Clinical and diagnostic value of urea determination. Details about the determination of urea in blood serum Determination of urea concentration

Urea is the main breakdown product of proteins. It is the chemical form in which nitrogen that the body does not need is removed through urine.

The accumulation of urea and other nitrogen-containing compounds in the blood due to renal failure leads to uremia.

Synonyms Russian

Carbonic acid diamide, urea, urea in the blood.

SynonymsEnglish

Urea nitrogen, Urea, Blood Urea Nitrogen (BUN), Urea, Plasma Urea.

Research method

UV kinetic test.

Units

mmol/l (millimoles per liter).

What biomaterial can be used for research?

Venous, capillary blood.

How to properly prepare for research?

• Do not eat for 12 hours before the test.
• Avoid physical and emotional stress and do not smoke 30 minutes before donating blood.

General information about the study

Urea is one of the end products of protein metabolism, containing nitrogen. It is produced in the liver, transported by the blood to the kidneys, where it is filtered through the glomerulus and then excreted. The urea test result is an indicator of glomerular production and urine excretion.

Metabolized nitrogen is found in the body in the form of ammonia, produced from the remains of protein breakdown and processing. Ammonia in the liver combines with carbon dioxide to form urea. Rapid protein breakdown and kidney damage rapidly raise blood urea levels (as does virtually any massive cell death).

The amount of urea secreted is directly dependent on the level of protein consumed by a person; it increases during feverish conditions, with complications of diabetes and with increased hormonal function of the adrenal glands. Elevated urea levels are a marker of decreased glomerular filtration.

Urea is one of the main metabolites in the blood; the body does not use it in any way, but only gets rid of it. Since this excretion process is continuous, a certain amount of urea is always in the blood.

The level of urea should be interpreted inseparably from creatinine values. The term "uremia" is used when the concentration of urea in the blood rises above 20 mmol/l.

Azotemia, also indicated by an increase in urea concentration, is most often a consequence of inadequate excretion due to kidney disease.

Blood urea levels decrease in many liver diseases. This occurs due to the inability of damaged liver cells to synthesize urea, which in turn leads to increased ammonia concentrations in the blood and the development of hepatic encephalopathy.

Renal failure occurs when the glomerulus loses its ability to filter blood metabolites through itself. This can occur suddenly (acute renal failure) in response to illness, administration of drugs, poisons, or injury. Sometimes this is a consequence of chronic kidney diseases (pyelonephritis, glomerulonephritis, amyloidosis, kidney tumors, etc.) and other organs (diabetes, hypertension, etc.).

A urea test is usually ordered in combination with a creatinine test.

What is the research used for?

• To assess kidney function in a range of conditions (in conjunction with a creatinine test).
• For the diagnosis of kidney disease and for checking the condition of patients with chronic or acute renal failure.

When is the study scheduled?

• Urea is tested during a biochemical study:
  • for nonspecific complaints,
  • when assessing renal function before prescribing drug therapy,
  • before hospitalization of a patient due to an acute illness,
  • when a person is in a hospital.
• For symptoms of kidney dysfunction:
  • weakness, fatigue, decreased attention, poor appetite, sleep problems,
  • swelling of the face, wrists, ankles, ascites,
  • foamy, red or coffee-colored urine
  • decreased diuresis,
  • problems with urination (burning, intermittency, predominance of nocturnal diuresis,
  • pain in the lumbar region (especially on the sides of the spine), under the ribs,
  • high pressure.
• In addition, this analysis can be carried out periodically:
  • to check the condition of patients with chronic kidney disease or non-renal chronic diseases such as diabetes, congestive heart failure, myocardial infarction, arterial hypertension, etc.,
  • before and during drug therapy to determine the state of kidney function,
  • after dialysis sessions to assess their effectiveness.

What do the results mean?

Reference values

Reasons for increased urea levels:

• decreased renal function caused by congestive heart failure, loss of salts and fluids, shock in combination with excessive protein catabolism (gastrointestinal bleeding, acute myocardial infarction, stress, burns),
• chronic kidney disease (pyelonephritis, glomerulonephritis, amyloidosis, renal tuberculosis, etc.),
• obstruction of the urinary tract (bladder tumor, prostate adenoma, urolithiasis, etc.),
• bleeding from the upper gastrointestinal tract (peptic ulcer of the stomach, duodenum, cancer of the stomach, duodenum, etc.),
• diabetes mellitus with ketoacidosis,
• increased protein catabolism in cancer,
• taking corticosteroids, nephrotoxic drugs, tetracyclines, excess thyroxine,
• use of anabolic steroids,
• food high in protein (meat, fish, eggs, cheese, cottage cheese).

