Blood osmolarity: concept, norms in tests, what changes in values ​​indicate

Osmolarity of blood and urine

Definition

• Osmosis is the one-way movement of a solvent (water) through a semi-permeable membrane, separating two solutions with different concentrations of solutes (osmotically active substances), towards a solution with a high concentration.
• Osmotically active substances are sodium ions (Na+), chloride (CL-) and bicarbonate (HCO3-), as well as glucose, urea, and proteins.
• Sodium, potassium and glucose cannot diffuse (pass) through the cell membrane, therefore, with pathological changes in their concentrations, a significant change in blood osmolarity and associated complications occur.
• Substances such as urea and ethanol diffuse freely through the cell membrane and therefore do not have a significant effect on blood osmolarity.
• Osmolarity – osmotically active substances dissolved in 1 liter of solution (water). The unit of measurement is milliosmol per liter (mOsm/L).
• Osmolality is the concentration of the same particles dissolved in a kilogram of water. The unit of measurement is milliosmole per kilogram of solution (mOsm/kg).
• Blood and urine osmolarity can be measured using instruments or can be calculated using a mathematical formula (theoretical osmolarity).
• Osmotic window is the difference between actual (measured) and theoretical osmolarity (see below). To calculate theoretical osmolarity, it is necessary to take tests for sodium, potassium, glucose and urea in the blood.

Indication

• Diagnosis of hyponatremia (low sodium) or hypernatremia (high sodium).
• Diagnosis of diabetes insipidus or primary polyuria (large volume of urine).
• Determination of the osmotic window is used to assess the presence of osmotically active substances that are not taken into account in the formula for calculating theoretical osmolarity (see below), for example, in toxicology. Osmotically active substances are also: ethanol, methanol, ethylene glycol, isopropanol, dichloromethane, lactate, ketone bodies, etc.
• Urine osmolarity is also used to diagnose hypo- or hypernatremia.

Methods (osmometers of various modifications)

• Freezing point depression method (the higher the osmolarity, the lower the freezing point of the solution).
• Method of increasing the boiling point (the higher the osmolarity, the higher the boiling point).

Reference values ​​(normal limits)

• Units of measurement are mOsm/l = mOsm/kg.
• Reference values ​​taken from Thomas L. Labor und Diagnose 2012.

The indicated limits of the norm may differ from those of your laboratory. Therefore, be guided by the norms indicated on the analysis form.
d = days after birth; m. = month; l. = years

Determination of the osmotic window

• Serum osmolarity (OSM) can be calculated using the following formula. Theoretical TMR in blood = 1.86 x sodium (mmol/l) + glucose (mmol/l) + urea (mmol/l) + 9.
• Blood osmotic window (mOsm/kg) = actual OSM (measured using instruments) minus theoretical OSM. For example, osmotic window = 285-282 = 3 mOsm/kg.

Interpretation of blood osmolarity (BOS) results

• TSC changes in parallel with the concentration of sodium in the blood. The interpretation depends on hyponatremia or hypernatremia.
• An increase in blood osmolarity >290 mOsm/kg activates the feeling of thirst due to the secretion of antidiuretic hormone.
• An increased TSC of 40-60 mOsm/kg due to loss of water or due to an increase in sodium or glucose can lead to cerebral edema and death.
• Decreased blood osmolarity
• Osmotic window >6-
• >10 mOsm/kg - poisoning with ethanol, methanol or other substances.
• In severe bleeding, the osmotic window is >15 mOsm/kg without detecting any osmotically active substances.

Deviations from the norm

The blood osmolality test is of important diagnostic value, for example, in diabetes mellitus, since in this disease the osmolality of the blood usually increases.
In addition, such an analysis, which actually monitors the state of the blood plasma, can help select more accurate and successful treatment. Serum osmolality analysis is also performed to assess the level of sodium, urea, and glucose. Urea is one of the breakdown products of protein in the body. The osmolality test helps assess the water-salt balance of the patient's body. A doctor may order this blood test if he or she suspects that a patient is developing one of the following conditions:

• dehydration, dehydration,
• deficiency of sodium in the blood - hyponatremia,
• renal failure,
• poisoning with ethanol, ethylene glycol, methanol.

Blood is drawn from a vein, in the morning, on an empty stomach. Before taking the test, it is recommended not to eat for 6 hours, and not to drink any liquids other than clean water.

The normal values ​​of osmolarity of biological fluids such as blood, or rather its serum (plasma), as well as cerebrospinal fluid (CSF), differ little, which cannot be said about urine, in which the norms for this parameter are 2 to 4 times higher.

Biological environmentNormal limits

Numerical indicators of blood osmolarity in children, although not as significant, are still different from those in adults (Table 2). OSK (norm) in children begins to change starting from 9 months of age. By the age of one year it reaches 280 - 300 mOsm/l (the norm for an adult), remaining within these limits, regardless of the person’s age, until the end of life.

Child's ageNormal, mosm/l

It should be noted that the above standards for adults and children may differ from those in other laboratories. In this regard, patients should first of all focus on the limits of normal values ​​indicated in the analysis form of a particular laboratory.

The study of oncotic and osmotic pressure of blood plasma is very important for the examination and treatment of patients suffering from diabetes. This is explained by the fact that this disease is characterized by an excess of the osmolarity norm, so if several tests do not show a decrease in this indicator, the specialist should prescribe the patient another treatment.

