Generality
Ammonemia is a medical term that indicates the concentration of ammonia in the blood .
Ammonia is a nitrogenous product that is formed in the body by the activity of many tissues, but for the most part comes from the metabolism of dietary proteins and from intestinal bacterial fermentations.
Ammonia is a metabolite toxic to the central nervous system and must be rapidly transformed into urea by the liver.
In most cases, increases in ammoniama depend on severe liver failure or some congenital enzyme defects.
What's this
Ammonia: Biological Role
A fundamental phase of protein metabolism is deamination, during which the individual amino acids are deprived of the amino group (NH 2 ). The remaining part of the molecule, called alpha-keto acid, can be used for energy purposes or for glucose synthesis. The amino group is instead transferred to the alpha-ketogluatarate (intermediate of the Krebs cycle), with formation of glutamate; the latter undergoes an oxidative deamination in the mitochondrial matrix, with production of free ammonia (NH 3 ).
Ammonia is a toxic molecule, especially for the brain.
Fortunately, a healthy organism is perfectly capable of incorporating ammonia into non-toxic compounds, which also constitute its form of transport and pre-elimination.
Ammonia, therefore:
- It can be added to alpha-ketogluatarate to reform glutamate
- It can be incorporated into the glutamate molecule to give glutamine
- It can be directed to the synthesis of carbamyl phosphate. This reaction is a prelude to the so-called urea cycle, which in the liver leads to the transformation of ammonia into the non-toxic urea molecule, which is then eliminated in the urine.
Ammonemia: ammonia in the blood
The ammonia present in the blood derives from the metabolism described above of the amino acids, but also from that of the amines and from the absorption in the large intestine of the ammonia deriving from the degradation of the amino acids and urea (food or blood in case of hemorrhage) by the flora local bacterial.
An important amount of ammonia is also formed at the kidney level; here, in fact, there are particularly high concentrations of glutaminase, a mitochondrial enzyme that hydrolytically dames glutamine to glutamic acid and ammonia. The latter passes into the luminal liquid and is protonated to ammonium ion (NH 4 +), then eliminated in the urine. This mechanism, given the conspicuous elimination of H + hydrogenions (NH 3 + H + → NH4 +), is very important for maintaining the body's acid base balance.
Why do you measure
The determination of ammoniama is mainly used as a support in the diagnosis of serious liver diseases and to understand the reason for alterations of states of consciousness .
This test can be prescribed, along with other tests (such as glucose, electrolytes and kidney and liver function tests), to define the cause of a coma of unknown origin or to support the diagnosis of Reye's syndrome or hepatic encephalopathy.
Ammoniaemia may also be required to support the diagnosis and assess the severity of some metabolism disorders involving the urea cycle .
Normal values
NORMAL VALUES OF AMMONEMIA IN THE ADULT (slightly variable from laboratory to laboratory):
21 - 50 µmol / l (15 - 60 µcg / 100 ml).
High Ammonemia - Causes
An increase in ammonia in the blood is often a sign of an altered metabolism in the liver .
Situations of hyperammonemia are found, for example, in cases of severe liver damage with organ failure, as occurs in advanced cirrhosis or during important hepatitis.
High blood levels of ammonia are also common during:
- Hepatic failure;
- Severe bleeding of the stomach or intestines;
- Heart failure;
- Reduced hepatic perfusion;
- Congenital defects of enzymes that intervene in the urea cycle:
- Acute leukemia;
- Metabolic alkalosis;
- Reye syndrome;
- Hemolytic disease of the newborn;
- Circulatory alterations involving a direct passage of blood from the portal venous system to the general venous system.
High concentrations are also recorded in the event of:
- High-protein diets;
- After intense physical exercise (especially in males and bodybuilders, due to greater muscle mass);
- Dysbiosis.
Among the drugs able to increase the values of ammonia, we recall:
- Acetazolamide;
- Valproic acid;
- Furosemide;
- Etacrinic acid;
- chlorthalidone;
- Isoniazid.
Cigarette smoking also sharply increases the values of ammonia (+ 10 µmol / l after a cigarette).
Symptoms Hyperammonemia
- He retched;
- Meat waste;
- Ataxia;
- Lethargy;
- Mental delay;
- Disorientation (which in extreme cases proceeds to coma and death).
However, it is good to point out that ammoniama is only roughly related to the severity of brain damage. Therefore, people with high levels of ammoniama may not show any signs of altered brain function, and vice versa. The use of this test in the diagnosis and monitoring of hepatic encephalopathy remains controversial to this day.
The doctor may prescribe the ammoniemia test in the presence of the symptoms described above or if you suspect, in the child, the presence of Reye's syndrome or a congenital metabolic defect of the urea cycle.
Low Ammonemia - Causes
Low levels of ammonium in the blood can be the consequence of diets particularly poor in proteins or in the use of drugs capable of lowering ammonia, such as Levodopa, Lattulose, Neomycin, Lactobacillus, Kanamycin.
How to measure it
For the evaluation of ammonia, the patient must undergo blood sampling.
Preparation
See also: Drugs for the treatment of hyperammonemia
The sample is usually taken in the morning. Your doctor will suggest if you need to observe a fast at least 8 hours before the exam.
For a correct interpretation of the results it must be kept in mind that the values of this analysis can be influenced by some particular conditions, such as, for example, by a high-protein diet and by the practice of intense physical exercise.
Interpretation of Results
Significantly increased levels of ammonia in the blood indicate that the body is not actually metabolizing and eliminating the metabolite, but does not indicate its cause.
- In newborns, extremely high levels are associated with a hereditary deficiency or defect of urea cycle enzymes, but can also be observed in hemolytic disease.
- In adults, high ammonium concentrations may also indicate liver or kidney damage.
- High levels may also indicate an enzymatic defect of the urea cycle not previously diagnosed.