Reasons for low urea levels:

• liver failure, some liver diseases: hepatitis, cirrhosis, acute hepatodystrophy, liver tumors, hepatic coma, poisoning with hepatotoxic poisons, drug overdose (this disrupts urea synthesis),
• acromegaly (a hormonal disease characterized by increased production of somatotropic hormone),
• fasting, low protein diet,
• impaired intestinal absorption (malabsorption), for example, with celiac disease,
• nephrotic syndrome (increased protein excretion in the urine, hyperlipidemia, decreased protein levels in the blood),
• increased production of antidiuretic hormone (ADH) and, as a consequence, pathological hypervolemia,
• pregnancy (increased protein synthesis and increased renal filtration cause a decrease in the amount of urea in pregnant women).

What can influence the result?

The concentration of urea in the blood can only be determined through laboratory biochemical analysis.

A high level of this compound is highly likely to indicate reduced functional activity of the kidneys. With high numbers, it cannot be ruled out that there is a progressive renal failure.

An increase in urea levels may indicate the following disorders:

note

The concentration of urea in the blood can increase due to heavy physical exertion, which causes accelerated breakdown of proteins. In such cases, there is a transient and not very significant increase in the indicator relative to the physiological norm.

In case of kidney pathologies accompanied by a violation of their excretory function, the patient’s hemoglobin level drops, blood pressure increases , weakness, general malaise and pallor of the skin appear. The cause of renal dysfunction leading to an increase in urea levels may be pathologies of the endocrine glands, in particular, dysfunction of the pancreas ( diabetes with ketoacidosis) or hyperfunction of the thyroid gland, which negatively affects protein metabolism.

Indicators for increased protein catabolism or blood flow disorders do not exceed 13 mmol/l. In chronic renal failure, the urea concentration can reach 40-50 mmol/l, and in acute renal failure it is ≥ 81 mmol/l.

An increase in this indicator is not considered an early symptom of renal dysfunction. First, the concentration of uric acid increases, and only then - urea and creatinine.

Assessment of the degree of kidney damage by urea concentration:

1. within 16 mmol/l – moderate severity;
2. 16.1-33.2 mmol/l – severe;
3. more than 49.8 mmol/l – very severe course of the process (unfavorable prognosis)

Against the background of large fluid loss due to gastrointestinal disorders, the level of passive reabsorption (reverse absorption) of urea in the kidney tubules increases.

If the urinary tract is obstructed due to compression or blockage, the process of urine flow is disrupted. In some cases, blood appears in the urine (gross hematuria).

With pathologies of the cardiovascular system, the passage of blood through the kidneys is disrupted, so it is not sufficiently purified.

One of the reasons for the increase in urea concentration in the blood may be an excessively high intake of protein compounds from food. The level of urea formation is directly proportional to the amount of proteins broken down in the digestive system. Urea concentration tends to increase with a diet low in chlorine ions. In this case, there is a compensatory-adaptive reaction of the body, the purpose of which is to maintain normal colloid-osmotic blood pressure.

A serious disease such as leukemia leads to an accelerated breakdown of protein compounds, i.e., an increase in their catabolism, which also causes an increase in urea levels.

>The amount of urea in the blood increases when oxalic acid, phenol or mercury compounds enter the body.

An increase in carbamide levels in the blood can result from taking the following pharmacological drugs:

• Furosemide (Lasix):
• A number of penicillin and cephalosporin antibiotics;
• sulfonamides;
• NSAIDs;
• Preparations of fluorine, lithium and heavy metals;
• Acyclovir;
• Antihypertensive and vasoconstrictor drugs.

The level of urea also increases during therapy with glucocorticosteroids, anabolic steroids, sulfonamides and thyroxine (a large amount of thyroid hormone).

Urea

is a chemical compound that appears in the body as a result of the breakdown of proteins. These transformations occur in several stages, and urea is the final product. Normally it is formed in

liver

From there it goes into the blood and is excreted

kidneys

during the filtration process.

Urea itself has no serious significance for the body. It does not perform any functions in the blood or internal organs. This compound is necessary for the safe removal of nitrogen from the body.
Normally, the highest concentration of urea is observed in the blood and urine. Here it is determined by laboratory methods for medical reasons or during a preventive examination.

From a diagnostic point of view, urea is an important indicator that can indicate a number of abnormalities in the body. The level of urea indirectly indicates the functioning of the kidneys and liver. In combination with others blood tests And urine tests this provides extremely valuable diagnostic information. Many treatment protocols and generally accepted standards are based on the results of urea testing.

How does the biosynthesis (formation) and hydrolysis (decomposition) of urea occur in the body?

The formation of urea occurs in the body in several stages. Most of them (

including the synthesis of urea itself

) occurs in the liver. The breakdown of urea normally does not occur in the body or occurs in small quantities and has no diagnostic value.

The process of formation of urea from proteins goes through the following stages:

• Proteins break down into simpler substances - amino acids containing nitrogen.
• The breakdown of amino acids leads to the formation of toxic nitrogen compounds that must be eliminated from the body. The main volume of these substances is excreted in the urine. Most of the nitrogen goes to the formation of urea, slightly less - to the formation creatinine , and a small part - on the formation of salts, which are also excreted in the urine.
• In the liver, urea is formed as a result of biochemical transformations ( ornithine cycle). From here it enters the blood and circulates in the body for some time.
• As blood passes through the kidneys, harmful substances are retained and concentrated through the filtration process. The result of this filtration is secondary urine, which is eliminated from the body during urination.

