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 are often used separately, calculating the BUN/creatinine ratio can further 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 measured as a 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 – kidneys can return different amounts of urea into the blood stream depending on factors such as hydration and blood pressure [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, the production rate is also 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, while BUN levels fluctuate because kidneys can return urea into the blood stream depending on body’s needs, creatinine gets removed at a constant rate and its blood levels are usually stable [3]. That’s why the BUN/Creatinine ratio can be used to check for issues such as dehydration, kidney injury/disease, gut bleeding, etc…

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

Low BUN/Creatinine ratio will not cause symptoms on its own. However, people will often experience symptoms of the underlying disease/disorder.

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

High BUN/Creatinine ratio will not cause symptoms. Nevertheless, people will often experience symptoms of the underlying disease/disorder.

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 conditions can both 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].

How to Increase Your BUN/Creatinine Ratio

It is important to address any health condition that may be causing the disbalance. Once the condition improves, the BUN/creatinine ratio will return to a normal range.

You can further help increase your BUN/Creatinine ratio by either increasing your BUN (if it’s on the low side) or decreasing your creatinine (if it’s high).

Increase low BUN by:

  • 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].

Decrease high creatinine by:

  • 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, BUN/creatinine ratio will go back into the normal range.

You can help decrease the BUN/Creatinine ratio by lowering BUN (if it’s high) or increasing creatinine (if it’s low).

Decrease BUN by:

  • 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].

Increase creatinine by:

  • 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].

Irregular BUN/Creatinine Ratio?

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