Additional methods of studying the kidneys

General clinical examination of the patient is supported by special, including instrumental, research methods that allow to detect primarily latent (latent) forms of kidney disease, to assess the degree of activity of the process, anatomical features (especially the size of the kidneys, which is important for a long-term disease, asymmetry size and shape of the kidneys, which can be due to the presence of cysts, tumors), as well as the state of the vascular system. The most important place is occupied by methods of research, specifying the functional state of the kidneys.

Examination of urine. Especially important for the diagnosis of kidney disease is the study of urine. Freshly released urine is normally clear, straw-yellow color (mainly due to urochromes). The diluted urine is light yellow, concentrated - yellow-brown. In chronic renal failure, urine is very light (urochromes are not secreted). In conditions that cause increased protein breakdown (fever, hyperthyroidism, severe diseases - infections, tumors), and also during pregnancy, urine may be of a dark brown color. The color of urine can vary with the content of blood, hemoglobin, drugs. So, chloroquine, like acrichine, stains urine in a bright yellow color; furadonin, furagin, rifampicin - in orange; phenylin - in pink; Metronidazole (Trichopolum) - in dark brown. Urine clouding can be a consequence of the high content of salts, leukocytes, bacteria. With a large amount of urate, the urine sediment is orange-red, the phosphate is brownish-red.

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

Excretion of protein with urine (albuminuria, more correctly proteinuria) since R. Bright is considered the most important sign of kidney damage, although sometimes proteinuria also occurs without kidney disease per se (fever, prolonged vertical position of the body - orthostatic proteinuria and walking - march proteinuria). Qualitative reactions to the protein become positive at a protein concentration of 0.033 g / l. Precisely accurate results in the quantitative determination of protein gives a method with sulfosalicylic acid (with mandatory pre-filtering of urine) with the determination of the optical density on a photoelectrocolorimeter (FEC). The Roberts-Stol'nikov method (with urine layering 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 identification of microalbuminuria (release of albumin from 25 to 200 mg / min) using immunochemical or radioimmune methods as a marker of early stages of kidney damage, when no other clinical and laboratory signs of the disease can be detected. The detection of microalbuminuria allows one to diagnose the earliest stages (essentially preclinical) of various kidney lesions, such as diabetic nephropathy.

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

Dynamic control over the level of proteinuria, first of all daily, is very important. Accumulation of it, especially to the degree of nephrotic proteinuria (3.0-3.5 g / day or more), in the vast majority of cases is an important sign of activity of exacerbation of the chronic renal process. Likewise, a decrease in this indicator, usually an encouraging sign, indicating the onset of spontaneous remission or the effectiveness of the pathogenetic treatment (glucocorticosteroids, cytostatics, etc.), the exceptions are situations associated with the onset of chronic renal failure (in most cases they are chronic kidney disease: the development of chronic renal failure is accompanied by a decrease in proteinuria and related edematous syndrome).

A definite diagnostic value is the qualitative characteristic of the protein excreted in the urine. The protein can be represented only by albumin, but also large-scale globulins, the tubular protein of Tamm-Horsfall, other tubular proteins, and also myoglobin and hemoglobin are also prominent. It is very important to identify in the urine monoclonal proteins (paraproteins), represented primarily by light chains of immunoglobulins released by the kidneys, for example in myeloma, which can be detected with the help of the Bence-Jones reaction, but even more reliably by electrophoresis, which makes it possible to ascertain the presence of an additional component in various fractions of isolated globulins (more often in gamma fraction) (for more details about proteinuria, see the description of nephrologic syndromes).

When microscopic examination of urinary sediment can be detected erythrocytes, white blood cells, cylinders, epithelial cells, while erythrocytes and white blood cells can enter the urine from any part of the urinary tract.

If more than 2 erythrocytes are found in the morning urine in the field of view of the microscope, they speak of erythrocyturia. Changed and unchanged erythrocytes are better determined by the method of phase contrast microscopy. Often erythrocyturia (hematuria) predominates over leukocyturia, and sometimes over proteinuria.