In a number of pathologies, disturbances at various levels may occur in this chain. Because of this, the concentration of urea in the blood or urine may change. Abnormalities in the results of other tests also often appear. Based on these results, a qualified specialist can make a diagnosis or draw conclusions about the condition of the body.

How is urea different from uric acid?

Urea and

uric acid

- two different substances found in the human body. Urea is a breakdown product of proteins, amino acids and a number of other compounds. Normally it circulates in the blood (

small part

) and is excreted in the urine. Uric acid is formed as a result of the breakdown of purine bases. This process occurs mainly in the brain, liver and blood. It is aimed at neutralizing ammonia (

toxic nitrogen compound

). Uric acid can be excreted from the body in small amounts through sweat and urine.

If the accumulation of urea in the body does not in itself pose a serious danger ( it only indicates various diseases), then uric acid can accumulate in various tissues in the form of salts. The most serious pathology associated with uric acid metabolism disorders is gout. .

What does the level of urea in blood and urine show?

Normally, the concentration of urea in the blood and urine is affected by the work of the liver and kidneys. Thus, deviations of its concentration from the norm can be analyzed to diagnose various pathologies of these organs. To obtain more complete information, the results of biochemical tests for other substances are also taken into account.

In general terms, urea level deviations can be interpreted as follows:

• Decreased urea levels in the blood. This deviation may occur when fasting And diet , poor in proteins. If there are no obvious reasons, various liver pathologies should be suspected. That is, in the body, the breakdown of proteins occurs in the usual manner, but for some reason the liver does not neutralize ammonia, transforming it into urea.
• Increased urea levels in the blood. A slight increase in combination with an increased level of urea in the urine can be considered normal. An accelerated breakdown of proteins occurs in the body and, as a result, more urea is formed. If the concentration is increased several times, this usually indicates serious kidney disease. The blood is poorly filtered, and a significant part of the urea is retained in the body.
• Decreased urea levels in urine. Normally, the kidneys excrete a relatively stable amount of urea per day from the body. If the level of urea in the blood is increased and the level in the urine is low, this indicates that the kidneys are not performing their functions well. The blood is less well filtered, and toxic substances can be retained in the body. This deviation most often occurs in various kidney diseases, but it can also indicate a number of metabolic disorders or some systemic pathologies ( for example, many autoimmune diseases can damage the filtration apparatus of the kidneys).
• Increased level of urea in urine. This deviation is almost always associated with an increased level of urea in the blood. Increased breakdown of proteins ( for various reasons) leads to accelerated formation of urea. Healthy kidneys usually cope with this problem and begin to excrete this substance in the urine more quickly.

renal failure

there is a direct proportional relationship between the concentration of urea in the blood and the degree of kidney damage. The slower blood filtration occurs, the more urea is retained in the body. In intensive care units, urea levels (

in conjunction with the results of other analyzes

) are used as indications for

hemodialysis

and in general for choosing treatment tactics. Thus, urea tests are most important for patients with kidney failure.

What organs influence the formation of urea ( liver, kidneys, etc.)?

Urea, like many other chemicals in the human body, is formed in the liver. It is this organ that combines many functions, including the neutralization of certain metabolic products. During normal liver function, toxic nitrogenous compounds are converted into urea and released into the blood.

The second organ that affects urea levels is the kidneys. This is a kind of filtration apparatus of the body that cleanses the blood of unnecessary and harmful substances. During normal kidney function, most of the urea is excreted from the body in the urine.

Other organs can indirectly influence the rate of formation and excretion of urea from the body. For example, thyroid by producing too much hormones (hyperthyroidism), stimulates the breakdown of proteins, which is why the liver has to quickly convert their breakdown products into urea. However, it is the liver and kidneys that directly influence the level of this substance in the blood.

What is the role and function of urea in the human body?

Urea does not perform any functions in the human body. It is an excipient, a breakdown product of proteins and amino acids, which can be easily excreted from the body. This is a kind of transport form for substances that are no longer needed. In addition, the formation of urea by the liver saves the body from the accumulation of toxic substances (

ammonia, etc.

). Thus, the main role of urea in the body is the removal of nitrogen metabolic products.

How are urea and other metabolic products removed from the body?

Urea is the main product of nitrogen metabolism (

proteins, amino acids, etc.

). Normally, it is eliminated from the body in several stages. Urea synthesized in the liver circulates in the blood for some time and then enters the kidneys. Here it passes through the filtration membrane and is retained in the primary urine. A number of substances useful to the body and most of the water are then absorbed back through the process of reabsorption (

in the renal tubules

). A small portion of urea may also return to the bloodstream. However, most of it enters the renal pelvis as part of secondary urine.

