Diagnosis of concentration function of kidneys

Description:

For assessment of concentration function of kidneys  use a number of methods:
1. Determination of relative density and osmolality of urine.
Relative density is defined by amount of solutes in urine. The relative density of urine is influenced by character of food, amount of the drunk liquid, expressiveness of extrarenal losses, character of the particles (protein, sugar) dissolved in urine. Normal in usual conditions relative density makes 1008–1025 g/l.
Osmolality of urine is more strict indicator to a lesser extent depending on character of the dissolved particles. Osmolality and relative density are closely connected among themselves. Ispolyyozovaniye of units of osmolality gives the chance of comparison of urine and blood.
2. Zimnitsky's test. The research is conducted in the conditions of free reception of liquid against the background of a physiological table. During the day each 3 hours collect urine in separate banks, measure its quantity and determine relative density. For the same temporary intervals consider the volume of the drunk liquid. Test should be estimated taking into account possible extrarenal losses.
Reyzelman's test – modification of test of Zimnitsyoky according to which collecting urine is carried out through free intervals of time. It is used at children's age.
At the kept ability of kidneys to osmotic cultivation and concoction of urine are noted:
– considerable fluctuations of volume of urine in separate portions (50–250 ml);
– the maximum relative density characterizing ability of kidneys to concentrate urine has to be not lower than 1025 g/l;
– the healthy person has to have minimum relative density reflecting ability of kidneys to osmotic cultivation of urine below osmotic concentration (osmolality) of the protein-free plasma equal 1010–1012, and usually makes 1003–1006;
– considerable fluctuations of relative density of urine: the difference between the maximum and minimum indicators has to make not less than 12-16 units (for example from 1006 to 1020 or from 1010 to 1026 etc.); considerable daily fluctuations of relative density of urine are connected with the kept ability of kidneys to concentrate, to dissolve urine depending on constantly changing requirements of an organism;
– clear (approximately double) dominance of a day diuresis over night.
3. Loading tests. Test on concoction.
Investigated is in the xerophagia mode within 12–24 hours. Water, fruit, berries, vegetables are excluded from a diet, friable porridges, crackers, hard-boiled egg, cottage cheese, meat join. The research begins at 15:00, empty a bladder then urine gathers each 3 hours, the amount of urine, relative density or osmolality is defined. Time of the end of test is determined by a measure of obtaining results (achievement of level of specific density of 1025 g/l and above), and also taking into account health of the patient.
Contraindications to conducting test:
• children of early age
• diseases of the central nervous system
• activity of inflammatory process in kidneys
• renal failure
• exchange nephropathy (including neuroarthritic diathesis).
Decrease in osmotic pressure in fabric of a medulla of kidneys is the cornerstone of disturbance of concentration ability of kidneys. It can be caused both by damage of kidneys, and extrarenal factors.
When progressing diseases of kidneys decrease in concentration ability is combined with disturbance of ability of kidneys to cultivation.
4. Loading tests. Water test.
During the research food is not given, the patient is on a semi-bed rest. Use boiled water of the room temperature of 20 ml/kg which is drunk within 15–30 minutes. Then the bladder is emptied, and urine is collected by each 30 minutes within two hours (4 portions) and within 1–2 hours in an hour (1–2 portions). For receiving the continued maximum diuresis at the beginning of each next collecting urine to the child allow to drink the amount of water equal to volume of the received urine for the previous period plus an amount of water on extrarenal losses.
Contraindications to conducting test:
• edematous syndrome
• gipertenzionny syndrome
• heart failure
• the states which are followed by tachycardia.

Interpretation of results:
– the healthy child in the first two hours allocates not less than 70% of the drunk liquid, the relative density of urine at the same time decreases (to 1001–1005 g/l);
– at decline in the ability of kidneys to cultivation of urine of value of relative density do not reach these indicators (usually 1004 - 1009 g/l);
– at full loss of function of cultivation relative density is at the level of 1010–1012 g/l, i.e. corresponds to osmotic concentration of plasma (isosthenuria).
The oliguria caused by a renal failure in most cases is combined with decrease in osmolality of urine (or specific density). Oliguyoriya at patients with the kept function of kidneys is followed by department of urine with the normal or increased specific density (tab. 3).
Load tests allow to estimate a functional condition of kidneys and their reserve opportunities, but existence of a number of contraindications (including early children's age) their use limits.
Now for assessment of concentration function of kidneys desmopressin is used (a synthetic analog of natural antidiuretic hormone arginine-vasopressin). In comparison with natural hormone, desmopressin possesses more powerful and prologirovanny action and does not render the expressed vasoconstrictive effect.
One of dosage forms of desmopressin is drug of Presayneks – spray nasal dosed. According to results of foreign multicenter researches drug differs in high precision of a dosage, a convenient form of release, safe and efficiently uses, does not cause a nose mucosal atrophy.
Presayneks's doses for test for concentration ability of kidneys depend on age:
Average dose
Adult – 40 mkg/days
Children about one year – 10 mkg/days
Children are more senior than year – 10–20 mkg/days
Test for concentration ability of kidneys with Presayneks's use provides consecutive performance of the following conditions:
• To enter spray in the dose recommended for test.
• To empty a bladder (the first portion is poured out). To carry out a repeated intake of urine in 4 hours after the first bladder emptying.
• One more intake of urine — in 4 hours.
• For definition of osmolality only two portions of urine within 8 hours gather.
• During the research to limit amount of the accepted liquid (the volume of the liquid which arrived in 1 hour prior to a research and within 8 hours later should not exceed 0,5 liters).
The received results estimate on osmolality indicators.
• Standard of osmolality for adults — till 1200 ¼Äß¼/kg H2O.
• Children have a standard of osmolality – 600 ¼Äß¼/kg H2O (has to reach within 5 hours after administration of drug).
• If the revealed indicator of osmolality is lower than the specified values, then the test needs to be repeated. Repeated identification of a low indicator demonstrates disturbance of concentration ability of kidneys. In this case the patient needs additional profound inspection.
Thus, Presayneks's use is a new noninvasive diagnostic method of disturbances of concentration function of kidneys, including at children of early age.