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

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

Cilindrarium is associated with the precipitation of protein in the lumen of the tubules. The protein base of the cylinders is the Tamm-Horsfall uroprotein, produced by the epithelium of the convoluted renal tubules, and also the aggregated serum proteins. Cylinders can be pure protein (hyaline and waxy) and cellular (erythrocyte, leukocyte and epithelial cylinders). In granular cylinders, the protein base is covered with fragments of decaying cells.

The most often found are hyaline cylinders, consisting of a transparent homogeneous material without cellular components. Hyaline cylinders are also found in healthy people after exercise. They have no great diagnostic value. The appearance of granular and waxy cylinders indicates a serious lesion of the renal parenchyma.

Quantitative methods, in contrast to the general analysis of urine, 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 (for a day - the method of Kakovsky-Addis, per minute - the method of Ambjurge). In healthy individuals, 1 ml of urine contains up to 1000 erythrocytes and up to 2000 leukocytes (Nechiporenko method); for a day there are up to 1 million erythrocytes, leukocytes - up to 2 million (Kakovsky-Addis method).

In the urine, flat epithelial cells (polygonal) and renal epithelium (round) can be detected, not always distinguishable by their morphological features. In the urine sediment, atypical epithelial cells characteristic of tumors of the urinary tract can also be detected.

Bacteriologic examination of urine sediment is an orientation test, which has definite value only for the detection of fungi, as well as for the diagnosis of urinary tuberculosis (microscopy of smears from sediment with Tsiol-Nielsen staining).

The most important is the culture of urine for the quantification of the degree of bacteriuria (Gould method). The presence of bacteriuria is indicated when more than 100,000 bacteria are detected in 1 ml of urine. Sowing urine makes it possible to identify the type of pathogen, its sensitivity to antibacterial drugs. When mass surveys of different contingents (clinical examination, epidemiological studies), special paper plates can be used. Methods to assess the anatomo-morphological and functional state of the kidneys (size, shape of the bowl-and-pelvis system, the presence of cysts or tumor formations, vascular architectonics, a fine microscopic structure, a number of functional indicators) include X-ray, radiological, ultrasound, kidney biopsy.

X-ray and radiological methods of research. A review of the kidneys can reveal the size of the kidneys, their location and contours, as well as shadows of the stones.

With the help of intravenous (excretory) urography, by introducing urotrast, verovraphin succeeds in contrasting the shadows of the kidneys, the bowl-and-pelvic system and the urinary tract, as well as judging 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, pelvis - at level II of the lumbar vertebra. The right kidney is more mobile and is located somewhat lower left. Usually the contours of the kidneys are even, the thickness of the parenchyma (distance from the outer contour to the papillae) in the middle part of the kidneys (2.5 cm) is somewhat smaller than at the poles (3-4 cm). The change in the contour of the kidney (tuberosity) may be due to scars, tumor formations.

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

Noticeable changes in the calyx and pelvic system are most pronounced in chronic pyelonephritis, papillary necrosis, obstructive nephropathy, tuberculosis of the kidneys.

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 blood stream followed by excretion by urine. Accumulation and isolation of hippuran is recorded using scintillation sensors installed above the kidney region and is (summarized) in the form of two curves - the renograms of the right and left kidneys. Important advantages of the method are a separate evaluation of the function of the right and left kidneys, the comparison of curves and the characteristic of their symmetry. With the progression of nephropathy, the excision of hippuran is increasingly disrupted, the amplitude of the curves decreases, they are stretched and flattened.

Angiography is the preparation of a radiopaque image of the vascular system of the kidneys after the administration of a contrast agent (a substance into the abdominal aorta through a catheter placed in the femoral artery (according to Seldinger), or less frequently transluminally. With selective renal angiography, the radiopaque substance is injected directly into the renal artery, which allows for a clearer image vessels of the kidney.The series of images reveals the image of the renal arteries and their branches (arteriogram), then the shadow of the kidney (nephrogram) and, finally, Otto contrast fluid through the veins (venograms).