Causes of high and low urea levels

The concentration of urea in the blood can increase or decrease in several ways. In this case, various mechanisms are involved, for which different organs and systems are responsible. A urea test involves assessing the functioning of these organs. Sometimes it can be difficult to recognize the cause and mechanism of increased urea levels. To do this, doctors usually prescribe additional diagnostic tests. The following mechanisms and factors can influence the increase in urea levels in the blood:

• Blood protein concentration ( increased urea formation). The level of proteins in the blood partly affects the rate of their breakdown. The more protein breaks down, the more urea is formed in the liver, and the more it enters the blood. For example, after operations, injuries or burns a large number of cells die, and many breakdown products enter the blood ( including proteins).
• Diet. A significant amount of proteins enters the body with food. The richer the diet in proteins, the more proteins there will be in the blood. However, this mechanism does not have as much effect on the concentration of urea in the blood or urine.
• Circulating blood volume. As a result of physiological or pathological processes, the volume of blood in the human body may change. For example, massive bleeding , diarrhea or prolonged fever reduce blood volume, and numerous droppers, increased fluid intake or certain diseases increase it. A change in the volume of circulating blood affects the concentration of urea in the blood or urine due to its dilution, but its quantity (as a substance) does not change.
• Liver condition. Urea is formed in the liver from protein breakdown products ( nitrogen compounds) during normal operation of this organ. Various liver diseases lead to the fact that its cells perform their functions worse. Because of this, the formation of urea may decrease, and other toxic substances will accumulate in the blood.
• Kidney condition ( removal of urea from the body). Urea, which is formed in the liver, circulates in the blood for some time, after which it is excreted by the kidneys in the urine. In some kidney diseases, the filtration process may be slower, and the level of urea in the blood will increase, even if it is formed at a normal rate and in normal quantities.
• Other factors. Many different factors are responsible for protein metabolism, the formation of urea and its removal from the body. enzymes , cells and their receptors. There are many different diseases ( usually rare), which affect certain links in the protein metabolic chain. Some of these diseases are genetic and difficult to treat.

Why does a child’s urea increase?

An increase in urea levels in a child may be associated with various pathologies. Serious kidney disease in children is relatively rare. The most common cause is various infectious diseases of childhood and adulthood (

intestinal, respiratory, etc.

). In most cases they are accompanied

temperature rise

Which affects the concentration of urea in the blood.

In addition to infectious diseases, the following causes of increased urea levels in the blood are possible:

newborns

In children, serious deviations from the norm can be observed in the case of congenital deficiency of certain enzymes responsible for the metabolism of proteins in the body. Such diseases are associated with genetic disorders and are relatively rare.

It is usually not possible to independently determine the cause of increased urea in children. The results of the analysis must be interpreted pediatrician , who will assess the general condition of the child and take into account the results of other laboratory tests.

Low urea in children usually occurs when hepatitis (inflammation of liver tissue) of various origins.

Why does urea increase or decrease during pregnancy?

Normal during

pregnancy

An increase in urea levels during pregnancy most often indicates the development of some pathological processes. For example, when nephropathy During pregnancy, renal filtration worsens, and urea begins to accumulate in the blood ( at the same time it will be reduced in urine). In addition, pregnancy can provoke an exacerbation of various chronic pathologies, metabolic disorders or hormonal imbalances , which often affect kidney function. If during pregnancy a biochemical analysis reveals an increased concentration of urea in the blood, consultation with a specialist and additional examinations are required.

Does the consumption of water and other liquids affect the concentration of urea?

Excessive or insufficient fluid intake has a definite effect on the results of almost all laboratory tests. The fact is that increased drinking of water, one way or another, leads to an increase in the volume of circulating blood. Thus, the concentration of substances will be reduced. For the analysis, a standard volume of blood is taken, but a significant part of it will be water. Consuming large amounts of fluid will lead to a slight decrease in urea concentration, and dehydration will lead to an increase. These deviations will not affect your health, since the amount of urea in both cases is the same. It disintegrates and is excreted normally. Only the volume of blood in which it is dissolved changes.

Does diet affect urea levels in plasma, serum, blood and urine?

Diet and foods consumed can partly affect the concentration of urea in the blood and urine. A diet high in protein causes that protein to begin to break down. Urea is a product of this breakdown, and more of it is formed.

Vegetarian diet

with reduced protein intake reduces urea levels. However, nutrition usually leads to minor deviations from the norm. For example, if a person eats a lot of meat for several days before donating blood for analysis, the urea concentration will be at the upper limit of normal or slightly elevated. Significant deviations (

exceeding the norm by 2–3 times or more

) appear only in the presence of pathological processes.

Is urea found in milk and other foods?

Urea is one of the waste products of living organisms, but normally it is excreted naturally through urine. This substance cannot enter food products. Even if the product is contaminated, it does not affect its nutritional value and does not pose a danger to the body.

Blood urea levels may be affected by foods nutrition , containing a lot of proteins and other nitrogenous substances. That is, after consuming these products, more urea is formed in the body, and its concentration in the blood increases.

