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High levels can also indicate the following:
What Is a Blood Urea Nitrogen Test?
Your doctor may order a blood urea nitrogen test as part of a routine health screening. It helps them see how well your kidneys are working.
Urea nitrogen is a normal waste product that your body creates after you eat. Your liver breaks down the proteins in your food — and while it does that, it creates blood urea nitrogen, also known as BUN. Your liver releases the substance into the blood, and it eventually ends up in your kidneys.
When your kidneys are healthy, they remove the BUN, usually leaving a small amount of it in the blood. But for the most part, your kidneys get rid of it by flushing it out of your body through urine.
When your kidneys are not healthy, they have trouble removing BUN and leave more of it in your blood.
The blood urea nitrogen test, which is also called a BUN or serum BUN test, measures how much of the waste product you have in your blood. If your levels are off the normal range, this could mean that either your kidneys or your liver may not be working properly.
Why You Get the BUN Test
Your doctor may order a BUN test as part of a routine checkup. It may be one of several blood tests that you get.
If you have a kidney condition, the test is a way to check what your BUN levels are before you start a medication or treatment. Also, it’s standard for a BUN test to be given when you’re in the hospital for certain conditions.
If your doctor suspects you may be getting kidney problems, they may order the BUN test.
Tell your doctor if you have the following symptoms, which can be signs that something is wrong with your kidneys:
● A change in how much you urinate
● Pee that is foamy, bloody, discolored, or brown
● Swelling in your arms, hands, legs, ankles, around your eyes, face, or abdomen
● Pain in the mid-back where kidneys are located
● You’re tired all the time
How Do I Prepare for the Test?
Before the blood test, tell your doctor what medications you’re taking. If any of them might alter the test result, your doctor may ask you to stop taking them for a period of time.
If you’re only getting a BUN test, you can eat and drink. But if you’re getting other blood tests, your doctor may give you directions that may include fasting before the test.
What Happens During the Test?
A lab tech will take a sample of your blood from a vein in your arm or the back of your hand. You may feel a slight sting when the needle pricks through your skin.
It may feel a little bit sore afterward, but you can go straight back to your everyday activities.
Your doctor’s office will send the blood sample to a lab to be analyzed. You should get the results in a few days, depending on how fast the lab and your doctor’s office can work.
Understanding Your Results
Your result will be a number that measures how much BUN is in your blood. The range considered normal is between 7 to 20 milligrams per deciliter. (A milligram is a very tiny amount — more than 28,000 to an ounce, and a deciliter is equal to about 3.4 ounces).
If your test results are not in that range, talk to your doctor.
Several things can affect your BUN test results, so having a BUN level that is lower or higher than the normal range doesn’t always mean there is a problem.
Things that affect your BUN level might include:
● High-protein diet (may cause high BUN levels)
● Low-protein diet (may cause low BUN levels)
● Several medications, including steroids and antibiotics (increased or decreased BUN levels)
What High BUN Levels Can Mean
High BUN levels can also indicate various problems with your kidneys. Talk to your doctor about what could be causing the problem and plan your next steps.
High levels can also indicate the following:
● Urinary tract obstruction (blockage from being able to pee)
● Congestive heart failure (when your heart doesn’t pump blood to your body like it should)
Low BUN levels are rare. If you have low BUN levels, it could indicate:
● Malnutrition (when your diet doesn’t have enough nutrients or your body can’t take them in well)
● Overhydration (having too much fluid)
But a BUN test is not a way to diagnose these issues, so more tests may be needed
Your doctor may also order a creatinine test, which is another blood test that also checks your kidney health. This is because the BUN level by itself doesn’t always reveal much.
When your BUN levels are compared with your creatinine levels, it gives a fuller picture of what’s happening with your kidneys. This is known as the BUN/Creatinine ratio.
Creatinine is a waste product from your muscles that is also filtered by your kidneys. Like BUN, high levels of creatinine could mean there is a lot of waste product that hasn’t been removed by the kidneys.
The ideal ratio of BUN to creatinine falls between 10-to-1 and 20-to-1.
Having a ratio above this range could mean you may not be getting enough blood flow to your kidneys, and could have conditions such as congestive heart failure, dehydration, or gastrointestinal bleeding.
A ratio below the normal range could mean liver disease or malnutrition.
BUN/Creatinine Ratio: High & Low Levels + Normal Range
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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 .
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 .
Low BUN/Creatinine Ratio
- Low protein intake, seen in conditions of malnutrition and starvation. Less protein means lower BUN production .
- Advanced liver disease, when the liver can’t produce enough urea, resulting in lower BUN levels .
- Sickle cell anemia – in this condition kidneys reabsorb less urea and more of it is lost in the urine, resulting in lower BUN .
- 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 .
- Kidney damage and kidney failure. When kidneys become impaired for any reason, creatinine blood levels will rise .
- Drugs such as acetazolamide, a diuretic used to treat various conditions including glaucoma, epilepsy, altitude sickness, and heart failure .
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 .
- 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 .
- 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 .
- 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 .
- Reducing alcohol consumption. Alcohol blocks the production of urea (BUN) .
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 .
- Losing some weight if overweight. Weight loss can improve your kidney health and decrease creatinine levels .
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
Joe Cohen, BS
Joe Cohen flipped the script on conventional and alternative medicine…and it worked. Growing up, he suffered from inflammation, brain fog, fatigue, digestive problems, insomnia, anxiety, and other issues that were poorly understood in traditional healthcare. Frustrated by the lack of good information and tools, Joe decided to embark on a learning journey to decode his DNA and track his biomarkers in search of better health. Through this personalized approach, he discovered his genetic weaknesses and was able to optimize his health 10X better than he ever thought was possible. Based on his own health success, he went on to found SelfDecode, the world’s first direct-to-consumer DNA analyzer & precision health tool that utilizes AI-driven polygenic risk scoring to produce accurate insights and health recommendations. Today, SelfDecode has helped over 100,000 people understand how to get healthier using their DNA and labs.
Joe is a thriving entrepreneur, with a mission to empower people to take advantage of the precision health revolution and uncover insights from their DNA and biomarkers so that we can all feel great all of the time.
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