The study of serum osmolarity is carried out in order to find out the quantitative indicator of urea, glucose and sodium. Urea is the result of protein breakdown in our body. The study of osmolality allows doctors to understand the state of water-salt balance in the body of the person being studied.

Dehydration

• Lack of sodium.
• Kidney failure.
• Poisoning from chemicals or gases.

Generally accepted medical standards for serum osmolality

The formula is very simple: Osm = 1.86 Pa G M 10.

PA is a quantitative indicator of sodium.

G – glucose concentration.

M – urea index.

After conducting a series of studies, the laboratory issues a transcript that contains several indicators:

1. Blood plasma osmolarity - normally this indicator varies from 280 to 300 mOsm/L.
2. Urine osmolality – normal values ​​are considered to be 50-1200 mOsm/kg.
3. Osmotic window is the difference between the actual and theoretical osmolarity. Normally it does not exceed 6 mOsm/kg.

For convenience, the decoding is presented in the form of a table, where all the above indicators are entered and compared with the norm. The last column may indicate probable causes of deviations from the norms.

In addition to osmolarity, there is such an indicator as osmolality. It records the number of dissolved particles in the blood plasma indicated per 1 kg of blood. It is calculated using the following formula:

• Osm = 1.86 Pa G M 10, where
• Pa – sodium index;
• G – glucose;
• M – urea.

The normal value varies from 274 to 296 mOsm/kg of water.

In the case when there is an excess or deficiency of certain microelements in the blood plasma, we are talking about the presence of deviations. In this case, they can be of two types: hyperosmolarity and hypoosmolarity. Let's look at these states in more detail.

Hyperosmolarity, in which the normal level is exceeded, can develop in the following cases:

1. Prolonged dehydration of various etiologies, including pathologies of absorption of liquids in the intestine.
2. Bruises and mechanical damage to the membranes of the brain, which causes disruption of the hypothalamus.
3. High blood glucose levels caused by poor diet and insufficient insulin synthesis.
4. Rapid increase in sodium in blood plasma.
5. Kidney diseases, in which harmful substances are not completely eliminated from the body.
6. Intoxication with toxic substances, including food poisoning.
7. Stroke of cerebral vessels, in which the normal nutrition of cells is disrupted.

Dehydration

The study of oncotic and osmotic pressure of blood plasma is very important for the examination and treatment of patients suffering from diabetes. This is explained by the fact that this disease is characterized by an excess of the osmolarity norm, so if several tests do not show a decrease in this indicator, the specialist should prescribe the patient another treatment.

The study of serum osmolarity is carried out in order to find out the quantitative indicator of urea, glucose and sodium. Urea is the result of protein breakdown in our body. The study of osmolality allows doctors to understand the state of water-salt balance in the body of the person being studied.

Dehydration
Generally accepted medical standards for serum osmolality

The formula is very simple: Osm = 1.86 Pa G M 10.

PA is a quantitative indicator of sodium.

G – glucose concentration.

M – urea index.

As a result of the studies, it was found that in intact rats OS was 6.6 ml/100 g of weight, after administering oxytocin to the animals - 4 ml/100 g of weight. Administration of oxytocin to rats caused a decrease in OS by 39.4%, a - (Table 1, Fig. 4).

Table 1

The volume of total water in the body of rats

* — Significance of differences compared to control

Rice. 1 Total water volume

table 2

Concentration of glucose and urea in rat blood plasma

Rice. 2 Glucose and urea concentration

Table 3

Sodium concentration and osmolality of rat blood plasma

Rice. 3 Sodium concentration and osmolality

CONCLUSIONS

1. We studied the literature on the research topic.

2. The volume of total water in the body of intact rats and after the administration of oxytocin was determined.

3. The concentration of glucose and urea in the blood plasma of intact rats and after the administration of oxytocin was determined.

4. The concentration of sodium in the blood plasma and erythrocytes of intact rats and after the administration of oxytocin was determined.

5. Determination of blood plasma osmolality in intact rats and after administration of oxytocin.

LIST OF SOURCES USED

1. Ametov A.S. // Diseases of the endocrine system / A.S. Ametov // Medicine. – 2006. – No. 3 – P. 52–56.

2. Anichkov N.N. The secretion of hormones from the pituitary gland and adrenal cortex is regulated by the central nervous system in accordance with the needs of the body / N.N. Anichkov // Physiological Journal of the USSR. - 1950. - No. 36. - P. 11-12.

3. Ashmarin I.P. Neurochemistry / I.P. Ashmarin // M.: IBKh RAMS. - 1996. - 469 p.

4. Baranov V.G. Guide to clinical endocrinology / V.G. Baranov // Medicine, 1977. - 664 p.

5. Berekhin E.B. Pharmacology of the kidneys and its physiological basis / E.B Berekhin // M.: Medetsina, 1979. - P. - 23 - 48.

6. Berezov T.T. Biological chemistry/ T.T. Berezov, B.F. Korovkin // M: Medicine, 1990. - 528 p.

7. Berezov T. T. Biological chemistry / T. T. Berezov, B.F. Korovkin // - M "Medicine", 1990. - P. 56 - 83.

8. Brown F. Comparative physiology of animals / F. Brown F // trans. from English, M, 1967. P. 49 – 85.

9. Bykov K.M. Cerebral cortex and internal organs / K.M. Bykov // - M, “Medicine”, 1945. - 362 p.

10. Vaido A.I. Comparative genetic analysis of the excitability of the nervous system / A.I. Vaido, Yu.S. Dmitriev // Genetics, 1983. - No. 19 - S. - 54-103.

