the relevance of the concentration of ammonium in the blood


Ammonemia indicates the concentration of ammonium in the blood, which is a nitrogenous product originating mainly from the metabolism of food proteins and intestinal bacterial fermentation

The process by which ammonium is produced from proteins is the deamination of individual amino acids which lose their amine group (NH2).

Ammonium in the blood comes from the metabolism of amino acids described above, but also from the metabolism of amines and the absorption, in the large intestine, of ammonia resulting from the degradation of amino acids and urea (food or blood in the case of haemorrhage) by the local bacterial flora.

A significant proportion of ammonium is also formed in the kidney

Since ammonia is a toxic metabolite for the central nervous system, it must be quickly transformed into urea by the liver, via the so-called urea cycle, then eliminated with the urine.

Problems such as liver failure and congenital enzyme defects can impair this transformation, causing serious damage to the body.

The ammonia assay is performed on a blood sample taken from a peripheral vein, usually in the arm

The blood sample is then placed in a test tube containing an anticoagulant (EDTA), which is kept cold.

There are mainly two methods for measuring the ammonium concentration: the enzymatic method, which uses blood plasma by centrifugation, where the plasma must be absolutely free of hemolysis, and the “dry” chemistry method, which is based on the principle of micro-diffusion of a drop of whole blood.

The ammonium ion it contains is transformed into ammonia gas, which will react to develop a color directly proportional to the amount of ammonium present.

The dosage of ammonia is most often necessary to assess the degree of liver damage in the event of severe liver disease, in the presence of renal insufficiency or in the face of certain rare genetic diseases, such as those linked to the absence of synthesis of urea cycle enzymes.

It may also be necessary when altered behaviors and states of consciousness that can go as far as coma are observed in the patient.

Thus, ammonia is useful when, for example, an infant exhibits frequent vomiting and lethargy, or if a child has continuous vomiting and abnormal sleepiness.

It is a useful parameter for the diagnosis of hepatic encephalopathy and for the diagnosis of Reye’s syndrome, a very rare but potentially fatal syndrome that causes inflammation and edema of the brain and degeneration of the liver.

The blood sample must be taken without venous stasis, possibly on an empty stomach, except in an emergency.

The blood sample should be placed in a test tube with an anticoagulant and immediately afterwards either immersed in a bath containing water and ice, or transported in a polystyrene container with a siber.

It must reach the laboratory immediately; all this to slow down the neoformation of ammonium that would occur over time at room temperature.

Factors to avoid that can lead to increased values ​​include: very intense muscular effort, a diet that is too high in protein, parenteral (intravenous) nutrition, smoking, alcohol abuse, certain medications including acetazolamide, furosemide, barbiturates, isoniazid, valproic acid.

Reduced values ​​may result from: low protein (protein deficient) diets, medications, such as certain broad-spectrum antibiotics, lactulose, levodopa and potassium salts.

Normal values ​​vary depending on the method used.

The microdiffusion method has normal values ​​from 0 to 75 µg/dL, the enzymatic method should be below 100 µg/dL.

Increased levels of ammonium in the blood indicate that normal metabolism, and therefore normal elimination of ammonium from the body, is not occurring.

In newborns, this can occur in the event of a defect in one of the enzymes of the urea cycle, as well as in the course of hemolytic disease of the newborn.

As already mentioned, an increase in the level of ammonia is useful in the diagnosis of Reye’s syndrome, which usually occurs in infants as a result of a viral illness (influenza, chickenpox) aggravated by the use of aspirin.

A previously undiagnosed hereditary defect in the urea cycle can also be detected in children.

In general, it can be said that in children and adults, high concentrations of ammonium can indicate damage to the liver or kidneys.

Elevated blood ammonium levels may be common in severe stomach or intestinal bleeding due to protein release from blood cells, in heart failure, in decreased liver perfusion, in acute leukemia, and in metabolic alkalosis.

A decrease in the level of ammonia can be observed in hypertension, during the use of certain antibiotics (neomycin) and following a low protein diet.

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Source:

Bambino Gesu

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