Significant amounts of protein are found in the following foods:

• meat;
• Fish and seafood ( shellfish, canned fish, some algae, etc.);
• cheeses;
• milk ;
• cottage cheese, etc.

A number of fertilizers for agricultural crops are obtained from urea, but this substance itself does not enter the plants. It undergoes certain transformations in the soil and in the plant itself, and appears in the final product in the form of certain proteins and amino acids.

Does being overweight affect your urea levels?

There is no direct relationship between excess weight and urea concentration in the blood or urine. Excessive amounts of urea may occur in cases where excess weight is caused by a number of diseases. For example, some patients with diabetes have metabolic disorders. This can affect protein metabolism, kidney function, and the gradual accumulation of excess weight. There are other pathologies that simultaneously cause excess weight and an increase in urea levels. In each specific case, you should contact a specialist who will determine the root cause of these violations.

What diseases cause urea levels to rise?

There are many different pathologies that can lead to an increase in urea levels in the blood and urine. Most often these are kidney diseases or various metabolic disorders. The most pronounced increase is observed in pathologies that cause renal failure.

The level of urea in the blood may be elevated in the following diseases and pathological conditions:

Urea may also increase in other diseases that are less common. Not in every case, increasing urea levels should be given much attention. For example, with burns and large wounds, its level can be significantly exceeded, but special treatment is usually not required. The increase is caused by the breakdown of a large number of cells, which causes a lot of proteins to enter the blood. As the wounds heal, your blood urea levels will drop to normal levels.

Urea is an important diagnostic criterion only for liver and kidney diseases. In this case, based on its level, one can draw indirect conclusions about the severity of the disease and choose treatment tactics ( for example, in renal failure).

An increase in the level of urea in the urine most often appears simultaneously with its increase in the blood. The body tries to get rid of toxins in this way. However, there are a number of pathologies that increase the secretion of urea.

A high concentration of urea in the urine can be observed in the following diseases:

• some pernicious anemias;
• prolonged fever;
• taking thyroxine ( thyroid hormone);
• thyroid diseases leading to thyrotoxicosis (excessive secretion of thyroxine).

Symptoms of high and low urea

Impaired urea excretion, which is accompanied by signs of general intoxication, is called hyperazotemia.. With this deviation, the fluid content in the cells increases, which leads to their dysfunction. The accumulation of ammonia in cellular structures leads to disruption of tissue trophism. Ammonia intoxication in severe situations can cause the development of a coma. In less severe ammonia poisoning, the regulatory function of the central nervous system suffers.
The symptoms of urea intoxication are varied; it largely depends on the level of increase in urea concentration and the individual characteristics of the organism.

The leading symptoms are:

• paleness of the skin;
• signs of general intoxication ( headache , weakness, deterioration in health);
• appearance nausea , vomiting, diarrhea ;
• disturbances in urinary flow (dysuria),
• visual disturbances;
• liver dysfunction.

The presence of the listed symptoms in a patient does not make it possible to identify the root cause of the increase in urea levels and assess the degree of the disorder. Only blood chemistry has real diagnostic value.

The accumulation of urea in the blood is most often not accompanied by any symptoms. This substance does not have significant toxicity, so a slight increase in urea concentration does not affect the patient’s condition. In cases where the urea level is greatly exceeded (

the norm was exceeded several times or more

) a person may experience general symptoms

intoxication

When urea levels are high, the patient experiences the following complaints:

A number of more serious symptoms may also appear, which are associated not so much with increased urea levels, but with pathologies (

usually kidney

) that led to this violation. Most often these are swelling, urination problems, and high blood pressure.

In some cases, the concentration of urea in the blood increases simultaneously with the concentration of other substances. As a rule, this occurs with severe renal impairment. In these cases, the symptoms and manifestations of the disease can be very severe, but their appearance is caused not so much by excess urea in the blood, but by general intoxication and related disorders. In severe cases, patients may vomit, convulsions , diarrhea, bleeding tendency, etc. Without qualified medical care, the patient may fall into a uremic coma .

Does urea have harmful effects on the body?

Urea itself is not a toxic substance and does not have a direct negative effect on the body. That is why it is “used” by the body as a safe form of eliminating more toxic substances (

other nitrogenous compounds

). Most of the symptoms that appear in patients with high urea levels are associated with concurrent intoxication with other substances due to renal failure.

Among the harmful effects of urea itself, one can note the accumulation of fluid in tissues (swelling is possible). This is explained by the fact that urea is an osmotically active substance. Its molecules are able to “attract” water molecules to themselves. At the same time, urea molecules are small and can pass through cell membranes. Thus, with a high concentration of urea, fluid retention in the tissues is possible.

Why are urea and its salts dangerous for gout?

Contrary to popular belief, when gout occurs, it is not urea that is retained in the body, but uric acid, another nitrogen compound. In a healthy body, uric acid does not play a serious physiological role and is of secondary importance. With gout, the salts of this substance begin to accumulate in the tissues with the formation of characteristic foci (

tophi

). Urea is not directly related to the development of this disease.

Is increased urea dangerous in diabetes?