Ultrasonography. Ultrasound scanning is a non-invasive method that allows to determine the size and location of the kidney: it is indicated if there is a suspicion of a focal pathological process in the kidney (tumor, cyst, polycystosis, abscess, tuberculosis, nephrolithiasis).

A biopsy of the kidney. More often, puncture percutaneous biopsy with a special needle is performed, rarely a half-open biopsy (through the surgical incision) with a scalpel or needle. Kidney biopsy is used in nephrological practice to clarify the diagnosis of glomerulonephritis, amyloidosis (the latter less often can be proved by biopsy of the submucosal membrane of the rectum and gum).

According to the most common morphological classification in our country, V. V. Serov et al. (1978) distinguish the following variants of glomerulonephritis:

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

A kidney biopsy allows one to determine one of these types of glomerulonephritis during life, and also helps in solving the problems of treatment, prognosis.

Contraindications to kidney biopsy are violations of blood clotting (tendency to bleeding, thrombocytopenia, treatment with anticoagulants); inability of the patient to come into contact (coma, psychosis); severe hypertension, not amenable to treatment; presence of a single functioning kidney, wrinkled kidneys.

Assessment of the functional state of the kidneys. Determining the functional state of the kidneys is the most important stage in the examination of the patient.

In everyday clinical practice, simple methods for the quantitative evaluation of renal functions are used-the evaluation of the nitrogen excretory function (serum creatinine and urea content, glomerular filtration rate), osmo- and ionoregulation functions. It should be noted two indicators that are of paramount importance - the determination of the level of creatinine in the blood and the relative density of urine in a single analysis and in the Zimnitsky trial.

The level of serum creatinine clearly reflects the functional state of the kidneys. It should be emphasized the importance of determining the content of creatinine in the blood serum, and not urea or the so-called residual (non-protein bound) nitrogen, whose level can also increase with preserved kidney function (increased catabolism in infections, tissue decay, steroid treatment, protein load). In addition, with an increasing decrease in renal function, an increase in the level of creatinine (norm of 88-132 μmol / l) can significantly outstrip the increase in the 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), in the practice of other indicators of kidney function can not be determined. If the relative density of morning portions of urine does not exceed 1.018, further research should be carried out.

The most common is the sample, proposed by SS Zimnitsky, who described her physiological basis: "Only concentration is actually a purely renal work, this is in full sense a renal function ... Concentration determines the way and method of kidney work for us."

Zimnitsky's sample includes the collection of eight 3-hour portions of urine with an arbitrary urination and an aqueous regimen of no more than 1500 ml per day with the determination of the relative density of urine in each of them. If in the Zimnitsky trial the maximum value of the relative density of urine is 1.012 or less or there is a restriction of the relative density fluctuations within 1.008-1.010, this indicates a marked violation of the concentration function of the kidneys. It is this state of renal function that has been termed isostenuria, which means that the kidneys lose the ability to excrete urine from other osmolality, except for the equal (from Greek isos-equal) osmolality of protein-free plasma filtrate, ie, kidney loss of ability to osmotic urine concentration (old term " astenuria ").

This state of the decline in kidney function usually corresponds to irreversible their wrinkling, for which it has always been considered characteristic to permanently excrete a watery, colorless (pale) and odorless urine.

The small amplitude of the extreme values of the relative density of urine in the Zimnitsky trial with oscillations from 1.009 to 1.016 also indicates a violation of kidney function. In addition to fluctuations in the relative density of urine, the ratio of day and night diuresis is determined in Zimnitsky's trial. In a healthy person, daytime diuresis is significantly greater than nighttime diuresis and is 2/3 -3/4 of the total daily urine.

