Azotemia: what values indicate a kidney problem?

It is a blood parameter, normally included in routine tests, useful for assessing kidney function and protein metabolism.

All tests ending with “emia” indicate the dosage of a certain biochemical parameter in the blood. Azotemia is therefore the concentration of non-protein nitrogen present in the circulation. What is the use of knowing this value? What is its normal range? And what other surveys should be combined for a full evaluation? Through the answer to these guiding questions we try to understand the usefulness and meaning of azotemia; an analysis for which a simple venous sampling is necessary, usually carried out by an arm, and which does not require special preparation (except to be fasting, a condition that is necessary for most blood tests).

Where nitrogen comes from

Depending on the process in which it is involved, nitrogen is distinguished into protein and non-protein. The one measured through the examination of azotemia – that is, the non-protein nitrogen present in the blood – is the waste product of protein metabolism, one of the fundamental macronutrients for the proper functioning of the body (together with carbohydrates and lipids). Since one of the main tasks of the kidneys is to dispose of waste, it is inevitable that an increase in azotemia, both in humans and animals, is an important indicator of their possible dysfunction.

This parameter therefore provides double information: on the one hand it expresses efficiency or, as they say, renal function; on the other hand, in case of increase, it is an alarm light, as its constant and uncontrolled increase leads to coma.

The main source of nitrogen is proteins introduced with food: a part of them (or rather of their components, amino acids) is used by the body to manufacture new proteins, while what is not needed is degraded by the liver. The resulting nitrogen is eliminated in the form of ammonia which, as toxic to the body, is in turn transformed into urea.

On the results of the examinations, the analysis laboratories can report two possible indications, which it is good to know to avoid confusion: the actual azotemia, whose normal value is between 22 and 46 mg / dl of blood (with variations related to age and sex), and urea nitrogen (or BUN, from the English blood urea nitrogen), ranging from 10.3 to 21.4 mg/dl. The reference values are usually also reported on the report.

Possible meanings of increase and decrease

It should be noted that hyperazotemia, i.e. exceeding the limit value, is not always synonymous with nephropathy (kidney disease).

This increase can in fact also be promoted by a high-protein diet (ie rich in protein) or fasting (which forces the body to destroy proteins for energy), or it can be associated with various physiological and non-physiological situations, including:

  • pregnancy;
  • muscle overwork (often due to intense physical activity);
  • reduced blood flow due to bleeding, heart failure or extensive burns;
  • Trauma;
  • kidney stones (presence of stones in the kidneys);
  • cirrhosis (a disease that involves altering the structure of the affected tissues, often hepatic tissues, compromising their functionality);
  • gout (a disease that affects the joints and surrounding tissues causing inflammation);
  • dehydration (i.e. the lack of water in the body due to its excessive loss or inadequate intake of liquids and / or food);
  • decompensated diabetes;
  • cortisone therapies.

In other words, azotemia can increase either due to decreased renal filtration or increased urea production or due to obstruction of urinary flow. Its decrease, on the contrary, correlates with malnutrition (poor protein intake), liver failurepoisoning.

Azotemia is therefore a routine examination, almost always prescribed as part of a normal control. It is, then, further justified in the presence of:

  • joint or muscle pain;
  • pain in the bones;
  • back pain;
  • sense of heaviness in the legs;
  • drowsiness, tiredness and exhaustion;
  • decreased appetite;
  • arterial hypertension (the so-called “high blood pressure”);
  • itch;
  • swelling (especially of hands and feet);
  • jaundice (yellowish pigmentation of the skin and whites of the eyes, due to an excess of bilirubin in the blood);
  • fatigability;
  • urinary disorders (such as the presence of abnormalities in the urine, the need to urinate often, or the evacuation of more urine than normal),
  • vomit;
  • inextinguishable thirst.

Other useful exams

Azotemia, alone, may not be sufficient: for example, a value could be “falsely normal” in an individual who, despite kidney damage, takes little protein or is in a condition of overhydration.

That is why another test that the doctor usually prescribes in association with azotemia is the measurement of creatinine levels (or rather creatininemia, normally between 0.7 and 1.4 mg / dl). It is a waste product of muscle metabolism (and, specifically, the result of the degradation of phosphocreatine, a protein essential for muscle activity), which is why it is appropriate to abstain from physical exercise in the two days prior to the collection. Creatinine is a reliable indicator of kidney function: the urea/creatinine ratio is normally between 20 and 30 and its increase is suggestive of dehydration.

The two tests are usually used to monitor patients with renal insufficiency (acute or chronic) or undergoing dialysis (a medical procedure that serves to remove unwanted substances from the body that are generally eliminated by the kidneys).

A further important examination is uricemia, that is, the concentration of uric acid in the blood, useful in the suspicion of gout and nephropathy. Finally, if creatinine and uricemia are normal, it can reasonably be excluded that a hyperazotemia is of renal origin.

Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.

The blog covers a wide range of topics related to health and wellness, with articles organized into several categories.

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