Diabetes mellitus is a serious disease that affects many processes occurring in the body. Patients with this pathology are recommended to regularly undergo blood and urine tests in order to notice deterioration of the condition and various complications in time. In a biochemical blood test, urea can indicate very serious problems. For example, with advanced diabetes mellitus, some patients develop ketoacidosis (

Ketone bodies appear in the blood and the blood pH changes

). As a result, urea levels may begin to rise. Also, with diabetes mellitus, kidney damage is possible (

diabetic nephropathy

). The result may be a deterioration in blood filtration and urea retention in the body.

Thus, elevated urea levels in patients with diabetes usually indicate a worsening of their condition. If you receive such a result, it is recommended to immediately consult your doctor ( endocrinologist) to stabilize the situation.

Treatment for low and high urea

High or low urea itself is not a separate pathology and does not require a special course of treatment. This substance is a kind of indicator that can indicate pathologies of various organs and systems. The doctor will not prescribe treatment based on increased or decreased urea alone. Additional tests are usually required to make a diagnosis.

Most often with increased or decreased urea ( depending on the examination results) begin treatment in the following areas:

• hemodialysis and the administration of drugs to cleanse the blood of toxic breakdown products ( usually in renal failure);
• treatment of causes of renal failure;
• restoration of liver function ( treatment of hepatitis, etc.);
• normalization of hormonal levels ( in case of thyroid dysfunction or pancreas), etc.

Thus, treatment for high urea can be varied and depends on what exactly caused this deviation. Urea itself can be reduced using hemodialysis ( blood filtration using a special device

Urea is the main breakdown product of proteins. It is the chemical form in which nitrogen that the body does not need is removed through urine.

The accumulation of urea and other nitrogen-containing compounds in the blood due to renal failure leads to uremia.

Synonyms Russian

Carbonic acid diamide, urea, urea in the blood.

SynonymsEnglish

Urea nitrogen, Urea, Blood Urea Nitrogen (BUN), Urea, Plasma Urea.

Research method

UV kinetic test.

Units

mmol/l (millimoles per liter).

What biomaterial can be used for research?

Venous, capillary blood.

How to properly prepare for research?

• Do not eat for 12 hours before the test.
• Avoid physical and emotional stress and do not smoke 30 minutes before the test.

General information about the study

Urea is one of the end products of protein metabolism, containing nitrogen. It is produced in the liver, transported by the blood to the kidneys, where it is filtered through the glomerulus and then excreted. The blood urea test result is an indicator of glomerular production and urine excretion.

Metabolized nitrogen is found in the body in the form of ammonia, produced from the remains of protein breakdown and processing. Ammonia in the liver combines with carbon dioxide to form urea. Rapid protein breakdown and kidney damage rapidly raise blood urea levels (as does virtually any massive cell death).

The amount of urea released is directly dependent on the level of protein consumed by a person; the reasons for an increase in urea in the blood are feverish conditions, complications of diabetes, and increased hormonal function of the adrenal glands. Elevated urea levels are a marker of decreased glomerular filtration.

Urea is one of the main metabolites in the blood; the body does not use it in any way, but only gets rid of it. Since this excretion process is continuous, a certain amount of urea is normally always present in the blood.

The level of urea should be interpreted inseparably from creatinine values. The term "uremia" is applied when the level of urea in the blood rises above 20 mmol/l.

Azotemia, also indicated by an increase in urea concentration, is most often a consequence of inadequate excretion due to kidney disease.

Blood urea levels decrease in many liver diseases. This occurs due to the inability of damaged liver cells to synthesize urea, which in turn leads to increased ammonia concentrations in the blood and the development of hepatic encephalopathy.

Renal failure occurs when the glomerulus loses its ability to filter blood metabolites through itself. This can occur suddenly (acute renal failure) in response to illness, administration of drugs, poisons, or injury. Sometimes this is a consequence of chronic kidney diseases (pyelonephritis, glomerulonephritis, amyloidosis, kidney tumors, etc.) and other organs (diabetes, hypertension, etc.).

A urea test is usually ordered in combination with a blood creatinine test.

What is the research used for?

• To assess kidney function in a range of conditions (in conjunction with a creatinine test).
• For the diagnosis of kidney disease and for checking the condition of patients with chronic or acute renal failure.

When is the study scheduled?

• Urea is tested during a biochemical study:
  • for nonspecific complaints,
  • when assessing renal function before prescribing drug therapy,
  • before hospitalization of a patient due to an acute illness,
  • when a person is in a hospital.
• For symptoms of kidney dysfunction:
  • weakness, fatigue, decreased attention, poor appetite, sleep problems,
  • swelling of the face, wrists, ankles, ascites,
  • foamy, red or coffee-colored urine
  • decreased diuresis,
  • problems with urination (burning, intermittency, predominance of nocturnal diuresis,
  • pain in the lumbar region (especially on the sides of the spine), under the ribs,
  • high pressure.
• In addition, this analysis can be carried out periodically:
  • to check the condition of patients with chronic kidney disease or non-renal chronic diseases such as diabetes, congestive heart failure, myocardial infarction, arterial hypertension, etc.,
  • before and during drug therapy to determine the state of kidney function,
  • after dialysis sessions to assess their effectiveness.

