What is the Difference Between BUN and Urea

The main difference between BUN and urea is that BUN (Blood Urea Nitrogen) is only the nitrogen content of urea, whereas urea measures the whole urea molecule.

In short, BUN and urea are two measurements important to assess the renal function. Generally, kidney disease reduces the excretion of urea from the body, allowing the accumulation of urea in the blood. Urea is the principal nitrogenous waste product in humans. Moreover, the body exclusively eliminates urea by the kidney.

Key Areas Covered

1. What is BUN (Blood Urea Nitrogen)
   • Definition, Features
2. What is Urea
   • Definition, Features
3. Similarities Between BUN and Urea
   • Outline of Common Features
4. Difference Between BUN and Urea
   • Comparison with Key Differences

Key Terms

BUN, Renal Function, Urea

What is BUN (Blood Urea Nitrogen)

BUN or blood urea nitrogen is a medical test that measures the amount of urea nitrogen in the blood. The liver produces urea in the urea cycle as a waste product of protein breakdown. Normally, human blood can contain 6 To 20 mg/dL (2.1 to 7.1 mmol/L) of urea nitrogen. The BUN measurement reflects renal health.

Figure 1: Urea

A high protein diet, decrease in glomerular filtration rate (GFR), decrease in blood volume (hypovolemia), congestive heart failure, gastrointestinal hemorrhage, fever, rapid cell destruction from infections, athletic activity, excessive muscle breakdown, and increased catabolism are the reasons behind increase BUN.

What is Urea

Urea is the principal nitrogenous waste in the human body produced as a result of metabolism. The kidney is the organ responsible for the exclusive removal of urea from the body. Moreover, urea is a simple organic molecule (MW 60) and comprises two amino groups and one carbonyl group. Proteins are first degraded into amino acids. Then, these amino acids gradually break down to ammonia, which is toxic. In the meanwhile, the urea cycle converts ammonia into non-toxic urea.

Figure 2: Urea Cycle

Moreover, a high-protein diet results in the production of high urea content while a low-protein diet results in the production of low urea content. On the other hand, a small amount of urea (<10%) is eliminated through sweat and the gut. But, the rest of the urea content travels through the bloodstream from the liver to the kidney. That means urea passes from the bloodstream to the glomerular filtrate inside the kidney.   

Similarities Between BUN and Urea

• BUN and urea are two types of measurements of urea in the body.
• Non-removal of urea through the urine can indicate different health conditions.
• In addition, a high-protein diet results in a higher amount of urea in the blood.

Difference Between BUN and Urea

Definition

BUN or blood urea nitrogen refers to a medical test that measures the amount of urea nitrogen in the blood while urea refers to the medical test that measures the amount of urea in the blood.

Measures

The BUN test measures the amount of nitrogen in blood while the urea test measures the amount of blood urea.

Reference Value

Moreover, the serum BUN level is 7.0-22 mg/dL while the serum urea level is 2.5-7.8 mmol/L.

Molecular weight

The molecular weight of BUN is 28 while the molecular weight of urea is 60.

Involvement of Kidney

BUN reflects kidney function while urea reflects protein metabolism.

Conclusion

In brief, Bun or blood urea nitrogen is a medical test that measures the amount of urea nitrogen in the blood. Its reference level is 7-22 mg/dL. This test also reflects the protein diet of a person. Moreover, in a high-protein diet, BUN increases. On the other hand, urea is the other medical test that measures the urea content in the blood. Its reference value is 2.5-7.8 mmol/L. Therefore, the main difference between BUN and urea is their relevant measurements.

References:

1. Urea and the clinical value of measuring blood urea concentration. Retrieved August 10, 2022.
2. Wikimedia Foundation. (2022, April 15). Blood urea nitrogen. Wikipedia. Retrieved August 10, 2022.   

Image Courtesy:

1. “Urea-3D-balls” By Jynto and Ben Mills – Own Work (Public Domain) via Commons Wikimedia
2. “Urea Cycle” By Zachary P. Christensen (CC BY-SA 4.0) via Commons Wikimedia