The key difference between blood urea nitrogen and blood urea is that blood urea nitrogen measures the amount of nitrogen in urea that is present in the blood, while blood urea is the measurement that deduces the total amount of urea in the blood.
During protein metabolism, degradation and removal of remnants of protein metabolism, especially the nitrogenous components from the system, often lead to toxicity. At present, urea is the main nitrogenous excretory matter in mammals. Urea toxicity rate is much slower in comparison to ammonium. They also have glycoprotein receptors that can further identify the host through complementary receptor-mediated binding.
CONTENTS
1. Overview and Key Difference
2. What is Blood Urea Nitrogen
3. What is Blood Urea
4. Similarities Between Blood Urea Nitrogen and Blood Urea
5. Side by Side Comparison – Blood Urea Nitrogen vs Blood Urea in Tabular Form
6. Summary
What is Blood Urea Nitrogen?
Blood urea nitrogen is the amount of urea nitrogen present in the blood. It refers to the amount of nitrogen present in urea that is released to the blood. Urea is the final nitrogenous excretory matter produced in mammals. Therefore, the main constituent of urea is nitrogen. Urea formation occurs through the urea cycle that takes place in the liver primarily.
Figure 01: Nitrogen Wastes
The recommended normal range of blood urea nitrogen in a healthy individual is 6 mg/dL – 20 mg/dL. However, metabolic complications and dietary modifications can alter the level of blood urea nitrogen. If you follow a high protein diet, you can observe higher blood urea nitrogen. This is mainly to prevent the accumulation of nitrogen in the system following a high protein diet as the accumulation of nitrogen could lead to toxicity.
Furthermore, increased catabolic rates or muscle breakdown, decreased rates of glomerular filtration in the kidney and the decrease of blood volume can also result in elevated levels of blood urea nitrogen. In contrast, a low level of blood urea nitrogen can be observed during a liver malfunction, increased anabolic reactions or formation of muscle mass. Therefore, ideally in growing children, the blood urea nitrogen levels are lower compared to that of an adult.
What is Blood Urea?
Blood urea refers to the concentration of urea in the blood. Urea is the main nitrogenous excretory matter in mammals, including humans. They have a higher nitrogen composition in comparison to the other nitrogenous waste compounds such as uric acid and ammonium. The production of urea takes place in the liver. Primarily, urea production begins in the liver mitochondria and is completed in the liver cytosol.
Figure 02: Urea
The production of urea begins with the formation of carbamoyl phosphate. The carbamoyl phosphate enters the urea cycle or the ornithine cycle. Through a series of steps, urea is generated. The donation of the second nitrogen atom to form urea takes place with the addition of aspartate amino acid as an intermediate input.
Blood urea levels increase upon muscle injury, high catabolic rate and high protein diets. However, blood urea lowers upon liver damage or may be used up in anabolic reactions. Blood urea is a measure of a healthy individual. In blood urea nitrogen, the amount or concentration of nitrogen forming urea is specifically checked.
What are the Similarities Between Blood Urea Nitrogen and Blood Urea?
- Both provide an insight to the muscle-building rate, muscle anabolism and catabolism.
- Moreover, they also suggest muscle breakdown, decreased protein diets or malnutrition conditions.
- Dietary intake of proteins shows a key direct effect on both components.
- Both are measured in mg/dL.
- They provide an idea of nitrogen metabolism, which includes both catabolic and anabolic reactions.
- Occurrence and regulation of the urea cycle are essential for both measurements.
What is the Difference Between Blood Urea Nitrogen and Blood Urea?
Blood urea nitrogen and blood urea are very similar in their biological role and the mechanism of action. However, in blood urea nitrogen, the content of nitrogen in urea is measured while in blood urea, the total amount of urea in blood is measured. So, this is the key difference between blood urea nitrogen and blood urea.
The below infographic summarizes the difference between blood urea nitrogen and blood urea.
Summary – Blood Urea Nitrogen vs Blood Urea
The key difference between blood urea nitrogen and blood urea depends on the type of constituent measured in each parameter. In blood urea nitrogen, the nitrogen content present as urea is measured. In contrast, blood urea measures the total amount of urea present in blood upon release from the urea cycle in the liver. Both blood urea nitrogen and blood urea are indicative of the protein metabolism that takes place inside the system. Therefore, blood urea nitrogen test and blood urea test are part of the routine health screening procedures.
Reference:
1. Hosten, Adrian O. “BUN and Creatinine.” Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd Edition., U.S. National Library of Medicine, 1 Jan. 1990, Available here.
Image Courtesy:
1. “2627 Nitrogen Wastes” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Urea-3D-balls” By Jynto and Ben Mills – Derived from File:Acetamide-3D-balls.png (Public Domain) via Commons Wikimedia