More subtle methods for assessing kidney function are based on the use of the principle of clearance. Clearance (purification, depilation) is a conditional concept characterized by the rate of purification of the blood, it is determined by the volume of the plasma, which is completely purified by the kidneys from this or that substance in 1 min by the formula:

Cx = Ux * V / Px

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

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

In recent years, much attention has been paid to the state of hyperfiltration - an extremely high value of the rate of CF for a given individual, which is usually associated with the connection of the filtration reserves of the kidney. It is believed that prolonged hyperfiltration (CF> 150 ml / min) can lead to depletion of the filtration reserves of the kidneys (renal functional reserve), a peculiar "wear" of the organ, i.e., the inability of the kidney to increase the rate of CF in response to various stimuli. Hyperfiltration is based on hemodynamic mechanisms - dilatation of afferent arterioles with an unchanged or increased tone of the outgoing arterioles, which creates a high intra-lapse gradient of hydrostatic pressure. Persistent intramural hypertension damages the basal membrane of the glomeruli (BMC), which loses its negative charge, and therefore becomes highly permeable for proteins (including albumin), which are deposited in mesangium, which leads to its expansion, proliferation, ultimately - focal and segmental hyalinosis and sclerosis. Early clinical signs of this state of the kidneys are glomerular hyperfiltration and depletion of the renal functional reserve. The appearance of microalbuminuria, preceded by proteinuria, usually coincides with a decrease in the renal functional reserve.

A number of effects (dopamine administration, food protein loads) can lead to the appearance of hyperfiltration, which is used to assess the reserve functionality of the kidneys. For the same purpose, samples with dryness are used (increasing the relative density of urine to 1,022-1,040 after 36 hours of deprivation - excluding the use of liquid) and dilution (decrease of the relative density of urine to 1,001-1,002 within the first 4 hours after intake of 1.5 liters of water) .

Reduction in the rate of CF in pathological conditions can be due to two reasons:

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

So, the magnitude of creatinine clearance (CF) clearly corresponds to a certain level of serum creatinine, which graphically well reflects the characteristic curve. Therefore, in practice, Reberg's test can be replaced by determining the level of creatinine in the blood. However, with dynamic observation, especially during periods of exacerbations of kidney disease, an important indicator is CF - successful treatment increases the clearance of creatinine. Recently, attention has been drawn to the dynamics of changes in a particular patient, a measure that is the reciprocal of the value of creatinine in the blood. Usually, with slowly progressing kidney damage, the graphic image of such dynamics corresponds to a shallow line. If the direction (slope) of this line becomes steeper, it is necessary to assume the necessity of hemodialysis (or kidney transplantation) in the near future or to exclude the intercurrent causes of increasing renal failure (urinary tract infection, increased extracellular volume, urinary tract obstruction, nephrotoxicity, 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.

Research of some biochemical and immunological parameters. In a number of cases, the acid-base state is studied, to maintain the stability of which the kidneys have a direct relationship (pH of urine, titrated acidity of urine, excretion of bicarbonates, ammonia secretion).

The biochemical determination of other parameters of homeostasis is of great clinical importance. Thus, hypoproteinemia (primarily hypoalbuminemia) indicates the presence of a nephrotic syndrome, while a significant decrease in these parameters (albumin level in the blood of less than 1 g / l) is a sign of a patient's severe condition due to the threat of hypovolemic shock (a sharp drop in the volume of circulating blood, the following 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 diseases of the kidneys, 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 the antinuclear factor and "lupus" cells is more common in lupus nephritis: antibodies to the basal membrane of the glomerulus of the kidneys - with pulmonary kidney syndrome Goodpasture, antibodies to the cytoplasm of neutrophils (ANCA, ANCA ) - with nephritis associated with Wegener's granulomatosis, hepatitis B virus markers - with kidney damage due to viral hepatitis or liver cirrhosis. It is important to study the electrolyte composition of the blood. Thus, hyperphosphataemia in combination with hypocalcemia is found in the initial stage of chronic renal failure; hyperkalemia is the most important indicator of severe renal failure, often this indicator is guided when deciding whether to conduct hemodialysis.

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