11. Vander A. Physiology of the kidneys / A. Vander // M.: Medetsina, 2000. - P. - 4 - 33.

Results and transcript

Transferrin: what is it, functions, definition and norms in tests, deviations.
The results obtained allow the doctor to determine the nature of the pathology and the severity of the disease. An osmolarity value ranging from 800 to 1200 mOsm/L is considered normal.

If the result shows hypoosmolarity, this may mean the following pathologies:

• Pyelonephritis.
• Kidney failure.
• Diabetes insipidus.
• Necrosis of renal tubules.
• Violation of water-salt metabolism.
• Fluid retention in the body.

The severity of violations can be determined by the degree of deviation of the indicator from the norm:

• 400-600 mOsm/l indicates a moderate decrease in the filtering function of the kidneys.
• 600-800 mOsm/l reflects primary changes in the functioning of the renal system.
• Below 400 mOsm/l indicates significant disturbances in the genitourinary area.

The hyperosmolar state (in which the value exceeds 1200 mOsm/l) is characterized by the formation of edema, hypertension, and problems with the heart.

Such a deviation from the norm is provoked by:

• Congestive heart failure.
• Renal artery stenosis.
• Dehydration.
• Glucosuria.
• Dehydration.
• Pyelonephritis.
• Shock.

A strong excess of osmolarity concentration leads to serious disturbances in the functioning of organs, coma.

Only a doctor can accurately interpret the examination. At the same time, the doctor takes into account other tests taken by the patient. Studying the clinical picture and research results provides the basis for making the correct diagnosis and selecting an effective treatment regimen.

source

If osmolality is increased, what does this mean?

Blood osmolality is considered elevated if it exceeds 295 milliosmoles per kg of blood. It can occur as a result of the following pathological conditions:

• dehydration of the body,
• diabetes insipidus,
• various head injuries,
• stroke,
• elevated glucose levels – hyperglycemia,
• increased concentration of sodium in the blood - hypernatremia,
• uremia – a condition in which the kidneys cannot cope with the removal of harmful substances from the body, resulting in intoxication,
• poisoning with ethanol, methanol or ethylene glycol.

If the blood osmolality rate decreases and falls below 275 milliosmoles per kg of blood, it is considered abnormally low. This condition may be due to several reasons:

• excessive fluid intake - overhydration,
• decreased sodium concentration in the blood – hyponatremia,
• paraneoplastic syndrome caused by a malignant tumor,
• Parhon's syndrome is a syndrome of inadequate secretion of antidiuretic hormone.

Some of these reasons are more serious, others less so. After receiving the test results, the doctor must compare them with the results of other studies, make an accurate diagnosis and prescribe appropriate treatment.

Application

Diastolic pressure - what is it, normal indicators, reasons for increased or decreased values

Diagnosis of non-ketotic hyperglycemic coma. Control of water-electrolyte balance

• Identify abnormal serum water levels to evaluate for hyponatremia
• Measurements of plasma and/or urine osmolality are more valuable in assessing hydration status than changes in hematocrit, urea, or plasma proteins, as they depend on many other factors.

Promotion

Hyperglycemia.

Diabetic ketoacidosis (osmolality should be determined constantly in decompensated diabetes mellitus).

Non-ketotic hyperglycemic coma.

Hypernatremia with dehydration

• Diarrhea, vomiting, fever, hyperventilation, inadequate water intake.
• Diabetes insipidus is central.
• Nephrogenic diabetes insipidus - congenital or acquired (hypercalcemia, hypokalemia, chronic kidney disease, sickle cell anemia, effects of certain medications).
• Osmotic diuresis - hyperlycemia, administration of mannitol.

Hypernatremia with normal hydration - occurs when the hypothalamus is damaged.

• Impaired sensitivity of osmoreceptors (primary hypernatremia) - water load does not lead to normalization of osmolarity; Chlorpropamide may lower sodium levels to near normal levels.
• Impaired thirst (hypodipsia) - drinking water quickly returns sodium levels to normal.

Hypernatremia with overhydration is iatrogenic and accidental (eg, children being fed high-sodium diets and water, or CPR with soda). Drinking alcohol; alcoholic coma with hyperosmolar status. Decreased (equivalent to hyponatremia) Hyponatremia with hypovolemia (urine sodium typically >20 mEq/L)

• Adrenal insufficiency (for example, congenital forms of adrenal hyper- and hypoplasia with sodium loss, adrenal hemorrhage, inadequate corticosteroid therapy).
• Renal losses (osmotic diuresis, proximal renal tubular acidosis, sodium-losing nephropathies, pyelonephritis, diseases of the renal medulla, polycystic kidney disease).
• Losses through the gastrointestinal tract (diarrhea, vomiting).
• Other losses (burns, peritonitis, pancreatitis).

Hyponatremia with normal volume or hypervolemia (dilution syndrome)

• Congestive heart failure, liver cirrhosis, nephrotic syndrome.
• SNS ADH.

