1. Urea cycle

 Low blood urea nitrogen   |   Level of ammonia |  


The urea cycle, also known as the ornithine cycle, is a metabolic pathway that takes place in the liver and is responsible for the elimination of excess nitrogen in the body. Nitrogen is a byproduct of protein metabolism and is toxic to the body in high concentrations.

The urea cycle converts ammonia, which is produced when proteins are broken down, into urea, which can be safely excreted by the body through urine. The urea cycle consists of several enzymatic reactions that take place in the mitochondria and cytoplasm of liver cells.

The steps involved in the urea cycle are as follows:

The amino acid, ornithine, reacts with ammonia to form citrulline.
  1. Citrulline combines with aspartate to form argininosuccinate.
  2. Argininosuccinate is cleaved into arginine and fumarate.

    Urea cycle

  3. Arginine is hydrolyzed by the enzyme arginase to form urea and ornithine.
  4. Ornithine then re-enters the cycle, and the process starts again.

The urea cycle is essential for the normal functioning of the body, and defects in the cycle can lead to a variety of diseases, including hyperammonemia, a condition in which there is too much ammonia in the blood. Treatment for these conditions often involves the restriction of dietary protein and the use of medications to control ammonia levels in the blood.

2. Low blood urea nitrogen

Low blood urea nitrogen (BUN) levels can be caused by a variety of factors

  1. Low protein diet: BUN is a byproduct of protein metabolism, so a diet low in protein can result in low BUN levels.
  2. Liver disease: The liver is responsible for producing urea, so any damage or disease affecting the liver can result in decreased urea production and low BUN levels.
  3. Pregnancy: During pregnancy, blood volume increases, which can dilute the blood and lower BUN levels.
  4. Malnutrition: Malnutrition, especially protein malnutrition, can lead to low BUN levels.
  5. Overhydration: Drinking too much water or receiving too much intravenous fluid can result in low BUN levels due to dilution of the blood.
  6. Certain medications: Some medications, such as diuretics and steroids, can lower BUN levels.

Low BUN levels are not usually a cause for concern, as long as other laboratory values are normal and the individual is not experiencing symptoms. However, in some cases, low BUN levels can indicate a serious underlying medical condition, such as severe liver disease or malnutrition, and further evaluation may be necessary. It is important to discuss any concerns about BUN levels with a healthcare provider.

3. Level of ammonia in the body 

Ammonia is a waste product that is produced by the breakdown of protein in the body. It is primarily produced in the liver and is excreted

from the body in the form of urea. The normal range for blood ammonia levels is 15 to 45 micrograms per deciliter (µg/dL) or 11 to 32 micromoles per liter (µmol/L). However, ammonia levels can vary depending on several factors, including age, diet, and overall health.

Abnormally high levels of ammonia in the blood, known as hyperammonemia, can be indicative of liver disease, kidney failure, or certain metabolic disorders. Symptoms of hyperammonemia can include confusion, fatigue, nausea, vomiting, and tremors.


The normal range of ammonia levels in the blood typically varies depending on the laboratory performing the test and the method used to measure it. However, generally accepted normal ranges are:

  • For adults: 15-45 micrograms per deciliter (mcg/dL) or 11-32 micromoles per liter (µmol/L)
  • For newborns: less than 100 mcg/dL or less than 74 µmol/L

It’s worth noting that ammonia levels can fluctuate throughout the day and can be affected by factors such as diet, medications, and underlying medical conditions

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