What do the results mean?

Reference values:

Reasons for increased urea levels in the blood:

• decreased renal function caused by congestive heart failure, loss of salts and fluids, shock in combination with excessive protein catabolism (gastrointestinal bleeding, acute myocardial infarction, stress, burns),
• chronic kidney disease (pyelonephritis, glomerulonephritis, amyloidosis, renal tuberculosis, etc.),
• obstruction of the urinary tract (bladder tumor, prostate adenoma, urolithiasis, etc.),
• bleeding from the upper gastrointestinal tract (peptic ulcer of the stomach, duodenum, cancer of the stomach, duodenum, etc.),
• diabetes mellitus with ketoacidosis,
• increased protein catabolism in cancer,
• taking corticosteroids, nephrotoxic drugs, tetracyclines, excess thyroxine,
• use of anabolic steroids,
• food high in protein (meat, fish, eggs, cheese, cottage cheese).

Reasons for low urea levels in the blood:

• liver failure, some liver diseases: hepatitis, cirrhosis, acute hepatodystrophy, liver tumors, hepatic coma, poisoning with hepatotoxic poisons, drug overdose (this disrupts urea synthesis),
• acromegaly (a hormonal disease characterized by increased production of somatotropic hormone),
• fasting, low protein diet,
• impaired intestinal absorption (malabsorption), for example, with celiac disease,
• nephrotic syndrome (increased protein excretion in the urine, hyperlipidemia, decreased protein levels in the blood),
• increased production of antidiuretic hormone (ADH) and, as a consequence, pathological hypervolemia,
• pregnancy (increased protein synthesis and increased renal filtration cause a decrease in the amount of urea in pregnant women).

What can influence the result?

The main groups of methods for determining urea content are divided into:

1. Xanthhydrols: The heterocyclic alcohol xanthhydrol reacts with urea to form insoluble dixanthylurea, which is further determined gravimetrically, nephelometrically, colorimetrically or titrimetrically. The methods are accurate, but labor-intensive.
2. Hypochlorite – B.A. Rashkovan’s method, which consists in the appearance of a characteristic color during the interaction of urea with sodium hypochlorite and phenol, is practically not used due to the different shade of experimental and control samples, and the frequent appearance of turbidity when adding HCl.
3. Diacetyl monooxime the methods are based on the Firon reaction - the interaction of urea and diacetyl monooxime with the formation of colored products, they are characterized by good reproducibility, high sensitivity, and high specificity.
4. Semi-quantitative methods using indicator paper.
5. Methods using ion selective electrodes.
6. Enzymatic methods are based on the hydrolysis of urea by urease (optimum pH 6.0-8.0). The resulting ammonia is determined using various reactions (phenol hypochlorite, glutamate dehydrogenase, salicylate-hypochlorite).
7. Gasometric(hypobromite), based on the oxidation and decomposition of urea with sodium hypobromite in an alkaline environment:

CO 2 (NH 2) + 3NaBrO → N 2 + CO 2 + 3NaBr + H 2 O

The released carbon dioxide is absorbed by the solution, leaving only nitrogen free, the volume of which is measured. The method is nonspecific (since hypobromite reacts not only with urea, but also with other substances containing amino groups), inaccurate, poorly reproducible and labor-intensive.

As unified Methods for determining urea have been approved: phenol hypochlorite, diacetyl monooxime and urease methods, and an express method using Ureatest indicator paper.

Determination of urea in blood serum and urine with diacetyl monooxime

The methods of this group are based on the Fearon reaction, which occurs in two stages. The first step is the hydrolysis of diacetyl monooxime to form diacetyl and hydroxylamine. In the second step, hydroxylamine reacts with urea to form a colored diazine derivative. For the oxidation of hydroxylamine, the following can be used: sodium persulfate, arsenic acid, perchloric acid, phenazone, cations. To intensify color and its stability, the following are used: thiosemicarbazide, phenylanthranilic acid, glucuronolactone, cations, tryptophan, nitrites.

Determination of urea by the urease method

Enzymatic methods are based on the hydrolysis of urea by urease in an incubation medium with pH = 6.0‑6.5 (EDTA buffer) or pH = 6.9‑7.0 (phosphate buffer) into carbon dioxide and ammonia. The resulting ammonia can be determined by a highly sensitive and specific reaction with phenol hypochlorite and the catalyst nitroprusside, by a salicylate-hypochlorite reaction, by a reaction with Nessler’s reagent (it is 10 times less sensitive compared to phenol hypochlorite, low specificity), by a dichloroisocyanurate reaction (the presence of protein interferes with the determination) .

Normal values

If it is necessary to compare the concentration of residual nitrogen with the nitrogen content of urea, the concentration of the latter should be divided by 2.14.