Formulas for calculating and predicting serum osmolality (do not compete with direct osmolality measurement):

mOsmol/L = (1.86 x serum Na) + (serum glucose: 18) + (BUN: 28) + 9 (in mg/dL)

or

in SI units: = (1.86 x serum Na) + serum glucose (mmol/l) + BUN (mmol/l) + 9

easier:

Na+ + K+ 4- (BUN: 28) + (glucose: 18). But since there is relatively little potassium in the serum, and the level of urea has little effect on the distribution of water, the formula is further simplified: 2Na + + (glucose / 18).

Sources

• https://nefrol.ru/diagnostika/osmolyarnost.html
• https://medintercom.ru/articles/osmolyarnost_krovi
• https://2pochki.com/diagnostika/chto-takoe-osmolyarnost-mochi
• https://1pokrovi.ru/analizy-krovi/osmolyarnost-krovi.html
• https://med-slovar.ru/diagnostika-i-issledovaniya/analizy/12-spetsificheskie-laboratornye-issledovaniya/34-osmolyalnost
• https://www.medmoon.ru/med/osmoljalnost_krovi_norma_tablica.html

Methods for determining the indicator

Concept, composition and properties of blood

There are a number of methods based on physical laws that allow you to measure the osmolarity of urine. These methods have found implementation in the designs of osmometers designed to study the water-salt balance in human biological fluids. Among the most well-known methods for determining osmolarity are:

1. a method based on taking measurements when passing a biological fluid through a membrane made of natural or artificial materials;
2. osmometers based on the principle of reducing the vapor pressure of a substance above a liquid;
3. devices whose operating principle is based on an increase in boiling point, which occurs with an increase in the osmolarity of the mixture;
4. devices based on lowering the freezing point with increasing osmolarity of the solution are the most common design for medical research.

In addition, there are known methods for determining the indicator by the electrical conductivity of the solution and by measuring the surface tension of the liquid.

Specifics of the examination and accuracy of results

To obtain a reliable value, it is necessary to follow a number of rules, ignoring which can seriously distort the desired indicator:

• In order to prevent bacteria from entering the urine, women and men must wash their genitals and release the first few drops into the toilet before taking the test. The remaining urine is collected in prepared sterile containers.
• Individual recommendations from physicians may include advice to refrain from drinking liquids 12 hours before sample collection.
• 24 hours before the test, you must adjust your diet according to the requirements of your doctor.

The accuracy of the results may be affected by the use of medications containing sucrose and dextran. Before the test, you must inform your doctor about the medications you are taking. In addition, an unreliable result may occur if an X-ray examination using contrast liquid is performed several days before the test.

Preparing for the test

Plasma osmolarity testing is very complex because it can be influenced by many factors. To avoid repeated collection of material and not waste time, specialists insist that the patient undergo special preparation. Despite its importance, it is very simple.

First of all, the patient must tell the doctor about all the medications he is currently taking. He is obliged to listen carefully to the patient and determine whether it is possible to continue taking pharmaceuticals or whether it is better to temporarily stop so as not to affect the result of the analysis.

The second thing you need to point out to your doctor is taking dietary supplements, since they can also affect the interpretation of the study.

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Important! Blood for plasma osmolarity is donated only on an empty stomach, so the patient is prohibited from taking any food or drinks 9 hours before collecting the material.

Prohibited the day before the study:

• Smoking.
• Drink alcohol.
• There are flour products.

• Abuse sweet foods.

Experts advise eating “light” steamed food a few days before collecting whey.

If a patient regularly participates in donor programs, he can take an osmolarity test only 15-18 days after the last donor collection or blood transfusion. This pause is needed for the body to recover and correctly show its condition.

The collection of biomaterial occurs quickly and does not cause discomfort or pain to the patient. Over many years of medical practice, no complications were recorded after the test. Only in some patients did a small bruise or swelling form at the site of needle penetration. As a rule, everything went away within 2-3 days.

Indications for analysis

Urine osmolarity must be determined if the patient has the following pathologies:

• excessive urination;
• infections of the genitourinary system that cause complications;
• indirect signs indicating an increase or decrease in sodium concentration in the body;
• assessing the results of therapy for hyperosmolar comas;
• diabetes mellitus;
• diagnosis of renal dysfunction.

Normal values ​​and deviations

Normal osmolarity values ​​are considered to be fluctuations in the range of 800–1200 mOsm/L. Deviations from these values ​​manifest themselves in a decrease in osmolarity, called hypoosmolarity, or an increase in it, called hyperosmolarity. Hypoosmolarity can be caused by a violation of the water-salt balance due to overhydration, the manifestation of renal dysfunction, severe pyelonephritis and necrotization of the kidney canals. Hyperosmolarity can be associated with dehydration, stenosis of the artery in the kidney area, disruption of the heart muscle, and shock. Possible fluctuations in the indicator can be represented by the following results:

• When the value decreases to 600 mOsm/l, it indicates moderate impairment of kidney function.
• When a reading is less than 400 mOsm/L, serious kidney problems can be diagnosed.
• In the case of a change in osmolarity towards values ​​exceeding 1200 mOsm/l, it leads to the appearance of edema of varying severity, an increase in blood pressure and disturbances in the functioning of the cardiovascular system, including severe conditions and coma.

