to various stimuli. Hyperfiltration is based on hemodynamic mechanisms - dilation of afferent arterioles with unchanged or increased tone of efferent arterioles, which creates a high intraglomerular hydrostatic pressure gradient. Persistent intraglomerular hypertension damages the glomerular basement membrane (GBM), which loses its negative charge and therefore becomes highly permeable to proteins (including albumin) that are deposited in the mesangium, leading to its expansion, proliferation, and ultimately focal and segmental hyalinosis and sclerosis. Early clinical signs of this renal condition are glomerular hyperfiltration and depletion of renal functional reserve. The appearance of microalbuminuria, preceding proteinuria, usually coincides with a decrease in renal functional reserve.

A number of effects (administration of dopamine, food protein loads) can lead to the appearance of hyperfiltration, which is used to assess the reserve functional capacity of the kidneys. For the same purpose, dry-eating tests (increase in the relative density of urine to 1.022-1.040 after 36 hours of deprivation - exclusion of fluid intake) and dilution tests (decrease in the relative density of urine to 1.001-1.002 during the first 4 hours after intake of 1.5 liters of water) are used.

A decrease in the rate of CF in pathological conditions can be associated with two reasons:

1. with hemodynamic disorders (hypovolemia, shock, dehydration, heart failure);
2. with organic changes in the kidneys (inflammation, sclerosis, other structural changes in the nephrons).

Thus, the value of creatinine clearance (CC) clearly corresponds to a certain level of serum creatinine, which is graphically well reflected by the characteristic curve. Therefore, in practice, the Reberg test can be replaced by determining the level of creatinine in the blood. However, in dynamic observation, especially during periods of exacerbation of renal disease, an important indicator is CC - successful treatment increases creatinine clearance. Recently, the dynamics of changes in a specific patient of the indicator, representing a value inverse to the value of blood creatinine, has attracted attention. Usually, with slowly progressing kidney damage, the graphic image of such dynamics corresponds to a flat line. If the direction (slope) of this line becomes steeper, one should assume the need for hemodialysis (or kidney transplantation) in the near future or exclude intercurrent causes of increasing renal failure (urinary tract infection, increased extracellular volume, urinary tract obstruction, exposure to nephrotoxins, uncontrolled arterial hypertension), which can accelerate the rate of development of chronic renal failure. At the same time, a decrease in the slope of the curve indicates a slowdown in the rate of disease progression and the success of the treatment.

Study of some biochemical and immunological parameters. In some cases, a study of the acid-base balance is carried out, to the maintenance of the stability of which the kidneys are directly related (determination of urine pH, titratable acidity of urine, excretion of bicarbonates, secretion of ammonia).

Biochemical determination of other homeostasis indices is of great clinical importance. Thus, hypoproteinemia (primarily hypoalbuminemia) indicates the presence of nephrotic syndrome, while a significant decrease in these indices (albumin level in the blood less than 1 g/l) is a sign of a serious condition of the patient due to the threat of hypovolemic shock (a sharp drop in the volume of circulating blood, followed by uncontrolled acute vascular insufficiency and arterial hypotension, oliguria). Biochemical confirmation of nephrotic syndrome is also hyperlipidemia (hypercholesterolemia).

Hyper-a2-globulinemia, as well as an increase in ESR, confirm the presence of an inflammatory process in kidney diseases, as evidenced by some immunological indicators. The latter may be important in clarifying the etiology of kidney disease (for example, detection of a high titer of antinuclear factor and "lupus" cells is more common in lupus nephritis; antibodies to the glomerular basement membrane of the kidneys - in Goodpasture's pulmonary-renal syndrome; antibodies to the cytoplasm of neutrophils (ANCA) - in nephritis associated with Wegener's granulomatosis; markers of the hepatitis B virus - in kidney damage due to viral hepatitis or cirrhosis of the liver). Studying the electrolyte composition of the blood is of great importance. Thus, hyperphosphatemia in combination with hypocalcemia is detected in the initial stage of chronic renal failure; Hyperkalemia is the most important indicator of severe renal failure; this indicator is often used as a guide when deciding whether to perform hemodialysis.

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