The sample in Zimnitskiy

Currently, the most common and affordable way to determine the function of the kidneys for breeding and concentrating urine is to determine the relative density of urine in a single analysis or in the Zimnitsky trial.

Relative density of urine is less sensitive than osmolality. Relative density of urine is influenced not only by osmotically active substances, but also by high molecular components (proteins, sugar, contrast substances) contained in the urine. To level out the significant differences between the indicators, when treating the relative density of urine, corrections were introduced for the content of protein and sugar in the urine. Thus, 1% of sugar in urine raises the relative density of urine by 0.004; 3 g of protein - by 0.001. Accordingly, at a protein concentration in urine of 10 g / L, the relative density is decreased by 0.003; at a glucose concentration of 10 g / l, by 0.0038. Determination of the relative density of urine is carried out no earlier than 3 days after the studies with the introduction of contrast agents and at least 3 days after taking diuretics.

In a healthy person, the relative density in the morning portion of urine, exceeding 1018, indicates the preserved ability of the kidneys to concentrate urine. The ability of the kidneys not only to concentrate, but also to dilute the urine is determined in Zimnitsky's trial. It consists in determining the relative density in eight portions of urine collected by the patient during the day with an interval of 3 hours. The sample is carried out at the usual physical activity of the patient, under the conditions of a standard drinking and food regime (allowed to drink about 1.2 liters of liquid per day) and not less than 3-5 days after the cancellation of diuretics.

In a healthy person, the daily urine output is 67-75% of the amount of fluid drunk; day diuresis - 65-80% of the amount of urine released per day. Oscillations of the relative density of urine in the norm of 1005-1025.

The following conditions characterize violations of volumo- and osmoregulatory functions of the kidneys on the basis of the Zimnitsky trial:

• oliguria, anuria - decrease in the amount of daily urine;
• polyuria - excess of the amount of excreted urine over the amount of liquid drunk;
• nocturia - increased diuresis at night;
• isostenuria - a change in the relative density of urine in the range 1010-1011, which corresponds to the value of the relative density of the blood plasma and reflects the completely impaired ability of the kidneys to concentrate and dilute urine;
• hypostenuria - relative density of urine in all portions below 1012, which reflects a violation of the concentrating ability of the kidneys;
• hypersthenuria - the relative density of urine in all portions exceeds 1010, which reflects a violation of the function of dilution of urine.

Reference urine (norm) in the study of Zimnitskiy:

• daily diuresis is 0.8-2 liters or 65-80% of the fluid drunk per day;
• significant fluctuation during a day of the amount of urine in individual portions (40-300 ml) and its density (1.008-1.025 g / l);
• day diuresis prevails over night (2: 1);
• the density of at least one portion is not lower than 1,020-1,022 g / l.

The trial according to Zimnitsky allows to study the concentration function of the kidneys. The patient remains in the normal diet, but takes into account the amount of liquid drunk. After emptying the bladder at 6 o'clock in the morning every 3 hours, urine is collected into separate jars within a day, only 8 servings. In the study of urine according to Zimnitsky, the main thing is to take into account density fluctuations in individual portions of urine. If it remains at a low level, despite interruptions in the intake of food and liquid, this indicates a disruption in the ability of the kidneys to concentrate urine. If the density remains at the usual level or its fluctuations do not exceed 0.007 g / l after fluid intake, this indicates a loss of ability to breed by the kidneys.