It should be noted that in some cases, to make a diagnosis, the attending physician recommends that the patient undergo a blood omolarity test. The relationship between the values ​​of the indicator for urine and blood is an important criterion for judging the presence of a disorder in the kidneys and the timely initiation of its therapy. The results obtained during the analysis allow the doctor to determine the nature of the pathology in case of violation of the concentration of electrolytes and the amount of fluid in the body

The importance of determining osmolarity is that a violation of water-mineral metabolism leads to a change in the overall metabolism of the body, which entails many different diseases

Osmolality exceeds standard value

A critical increase in serum osmolality is considered to be 298 mOsm/kg. This deviation is called hyperosmolarity. It can be provided by the following factors:

1. Severe dehydration of the body.
2. Diabetes insipidus.
3. Mechanical head bruises.
4. Strokes.
5. Increased glucose levels.
6. An increase in sodium concentration in the body.
7. The inability of the kidneys to fully remove harmful toxins from the human body, which over time leads to the development of intoxication.
8. Carbon monoxide poisoning and household chemicals.

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Types of hyperosmolarity

There are three types of hyperosmolarity conditions.

Isotonic

It is characterized by excessive accumulation of salt and water in the body, which provokes the development of heart and kidney diseases. Treatment of the deviation involves the patient taking cardiac glycosides and minimally drinking water. Pharmacological agents are prescribed:

1. Furosemide.
2. Prednisolone.
3. Triamterene.

Hypertensive

It is characterized by the accumulation of water and salts in blood vessels and intercellular membranes, causing low hemoglobin, protein and hematocrit. Therapeutic measures include:

1. A solution of insulin and glucose.
2. Albumen.
3. Lasix.
4. Veroshpiron.

Important! Depending on the patient’s condition, hemodialysis and peritoneal therapy are performed. It is strictly forbidden to administer crystalloids.

Hypotonic

Accumulation of fluid in blood vessels, in the cell and its membranes. Because of this, sodium, protein and hemoglobin drop sharply in the body. Therapy involves the use of mannitol solution, hypertonic mixtures and corticosteroids. To accelerate fluid removal, hemodialysis with ultrafiltration mode is performed.

Osmolality (blood)

Key words: renal failure diabetes insipidus blood

Osmole - When determining the concentration of a solution in terms of the number of particles, instead of grams, a unit called the osmole is used.

One osmole is 1 gram molecule of an osmotically active solute. So, 180 g of glucose, i.e. 1 gram molecule of glucose is equivalent to 1 osmole of glucose, since glucose does not dissociate into ions. If a solute dissociates into 2 ions, 1 gram molecule of solute will correspond to 2 osmoles, since the number of osmotically active particles in this case is twice as large as for a non-dissociating solute. When completely dissociated, 1 gram molecule of sodium chloride, or 58.5 g, is equivalent to 2 osmoles (i.e., the osmolarity of a 1-molar NaCl solution will be 2 osmol/l).

A solution containing 1 osmol of solute in every kilogram of water is said to have an osmolality of 1 osmol per 1 kg. A solution containing 1/1000 osmol of solute per kg has an osmolality of 1 milliosmol (mosm) per kg. The normal osmolality of extracellular and intracellular fluids is approximately 300 mOsm per 1 kg of water.

Serum osmolality is a quantitative measure of osmotically active substances dissolved in blood serum, i.e. the sum of the concentrations of cations, anions and non-electrolytes, expressed in milliosmoles per kilogram of water (mOsm/kg H 2 O). The main anions that determine serum osmolality include sodium and other anions (potassium, chlorine, bicarbonate ions, etc.). A more accurate measurement also takes into account the glucose and urea content, finding an expression in the formula:

Serum osmolality= 2Na + + serum glucose + urea (urea nitrogen)

Plasma osmolality can be determined by knowing the concentration of the main osmotic components of the extracellular fluid - sodium, glucose and urea. For example: sodium is 140 mEq/L, glucose is 4 mmol/L, blood urea is 6 mmol/L. Plasma osmolality = 2 x Na + glucose (mmol/l) + urea (mmol/l) = 2 x (140) + 4 + 6 = 290 mOsm/kg H2O

One of the main factors regulating antidiuretic hormone (ADH) secretion and thirst is plasma osmolality. Osmoreceptors located in the hypothalamus are sensitive to fluctuations in osmolality. A change of 1% already leads to noticeable changes in ADH secretion.

When determining blood osmolality, two main conditions are distinguished: hyperosmolality and hypoosmolality.

Hyperosmolality is caused by an increase in serum osmolality, which is one of the common causes of coma in diabetes mellitus and brain dehydration. As blood osmolality increases, ADH secretion increases. When the osmolality reaches about 295 mOsm/kg, the concentration of ADH becomes sufficient to ensure the maximum antidiuretic effect (urine volume less than 2 l/day; urine osmolality more than 800 mOsm/kg). At the same time, the thirst quenching mechanism is activated, which leads to an increase in water consumption and prevents dehydration of the body.

Hypoosmolality is a decrease in blood osmolality. Hypoosmolality can lead to osmotic cerebral edema and the development of intracranial hypertension syndrome. The reason for the decrease in osmolality can be various factors, for example, an excess of free water contained in the blood plasma relative to the volume of kinetic particles dissolved in it. When blood osmolality decreases below the threshold level (about 280 mOsm/kg), ADH secretion is inhibited. This leads to the excretion of a large volume of maximally diluted urine. Increased water excretion prevents a further decrease in plasma osmolality, even with significant water intake.

