Generality
The azotemia measures the amount of total non-protein nitrogen present in the blood. Much of this nitrogen is contained in the molecules of urea, a molecule harmless to our body, which derives from the organic transformation of ammonia.
Normal blood urea levels are between 15 and 50 mg / dl (milligrams per deciliter of blood), with a variability that depends on age and sex. Values different from the reference ones indicate an imperfect purification of blood by the kidneys.
Typical conditions of hyperazotemia can be found mainly in the presence of decreased functionality of the kidneys. This may be due to dehydration or heart failure, acute or chronic renal disease, a high-protein diet and therapies with toxic drugs on the liver.
A decrease in blood urea nitrogen values can be determined by dietary regimes that are too low in protein or carbohydrates, liver failure, poisoning and nephrosis.
What's this
Nitrogen is a laboratory parameter that expresses the concentration of non-protein nitrogen in the blood.
Among the various renal functions, there is also the excretion of metabolic waste products, deriving from protein demolition. The main product of hepatic catabolism of exogenous (food) and endogenous (tissue) proteins is urea. The dosage of this metabolite has been used as an indicator of renal function since 1903.
Thanks to the kidneys, much of the urea is eliminated in the urine, while a small amount is reabsorbed at the tubular level.
In the presence of reduced kidney function, the body is unable to eliminate nitrogenous wastes from the protein catabolism from the blood. The resulting accumulation in the bloodstream is responsible for the increased azotemia (hyperazotemia).
Why do you measure
The measurement of azotemia is routinely required in control analyzes.
Together with the creatinine dosage, the results of this examination are considered an index of renal function .
The exam is indicated in the presence of:
- Non-specific malaise;
- Signs or symptoms that suspect some renal alteration;
- Chronic diseases such as diabetes and heart failure (checks at regular intervals).
Furthermore, azotemia can be prescribed by a doctor in order to:
- Evaluate if the kidneys work before starting certain drug therapies;
- Monitor the effectiveness of dialysis or other treatments in patients with chronic and acute kidney disease.
Normal values
In healthy adults, in normal conditions and in the presence of a balanced diet, azotemia varies in the range 22-46 mg / dl.
This figure refers to the plasma concentration of urea.
Some laboratories use different analytical methods, referring to the concentration of urea nitrogen (BUN) which constitutes about half of the urea molecule. In this case the physiological values of azotemia are in the range of 10.3 to 21.4 mg / dl.
High azotemia - Causes
A high blood urea nitrogen rate is not necessarily a sign of reduced kidney function. Regardless of the efficiency of these organs, many people who follow a high-protein or ketogenic diet, will probably have discovered that they have levels of azotemia that are close to, or even higher than, the maximum value considered normal. The phenomenon is more evident when the water supply is reduced.
On the contrary, the high synthesis of protein metabolites can be compensated for by an abundant intake of liquids which, leading to polyuria, on the one hand increases the urinary elimination of urea and on the other lowers the plasma concentration of the metabolite.
Main causes of hyperazotemia
Azotemia values higher than normal can be caused by:
- Acute or chronic kidney disease (such as chronic glomerulonephritis and pyelonephritis);
- Urinary tract obstruction (eg kidney stones);
- Reduced blood supply to the kidneys (eg heart failure, shock, burns, bleeding and trauma).
Other conditions that can increase azotemia include:
- High-protein diets;
- Fasting;
- Sports or work activity that causes a noticeable muscle catabolism (the body uses proteins as an energy source);
- Pregnancy (due to the increased demand for protein);
- Some serious infectious diseases (leptospirosis, renal tuberculosis and pyelonephritis);
- Cirrhosis;
- Gout;
- Therapies with drugs that increase catabolism (for example: cortisone drugs)
- Gastrointestinal bleeding;
- Decompensated diabetes;
- Dehydration (profuse vomiting or diarrhea, poor fluid intake, heart failure, sweating, intense physical activity, etc.);
- Extensive burns.
Low azotemia - Causes
Lower azotemia values than normal are not very common.
However, these can be found in the presence of:
- Some liver diseases (eg hepatitis and severe liver failure);
- nephrosis;
- Excess hydration;
- Low-protein diet;
- Prolonged fasting;
- Pregnancy;
- Malnutrition.
How to measure it
The examination is carried out by means of a simple blood test. The sample is taken from the vein of an arm.
To decrease the risk of false positives and false negatives, doctors and laboratory technicians resort to auxiliary tests (to verify the actual presence of a problem at the kidney level). For example, a dehydration hyperazotemia can be unmasked by the simultaneous increase in the urea / creatinine ratio, normally 20-30. Furthermore, if creatinine levels and uricemia are normal, hyperazotemia is unlikely to be of renal origin.
Preparation
The sample is usually taken in the morning. Your doctor will suggest if you need to be fasting.
Since the plasma and urinary levels of creatinine also increase in relation to physical activity, the amount of muscle mass and protein intake, in the days preceding the examination it is a good rule to stop exercising and follow a diet that provide the right amount of fluids and proteins.
Interpretation of Results
For a correct interpretation of the azotemia results, it must be kept in mind that the values of this analysis can be influenced by some particular conditions, such as, for example, from:
- Dehydration situation (which can be caused by feverish states);
- Amount of proteins present in the diet.
Most kidney or liver diseases can alter blood urea levels.
- IPERAZOTEMIA - The azotemia increases if the liver produces more urea or if the kidneys filter less. Values higher than normal in the blood are mainly found in the presence of chronic glomerulonephritis, pyelonephritis, obstructions of the urinary tract, acute and chronic nephritis up to kidney failure with urination blockage (anuria). Hyperazotemia can also be associated with dehydration or heart failure, a diet rich in proteins, pregnancy and therapies with toxic drugs on the liver.
- HYPOAZOTEMIA - A decrease in azotemia occurs above all in the case of malnutrition (dietary regimes that are too poor in proteins or carbohydrates), liver failure and poisoning.
In any case, for a more detailed investigation, the azotemia must always be accompanied by the request for creatinemia .
Causes of High and Low Azotemia | |
Factors that increase azotemia | Factors that lower azotemia |
High protein diet | Hypoprotein diet |
Dehydration (copious diarrhea, profuse sweating, heart failure, shock, continuous physical activity, etc.). | overhydration |
Fasting, prolonged physical activity | Severe hepatic failure |
Hyperazotemia risk with absolutely healthy and functioning kidneys | Normoazotemia risk in the presence of renal damage |
