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BUN/Creatinine Ratio: High & Low Levels + Normal Range

Written by Puya Yazdi, MD | Last updated:
Jonathan Ritter
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology) | Written by Puya Yazdi, MD | Last updated:

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Kidneys

BUN (blood urea nitrogen) and creatinine are two blood tests that can reveal a lot about your metabolism, kidney, liver, and overall health. And while they can be used separately, the BUN/creatinine ratio can help pinpoint important issues. Learn more about the BUN/creatinine ratio and what it can reveal about your health.

What is the BUN/Creatinine Ratio?

BUN (blood urea nitrogen) and creatinine are two lab tests that are often ordered as part of a comprehensive metabolic panel. Your doctor may order this panel to get an idea of your overall health and metabolism.

BUN measures the amount of urea in your blood. Urea is a waste product made in the liver as the body processes protein. This protein is mostly derived from the diet, but it can also result from tissue protein turnover [1, 2, 3].

Urea is removed by the kidneys, but the rate of removal depends on the needs of the body. The kidneys can return different amounts of urea into the bloodstream depending on factors such as hydration and blood pressure. High urea is an important marker of kidney dysfunction as well [1, 2, 3].

Creatinine, on the other hand, is a waste product created from the normal wear and tear of muscles. It is produced from creatine, a protein that helps generate energy for muscle contractions. Creatinine production essentially reflects muscle mass, and because this mass changes little from day to day, creatinine production tends to be fairly constant [3, 4, 5].

Creatinine is removed from the body by the kidneys, which filter almost all of it from the blood into the urine, at a fairly constant rate. That is why blood levels are usually a good indicator of how well your kidneys are working [3, 4, 5].

So to recap, BUN levels fluctuate, while creatinine is removed at a constant rate and its blood levels are usually stable. That’s why the BUN/Creatinine ratio can be used to check for issues such as dehydration, kidney injury/disease, gut bleeding, and other problems [3].

BUN/Creatinine Ratio Normal Range

The normal range for BUN/Creatinine ratio is anywhere between 5 – 20 mg/dL.

BUN/Creatinine ratio increases with age, and with decreasing muscle mass [6].

Low BUN/Creatinine Ratio

A low BUN/Creatinine ratio indicates an underlying disease/disorder and will usually be accompanied by the symptoms of this underlying disorder. The causes shown here are commonly associated with low BUN/creatinine. Work with your doctor or other health care professional for an accurate diagnosis.

A BUN/Creatinine ratio lower than normal can be caused by:

  • Low protein intake, seen in conditions of malnutrition and starvation. Less protein means lower BUN production [3].
  • Advanced liver disease, when the liver can’t produce enough urea, resulting in lower BUN levels [3].
  • Sickle cell anemia – in this condition kidneys reabsorb less urea and more of it is lost in the urine, resulting in lower BUN [3].
  • Hypothyroidism, a condition where the thyroid glands do not produce enough thyroid hormone. This condition can increase creatinine levels [7, 8].
  • Rhabdomyolysis, a condition in which damaged muscles breaks down rapidly, resulting in higher creatinine levels [3].
  • Kidney damage and kidney failure. When kidneys become impaired for any reason, creatinine blood levels will rise [9].
  • Drugs such as acetazolamide, a diuretic used to treat various conditions including glaucoma, epilepsy, altitude sickness, and heart failure [10].

High BUN/Creatinine Ratio

A high BUN/Creatinine ratio indicates an underlying disease/disorder and will usually be accompanied by the symptoms of this underlying disorder. The causes shown here are commonly associated with high BUN/creatinine. Work with your doctor or other health care professional for an accurate diagnosis.

A BUN/Creatinine ratio above the normal range can be caused by:

  • Dehydration. Dehydration increases the blood levels of both BUN and creatinine but increases BUN more than creatinine [11].
  • Gut bleeding. The blood in the gut gets digested and this increases the amount of protein and BUN levels [12, 13].
  • Hyperthyroidism. This condition can increase BUN and lower creatinine levels [7].
  • Congestive heart failure – heart failure increases the reabsorption of urea and increases blood BUN levels [14, 15].
  • Kidney disease, it can increase BUN as well as creatinine levels [16].
  • Drugs such as tetracycline (an antibiotic) or corticosteroids (used to treat inflammation) [10, 3, 17].

Factors that Increase BUN/Creatinine Ratio

It is important to address any health condition that may be causing the disbalance. Once the condition has been resolved, the BUN/creatinine ratio should return to a normal range. Your doctor will work to find an accurate diagnosis and an appropriate treatment plan, which may include some of the strategies below. Never use any of these in place of what your doctor prescribes.

Factors that Increase BUN

  • Increasing dietary protein. Low BUN levels may mean that you are not consuming enough protein. If this is the case, try to increase your consumption of high-protein foods like lean meats and beans [1].
  • Reducing alcohol consumption. Alcohol blocks the production of urea (BUN) [18].

Factors that Decrease Creatinine

  • Avoiding creatine and creatine-based supplements
  • Increasing dietary fiber. Vegetable and fruit fiber improves kidney health and can lower blood creatinine levels [19].
  • Losing some weight if overweight. Weight loss can improve your kidney health and decrease creatinine levels [20].

How to Decrease Your BUN/Creatinine Ratio

Again, disbalance between BUN and creatinine is often due to a serious medical condition and it is important to address it. Once the condition gets resolved, the BUN/creatinine ratio will go back into the normal range. Your doctor will work to find an accurate diagnosis and an appropriate treatment plan, which may include some of the strategies below. Never use any of these in place of what your doctor prescribes.

Factors that Decrease Bun

  • Drinking more water. Make sure you are properly hydrated.
  • Losing weight if overweight. A high BMI can cause kidney dysfunction and increase BUN (urea) levels [21, 22, 23].

Factors that Increase Creatinine

  • Increasing physical activity (unless it’s not recommended due to an existing medical condition) – exercise increases creatinine levels + it helps build muscle [24, 25].
  • Avoid alcohol. It may decrease blood creatinine [26, 27].

About the Author

Puya Yazdi

Puya Yazdi

MD
Dr. Puya Yazdi is a physician-scientist with 14+ years of experience in clinical medicine, life sciences, biotechnology, and nutraceuticals.
As a physician-scientist with expertise in genomics, biotechnology, and nutraceuticals, he has made it his mission to bring precision medicine to the bedside and help transform healthcare in the 21st century.He received his undergraduate education at the University of California at Irvine, a Medical Doctorate from the University of Southern California, and was a Resident Physician at Stanford University. He then proceeded to serve as a Clinical Fellow of The California Institute of Regenerative Medicine at The University of California at Irvine, where he conducted research of stem cells, epigenetics, and genomics. He was also a Medical Director for Cyvex Nutrition before serving as president of Systomic Health, a biotechnology consulting agency, where he served as an expert on genomics and other high-throughput technologies. His previous clients include Allergan, Caladrius Biosciences, and Omega Protein. He has a history of peer-reviewed publications, intellectual property discoveries (patents, etc.), clinical trial design, and a thorough knowledge of the regulatory landscape in biotechnology.He is leading our entire scientific and medical team in order to ensure accuracy and scientific validity of our content and products.

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