The osmolal concentration of urine ranges from 50 to 1400 mosmol/l (in plasma 295 mosmol/l). When the osmolal concentration of urine is higher than that of plasma, the difference between these values ​​indicates the amount of solutes removed from the plasma without equivalent loss of water. For example, if with a daily urine volume of 2 liters the osmolality is 100 mOsmol/L, then the clearance will be 1.43 liters of free water during this period. The lowest osmolality is observed in uncontrolled diabetes insipidus.

Help of osmometry and osmolarity calculation in diagnosis and treatment

Determining the osmolarity of blood and urine, calculating the osmolarity index and free water clearance using the formula are by no means simple studies. Various methods of osmometry (method of increasing the boiling point, method of depression of the freezing point) are not used by every medical institution and are complex laboratory tests.

However, in medicine, blood osmolarity is considered an important diagnostic criterion, since this indicator allows one to establish a number of pathological conditions or even predict them (the development of acute renal failure) when classical indicators do not yet respond. Obviously, this primarily concerns severe kidney diseases.

The concentrations of creatinine and urea studied in such situations will change only after some time (AKI - from 3 to 4 days), when half of the structural units of the kidney involved in the production of urine (nephrons) fail and will not be able to fulfill their functional purpose. Determination of plasma and urine osmolarity, osmolarity index and free water clearance will make it possible to predict and/or detect the development of acute renal failure already on days 1–2.

Thus, this indicator will be applied and will assist in diagnosis:

• Acute renal failure at the earliest stage of formation;
• Hypoosmotic syndromes (a drop in the level of the indicator below 280 mOsm/l), accompanied by a number of nonspecific symptoms: headache, fatigue, lethargy, nausea, causeless vomiting;
• Hyperosmotic syndromes (an increase in the numerical values ​​of osmolarity - above 350 mOsm/l), which most often create conditions for the development of comatose states in diabetes mellitus (diabetes mellitus);

• Causes of hyponatremia (decreased concentration of sodium cations – ↓Na);
• Hypernatremia (increased content of sodium cations – Na);
• Pseudohyponatremia, caused by an increase in the concentration of fats (hypertriglyceridemia) and proteins (hyperproteinemia), the molecules of which are larger in size than sodium molecules and do not affect changes in blood osmolarity;
• TUR syndrome (water intoxication syndrome, as a complication of certain operations, for example, resection of the prostate gland);
• Diabetes insipidus (diabetes insipidus), diabetes mellitus (hyperglycemic conditions, diabetic ketoacidosis);
• Poisoning with toxic substances that also belong to the group of osmotically active substances (ethanol, methanol, ketone bodies, lactate, ethylene glycol, etc.);
• Acute increase in intracranial pressure (intracranial hypertension - ICH).

In addition, this laboratory test will help in the treatment of diseases requiring transfusion and infusion measures (assessment of the effectiveness of therapy), as well as hypoosmolar overhydration and coma, accompanied by an increase in blood plasma osmolarity.

Specifics of the study

Several basic values ​​are assessed, which are studied by specialists in the resulting material. After the examination and grouping of the necessary data is completed, laboratory assistants enter the obtained indicators into a special correspondence table, with the help of which acceptable values ​​​​and their violations are later displayed.

Checking the osmotic concentration is determined by the following factors:

• To obtain information about the amount of fluid in the blood.
• As a source of indicators of the chemical composition of serum.
• To monitor increases and decreases in serum fluid concentrations.
• To check the level of the hormone that is responsible for fluid retention in the body;
• To detect the underlying causes of dehydration and swelling of the extremities.
• To diagnose the body for the presence of pathological processes.
• To diagnose the presence of poisons, methanol and other dangerous substances.

The study of plasma osmolarity is characterized by the content of chemical substances in it. To carry out the event, the laboratory assistant takes venous blood from the patient.

Several basic values ​​are assessed, which are studied by specialists in the resulting material. After the examination and grouping of the necessary data is completed, laboratory assistants enter the obtained indicators into a special correspondence table, with the help of which acceptable values ​​​​and their violations are later displayed.

What does the analysis show?

How to understand the tests you receive? This is probably possible if you try to follow the guidelines below:

1. It is known that changes in blood plasma osmolarity parallel fluctuations in the content of sodium cations in it. Consequently, an increase in Na concentration (hypernatremia) and an increase in TSC (more than 290 mOsm/l) will lead to an increase in the activity of the drinking center, the person will not leave the feeling of thirst, and stimulation of vasopressin synthesis will begin to prevent the removal of water resources from the body. An increase in blood plasma osmolarity by 50–60 mOsm/L is a dangerous sign, since in this situation the patient may die from cerebral edema.
2. And, conversely, a decrease in Na levels (hyponatremia) and a decrease in TSC (below 280 mOsm/l), inhibiting the production of vasopressin, promotes increased release of water from the body through the kidneys.

Meanwhile, everything is not so simple, since, focusing on sodium concentration, you can encounter paradoxical situations that should be taken into account, for example: sodium in the blood and TSC decrease, and urine osmolarity increases. At the same time, an increase in Na content is noted in overly concentrated urine. Such circumstances may be due to the influence of such an etiological factor as SIADH (syndrome of inappropriate secretion of antidiuretic hormone), in which the production of ADH does not depend on how much the body needs water.