Influencing factors

• in vivo: increase - nephrotoxic drugs, corticosteroids, excess thyroxine; decrease - increase in the concentration of somatotropic hormone,
• in vitro: reduction (urease method) – sodium citrate.

Clinical and diagnostic value

Serum

The level of urea depends on the rate of its synthesis in the liver and excretion through the kidneys, as well as on the amount of protein catabolism.

Increased urea levels may occur with impaired renal function (acute and chronic diseases, urinary tract obstruction), impaired renal perfusion (congestive heart failure), depletion of body water (vomiting, diarrhea, increased diuresis or sweating), increased protein catabolism (acute myocardial infarction, stress, burns, yellow liver atrophy, gastrointestinal bleeding), with a high protein diet. In severe cases of acute renal failure, a 10-fold increase in urea levels was detected. Since the water-excreting function of the kidneys is restored faster than the concentration ability, normal excretion of urea in the urine occurs much later than the restoration of diuresis.

A decrease is observed with a low protein diet, with increased protein utilization in tissues (late pregnancy), severe liver diseases accompanied by impaired urea synthesis (parenchymal jaundice, liver cirrhosis).

Urine

An increase in the amount of urea in the urine is associated with hyperthyroidism, pernicious anemia, fever, phosphorus poisoning, observed with a high protein diet, and in the postoperative period.

The decrease is observed in patients with nephritis and other kidney diseases, uremia, parenchymal jaundice, cirrhosis or liver dystrophy, also in healthy growing children and on a low-protein diet.

Increase content urea in the blood observed when:

· increased its formation as a result of a diet rich in proteins, excessive protein catabolism, leukemia, jaundice, severe infectious diseases, intestinal obstruction, burns, dysentery, shock;

· decreased urinary excretion with retention renal azotemia, retention extrarenal azotemia (acute renal failure, tumors of the urinary tract, prostate gland, nephrolithiasis, cardiac failure);

· bleeding from the upper gastrointestinal tract;

· taking certain medications - sulfonamides, levomecithin, tetracycline and others.

Decline content urea in the blood observed when:

· especially severe liver damage, in particular with phosphorus, arsenic poisoning, decompensated cirrhosis;

· fasting;

· reduced protein catabolism;

· after administration of glucose;

· after hemodialysis.

Increase excretion urea in urine observed when:

· pernicious anemia (due to negative nitrogen balance);

· fever;

· after taking medications (salicylates, quinine, etc.);

· hyperprotein diet;

· hyperfunction of the thyroid gland;

· in the postoperative period.

Decrease excretion urea in urine observed when:

· nephritis, uremia;

renal dysfunction;

Nephropathy in pregnant women;

parenchymal jaundice (due to impaired urea formation);

acute liver dystrophy;

· progressive cirrhosis of the liver;

· taking anabolic hormones (positive nitrogen balance).

Answer the questions:

1. Define the concepts of nitrogen balance, residual nitrogen, residual nitrogen, azotemia.

2. Name the causes and types of azotemia.

3. Why does the concentration of urea in the blood increase with lesions of the cardiovascular system? What type of azotemia does this change relate to?

4. To diagnose which diseases, the level of urea in the blood and urine is most often examined?

5. What is the excretory capacity of the kidneys?

6. How can the level of urea serve to diagnose disorders of the excretory capacity of the kidneys?

Practical work

"Determination of creatinine in blood serum by the Jaffe method."

Objectives of practical work:

· consolidate knowledge about residual blood nitrogen, azotemia;

· learn to examine the creatinine content in blood serum.

Tasks for independent work:

1. Copy the principle and methodology of practical work into your notebook.

2. Set up a workplace for practical work.

3. Do practical work.

4. Make the necessary calculations.

6. Draw a conclusion on the work and drawings.

7. Answer additional questions.

Principle:

In an alkaline environment, creatinine forms a yellow-red complex compound with picric acid (Jaffe reaction). The color intensity is proportional to the concentration of creatinine in the test sample.

Determination progress:

· Carry out deproteinization (in a centrifuge tube).

· Mix the mixture thoroughly and centrifuge at 1500 rpm for 15 minutes.

· Analyze the centrifugate using the Jaffe reaction according to the table.

· Mix the mixture thoroughly and keep at room temperature for 20 minutes.

Measure the optical density of the test sample ( E1) and calibration sample ( E2) relative to the control sample at a wavelength of 520 nm (500-560 nm) in a cuvette with an optical path length of 5 cm.

Calculation the amount of creatinine is calculated according to the formula:

C= E1 / E2 * 353.6 µmol/l

C= E1 / E2 * 40 mg/l.

Norm:

In blood serum: in men 44-100 µmol/l,

in women 44-88 µmol/l.

In daily urine: 4.4-17.7 mmol.

Notes:

1. When using urine as a sample, it is first diluted 1:100, and the result is multiplied by 100.

2. If necessary, the quantities of the test material and reagents can be changed proportionally.

3. It is mandatory to use a calibration sample for each series of analyses.