What is the Difference Between BUN and Creatinine

The key difference between BUN and creatinine is that BUN (blood urea nitrogen) is a product of protein metabolism that normally gets excreted in the urine, while creatinine is a non-protein nitrogenous compound that is generated by the breakdown of creatine in muscle.

BUN and creatinine are two waste products in the human body. BUN is a waste product of protein metabolism, while creatinine is a waste product of muscle metabolism. The kidneys usually excrete these compounds via urine. Moreover, their levels in the body can be measured by specific tests, which are specifically important in certain disease diagnoses.

CONTENTS

1. Overview and Key Difference
2. What is BUN 
3. What is Creatinine
4. Similarities – BUN and Creatinine
5. BUN vs. Creatinine in Tabular Form
6. FAQ – BUN and Creatinine
7. Summary – BUN vs. Creatinine

What is BUN?

Blood urea nitrogen (BUN) is the urea concentration in the blood. The normal BUN level in the blood is less than 20 mg/dL. Amino acids are the building blocks of protein molecules. When amino acids are metabolized, nitrogen is formed into ammonia. This ammonia is toxic to the cells and converted into urea through the urea cycle so that the kidney can excrete it in the urine. Therefore, BUN is one of the significant end products of protein metabolism that is synthesized in the liver from ammonia.

A BUN test can measure blood urea nitrogen. Low levels of BUN can be due to over-hydration, low level of protein diet, or pregnancy. Moreover, higher levels of BUN can be due to kidney dysfunction, higher protein diet, dehydration, congestive heart failure, protein breakdown from the GI tract due to bleeding, trauma, and corticoid therapy. Furthermore, treatments for low  BUN levels include increasing protein intake, managing underlying liver disease, and lifestyle modifications like stopping alcohol use or losing weight, whereas treatments for high BUN levels include managing underlying causes, drinking plenty of water, and kidney dialysis.

What is Creatinine?

Creatinine is a waste product produced from the normal wear and tear of muscles of the body. Creatinine is present in the bloodstream (serum) and is filtered out of the body by the kidneys. It is produced by the breakdown of creatine in muscle. Creatine is a naturally occurring compound in the body. It is present in red meat and seafood as well. It is present in vertebrates and plays a role in the recycling of ATP within muscles and the brain. This is done by converting ADP back to ATP through the donation of phosphate groups. Moreover, creatine also acts as a buffer.

A creatinine blood test can measure creatinine. A normal result is 0.7 to 1.3 mg/dL for men and 0.6 to 1.1 mg/dL for women. Having low creatinine levels can be due to low muscle mass or body weight, chronic kidney disease, reduced kidney function, or malnutrition. High creatinine levels can be due to kidney failure, kidney obstruction, kidney infection, urinary tract obstruction, very high protein consumption, intense exercise, heart disease, and diabetes. Furthermore, low creatinine levels can be treated through medications or lifestyle changes such as eating a more healthy diet and giving up alcohol, whereas high creatinine levels can be treated through managing underlying conditions, following a healthy lifestyle, making changes to diet (low protein diet), cutting back on strenuous exercises, and avoiding creatinine supplements.

What are the Similarities Between BUN and Creatinine?

• BUN and creatinine are two waste products in the human body.
• Both are excreted by kidneys in the urine.
• The levels of both can be measured through specific blood tests.
• Their abnormal levels may indicate possible kidney disease or dysfunction.

What is the Difference Between BUN and Creatinine?

BUN is a product of protein metabolism that normally gets excreted in the urine, while creatinine is a naturally occurring non-protein compound that is a constituent of phosphocreatine, normally used to regenerate ATP within the cell.  Thus, this is the key difference between BUN and creatinine. Furthermore, BUN level is measured through a serum BUN test. On the other hand, creatine level is measured through a serum creatinine test.

The infographic below presents the differences between BUN and creatinine in tabular form for side-by-side comparison.

FAQ: BUN and Creatinine

What causes high BUN?

Heart failure, dehydration, or a diet high in protein are several reasons for high BUN.

What is the treatment of high BUN?

Eating less protein in the diet, stopping protein supplements, and drinking plenty of fluids

What is a normal BUN creatinine ratio?

The ideal ratio of BUN to creatinine falls between 10-to-1 and 20-to-1.

Summary – BUN vs. Creatinine

There are a number of waste products produced in the human body after metabolism, such as urea, creatinine, bilirubin, ammonia, carbon dioxide, etc. Therefore, BUN and creatinine are two waste products found in the human body. Both of these are nitrogenous compounds. However, BUN is a product of protein metabolism that normally gets excreted in the urine, while creatinine is a non-protein nitrogenous compound that is generated by the breakdown of creatine in muscle. So, this summarizes the difference between BUN and creatinine.

Reference:

1. “Blood Urea Nitrogen.”  Health Encyclopedia – University of Rochester Medical Center.
2. “Creatinine.” National Kidney Foundation.

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. “Creatine molecule ball” By Jynto (more from this user) – This image was created with Discovery Studio Visualizer. (CC0) via Commons Wikimedia