And it turns out that to complete the picture indicating the state of the body, it is necessary to determine the amount of sodium in the blood and urine, as well as carry out an analysis of the osmolarity of these biological media. In addition, the analysis form must contain such indicators as blood sugar (hyperglycemia increases TBC) and urea.

Of course, there are other examples of discrepancies between some indicators, but this information can only confuse the patient. And we are talking only about blood osmolarity...

Features of osmolarity

An increased blood osmolarity provokes a decreased urine osmolarity. This imbalance is the main symptom of abnormalities in the renal parenchyma. The slightest violation of this norm is provoked by the processes that are responsible for the distribution of fluid in the body.

According to basic physiology, a person needs to consume 1-2 liters of water daily for normal existence, since it enriches the body with useful substances and microelements. Most of them enter us through drinking, the rest through liquid found in food. Unnecessary or waste water is removed from the body by the epidermis, pulmonary, intestinal and renal systems. The daily rate of fluid excreted in urine and feces is 0.8 - 1 liter.

If a person’s water balance is disturbed, or fluid is not properly removed from the body, the osmolarity of blood and urine is disrupted. An excess of fluid provokes swelling and heaviness in the limbs, and a lack of it will cause severe dehydration and plasma viscosity.

More than 30 percent of serious diseases develop due to impaired water balance. For example, excess fluid and electrolyte imbalance in most cases cause:

• Kidney diseases.
• Cardiac pathologies.
• Blood diseases.
• Circulatory disorders.

Fluid deficiency provokes the following changes in the body:

• Excess glucose in the blood.
• Diseases of the adrenal glands and kidneys.
• Diabetes.

Thanks to osmolarity analysis, it is easier for a specialist to determine the state of water-salt balance and, if necessary, correct it with medications.

Determination of the osmotic window

1.86× N M G 9, where

N – sodium concentration in plasma;

M – urea level;

G – glucose content.

All these microelements are calculated additionally.

Next, the results obtained are substituted into the basic formula: Actual Osm - Theoretical Osm. The end result is the osmotic window.

1.86× N M G 9, where

Checking this indicator will not be easy even for an experienced laboratory technician. Such a study makes it possible to identify the initial stages of many deviations and pathologies. As a rule, the value of blood plasma osmolality is characterized by an increase or decrease in general norms. Various factors can provoke deviations.

Important! Blood plasma osmolarity is normal only if there are no even minimal violations of generally accepted values.

Blood plasma osmolarity

In medicine, there are two types of blood osmolarity disorders - hyperosmolarity and hypoosmolarity. Hyperosmolarity refers to a high concentration of active particles, and hypoosmolarity refers to a too low level of active particles.

If blood biochemistry shows a low osmolarity concentration, then the patient expresses this:

1. Severe weakness.
2. Unreasonably rapid fatigue.
3. Systematic attacks of nausea.
4. Vomiting.
5. Drowsiness.

Gagging The
following manifestations are typical for hyperosmolarity:

1. Numerous pathological reflexes.
2. Decreased concentration.
3. Depression and apathy towards what is happening.
4. Rare urination.
5. Disruption of the facial nerves.
6. Impaired swallowing and chewing reflexes.
7. Low body temperature.
8. Unreasonably damp skin.

Wet skin
To put it simply, osmolarity is the concept of how thick or thin the blood is. Any deviations from the norm are harbingers of serious diseases or pathological changes in the body.

To carry out the analysis, a specialist requires blood plasma. Such studies in most cases provide insight into the health status of a person suffering from diabetes. This is due to the fact that diabetes provokes “thickening” of the blood, which, in turn, affects increased osmolarity levels.

This study also helps to select the most appropriate therapy for numerous diseases, monitor its results, and prevent the development of complications and side effects.

Determination of osmolality of aqueous solutions

The following methods can be used to determine osmolality: cryoscopic, membrane and steam osmometry.

Cryoscopic method

The method is based on lowering the freezing point of solutions compared to the freezing point of a pure solvent.

1 osmol per kilogram of water lowers the freezing point by 1.86 °C. Measuring these changes is the basis of the cryoscopic method.

This dependence can be expressed by the following formula:

Where:

Sosm - osmolality of the solution (mOsm/kg)

T2 is the freezing temperature of a pure solvent (˚C);

T1 is the freezing temperature of the test solution (˚C);

K is the cryometric constant of the solvent (for water: 1.86).

Currently, the determination of the osmolality of solutions is carried out using automatic cryoscopic osmometers.

The required amount of the test solution is placed in the cell of the device. Next, the measurement is carried out according to the instructions included with the device. If necessary, the device is calibrated using standard solutions of sodium or potassium chloride that cover the detectable osmolality range (Table 1).

Table 1 - Standard reference values ​​for the freezing point depression and the efficiency of the osmotic concentration of aqueous solutions of sodium and potassium chlorides

Membrane osmometry method

The method is based on the use of the property of semi-permeable membranes to selectively allow molecules of substances to pass through.

The driving force behind the process is the process of osmosis. The solvent penetrates the test solution until equilibrium is established; the additional hydrostatic pressure that arises is approximately equal to the osmotic pressure and can be calculated using the formula:

(5)

Where:

Osmolality can be calculated using the formula:

Сcm =pcmR ∙ T (6)

where R is the universal gas constant (8.314 J/molK)

T – absolute temperature (˚K).

Note. This method is applicable only for solutions of high molecular weight substances (104 – 106 g/mol). When analyzing solutions containing electrolytes and other low molecular weight substances, only the osmotic pressure created by high molecular weight components of the solution will be determined.

Determination of the osmolality of the test solution is carried out using a membrane osmometer. Preliminary calibration of the device and measurements are carried out in accordance with the instructions for the device.

Steam osmometry method

1 osmol per kilogram of water lowers the vapor pressure by 0.3 mmHg. Art. at a temperature of 25 °C. Measuring these changes is the basis of vapor osmometry.

The method is based on measuring the temperature difference that occurs across thermistors placed in a measuring cell saturated with solvent vapor if a drop of pure solvent is applied to one of them and a drop of the test solution is applied to the other. The temperature difference occurs due to the condensation of solvent vapor on a drop of solution, since the vapor pressure of the solvent above this surface is less. In this case, the temperature of the solution drop increases due to the exothermic condensation process until the vapor pressure above the solution drop and the pressure of the pure solvent in the cell are equal. When pure solvent is applied to both thermistors, the temperature difference is zero. The temperature difference is practically proportional to the molal concentration of the solution.

The osmolality of the test solution is determined using a steam osmometer. Preliminary calibration of the device and measurements are carried out in accordance with the instructions for the device.

Download in PDF GPM.1.2.1.0003.15 Osmolarity

SALT.

Norm: none.

Pathology options:

Interpretation of results: hypovolemia (diarrhea, vomiting, excessive sweating), severe pneumonia, leukemia when taking cystostatic drugs.

Interpretation of results: hypovolemia (diarrhea, vomiting, excessive sweating), severe pneumonia, leukemia when taking cystostatic drugs.

Interpretation of results: inflammation of the urinary tract (pyelonephritis, cystitis, etc.).

Interpretation of results: rheumatism, anemia.

Interpretation of results: has no diagnostic value, may occur when using sulfur mineral waters.

Interpretation of the results: diabetes mellitus, consumption of lingonberries, blueberries, intake of salicylic and benzoic acids.

Interpretation of results: intake of plant foods, cystitis.

Interpretation of the results: repeated vomiting, frequent gastric lavage.

Interpretation of results: no diagnostic value.

Interpretation of the results: eating large amounts of tomatoes, spinach, sorrel, apples, grapes, oranges.

Interpretation of results: no diagnostic value.

Interpretation of results: hereditary cystinosis.

Interpretation of results: protein decomposition products, liver diseases, B-12 deficiency anemia, leukemia.

Interpretation of the results: products of the cleavage of purine bases, promotes stone formation.

Typical results: amyloidosis, renal tuberculosis, cystitis.

Interpretation of results: hyperbilirubinemia.

Interpretation of results: bleeding from the urinary tract.

Interpretation of results: intravascular hemolysis.

Interpretation of results: fatty degeneration of organs.

Interpretation of results: treatment with sulfonamide drugs.

What does it consist of??

The process by which urine is concentrated or diluted is a very complex one, requiring the proper integration of two independent renal systems: the creation of a solute gradient and antidiuretic hormone activity.

Urine concentration and dilution

The creation of an osmolar gradient of solutes occurs in the loop of Henle and in the renal medulla. There, urine osmolarity increases from values ​​similar to those of plasma (300 mOsm/kg) to levels close to 1200 mOsm/kg, all due to the reabsorption of sodium and chloride in the thick portion of the ascending loop of Henle.

Urine then passes through the cortical and medullary collecting tubules, where water and urea are reabsorbed, helping to create osmotic gradients.

Likewise, the thin portion of the ascending loop of Henle helps reduce urine osmolarity due to its permeability to chlorine, sodium and, to a lesser extent, urea.

As the name suggests, antidiuretic hormone prevents or reduces the release of urine to normally conserve water.

This hormone, also known as vasopressin, is then activated in situations of high plasma osmolarity (>300 mOsm/kg) to absorb water, which ultimately dilutes the plasma but concentrates the urine.

Other indicators related to USC

Thus, osmolarity of blood (plasma or serum) is an important parameter indicating the preservation or disorder of the dynamic balance of water in the body. It is measured using special laboratory equipment or calculated using a formula after carrying out the necessary biochemical tests (sodium, urea, glucose).

In addition to the described object of study (osmolarity), the table above shows other laboratory tests: free water clearance (SWR - a rather sensitive and important indicator of the concentrating ability of the kidneys) and osmolarity index (IO - the ratio of urine osmolarity to blood plasma). They are directly related to determining the functional abilities of the kidneys during the development of acute renal failure (ARF) and are also calculated using formulas.

True, and that’s not all: there is another indicator related to osmolarity, which is called the osmotic window. Its norm is less than 6 mOsm/l. The osmotic window is measured in mOsm/l or mOsm/kg, calculated based on the values ​​of the osmotic window obtained by osmometry - actual, and the osmotic value derived from the formula - theoretical:

Osmotic window = OSK fact. – USC theory.

For example, 287 mOsm/kg – 284 mOsm/kg = 3 mOsm/kg (corresponds to the norm). If the osmotic window is more than 6 but less than 10 mOsm/L, then doctors suspect the development of keto-, lactate- or renal acidosis. If the level of this indicator crosses 10 mOsm/l and tends to increase, then there is reason to think about severe poisoning (ethyl or methyl alcohol, as well as other organic substances that can affect OSC).