What Level of BUN Indicates Kidney Failure? Stages
The normal range of blood urea nitrogen (BUN) is between 7 and 20 mg/dL or 2.5 and 7.1 mmol/L. There may be slight variations between labs. A decline in kidney function can cause an increase in BUN levels. There is no definite value of BUN that would diagnose kidney failure.
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.
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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
Creatinine Test
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.
Show Sources
American Association for Clinical Chemistry: “Blood Urea Nitrogen.”
University of Rochester Medical Center: “Blood Urea Nitrogen.”
National Kidney Foundation: “Tests to Measure Kidney Function.”
Mayo Clinic: “Blood Urea Nitrogen Test” and “Heart Failure.”
Scripps Health Foundation: “BUN — Blood Test.”
U.S. National Library of Medicine: “Gastrointestinal Bleeding.”
American Association for Clinical Chemistry: “Creatinine.”
National Health Service (U.K.): “Malnutrition.”
What Level of BUN Indicates Kidney Failure? Stages
Blood urea nitrogen (BUN) is one of the parameters used to ascertain kidney function. There is no definite value of BUN that would diagnose kidney failure.
The normal range of blood urea nitrogen (BUN) is between 7 and 20 mg/dL or 2.5 and 7.1 mmol/L. There may be slight variations between labs. A decline in kidney function can cause an increase in BUN levels. There is no definite value of BUN that would diagnose kidney failure.
BUN and creatinine tests can be used together to find the BUN-to-creatinine ratio (BUN:creatinine), which is more specific than the BUN test alone. More specific tests such as glomerular filtration rate (GFR) and creatinine clearance may be performed further to diagnose kidney failure. A high BUN value may be due to reasons unrelated to the kidneys such as:
- High protein diet
- Burns
- Dehydration
- Hemorrhage
- Shock
- Heart diseases such as congestive heart failure or a recent heart attack
- Certain medicines
- Older age
If your BUN values are consistently outside the normal limits, talk to your doctor to know the reason behind the variation.
What are kidneys and kidney function tests?
Kidneys are vital organs performing various functions such as maintaining fluid and electrolyte balance, controlling blood pressure, removing waste products from the body, maintaining healthy bones (by activating vitamin D) and keeping healthy levels of red blood cells (RBCs) in the body. Various tests are performed to know about the health of the kidneys such as:
- Blood urea
- Serum creatinine
- Blood urea nitrogen (BUN)
- Glomerular filtration rate (GFR)/eGFR
- Creatinine clearance
- Urine proteins
- Urine microalbumin
- Serum electrolytes
- Complete blood counts (CBC)
QUESTION
What is BUN?
Blood urea nitrogen (BUN) is one of the parameters measured to ascertain kidney function. A BUN test is also known by other names such as a urea nitrogen test and serum BUN. BUN indicates the urea nitrogen produced in the body during protein breakdown. It is removed from the body through urine.
A decline in kidney function due to a disease or kidney damage can cause an increase in BUN. It is, however, a less specific indicator of compromised kidney function than glomerular filtration rate (GFR) and creatinine clearance. This is because BUN values can vary independent of kidney function.
Your BUN values may be low if you eat a low protein diet, whereas they may increase with a high-protein diet. BUN can also increase in case of internal bleeding (hemorrhage), injuries and glucocorticoid therapy. Liver diseases can also cause a lower BUN value.
Why is a BUN test done?
A blood urea nitrogen (BUN) test may be performed as part of your routine checkup. Your doctor may also advise a BUN test if you have any factors that may increase the risk of kidney diseases. The risk factors include:
- Family history of kidney problems
- High blood pressure
- Diabetes
- Kidney diseases
- Long-term medications
The doctor may also advise the BUN test if you have any signs and symptoms of kidney diseases such as:
- Swelling of the feet, legs or arms
- Increased or decreased urine frequency
- Having trouble sleeping
- Dry and itchy skin
- Abnormal appearance of urine (foamy or blood-tinged urine)
- Muscle cramps
- Excessive fatigue
- Reduced appetite
What happens during a BUN test?
A blood urea nitrogen (BUN) test is a quick and simple test that generally takes less than 5 minutes. You do not need to prepare for it. During the test, a healthcare professional takes a blood sample from a vein in your arm using a small needle. They will withdraw a small amount of blood and collect it in a special test vial. You may feel a little sting when the needle is inserted or withdrawn. You may get the results of the test within 24 to 48 hours depending upon the sample load of the lab.
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What are signs and symptoms of kidney failure?
Symptoms of kidney failure typically begin in the later stages, and there may be very few symptoms in the early stages.
Early symptoms kidney failure may include:
- Decreased urine output
- Shortness of breath
- Disorientation
- Fluid retention (swelling in the limbs)
Other possible symptoms of kidney failure may include:
- Anemia
- Bad breath
- Bone pain
- Changes to skin color or pale skin
- Changes in urine appearance or blood in the urine
- Confusion or memory problems
- Easy bruising
- Fatigue
- Headaches
- High blood pressure that is resistant to medications
- Itchy, dry skin
- Lack of concentration
- Loss of appetite
- Metallic taste in the mouth
- Muscle twitches, cramps, or weakness
- Nausea and vomiting
- Numbness and tingling in fingers or toes
- Seizures
- Trouble sleeping
- Weak bones with increased susceptibility to fractures
- Weight loss
What is the first stage of kidney failure?
Kidney failure symptoms can be difficult to detect in early stages. Learn about the 5 stages of kidney failure
Kidney failure, also called renal failure or end-stage kidney disease, occurs when at least 85% of kidney function has been lost.
When your kidneys fail, it causes waste products to build up in the body, which can lead to chemical imbalances in the blood and be fatal if left untreated. People with chronic kidney failure may develop low blood counts or weak bones over time, requiring dialysis or a kidney transplant.
Kidney failure can happen suddenly or gradually. But many people don’t experience any symptoms until their kidneys are already close to complete failure.
SLIDESHOW
Understanding the 5 stages of kidney failure
The five stages of kidney failure range from very mild damage (stage I) to complete kidney failure (stage V). Stages are based on declining kidney function and glomerular filtration rate (GFR) measurements, which is the rate at which kidneys filter waste from the body.
GFR is calculated based on a blood test that estimates the amount of creatinine (waste product) in the blood. A higher GFR indicates a healthy kidney, whereas lower GFR indicates a suboptimal kidney function. A normal GFR is about 90 to 120 mL/min/1.73 m2.
Symptoms and complications increase as the stages progress.
Stage I (normal or minimal loss of kidney function)
Kidney damage is very mild with GFR 90 mL/min/1.73 m2 or above (normal values). No symptoms are present, but there might be indications of kidney damage in tests, such as the presence of protein in the urine or physical changes of kidneys on a sonogram.
Stage II (mild or moderately reduced kidney function)
Mild kidney damage with GFR between 60 and 89 mL/min/1.73 m2. The filtration rate is slightly subpar. No symptoms are present, but certain indications may be more obvious, such as protein in the urine or physical damage to the kidneys.
Stage III (moderate to severe loss of kidney function)
Kidneys do not work as efficiently as they should, and GFR is between 30 and 59 mL/min/1.73 m2. Symptoms may become apparent at this stage and may include fatigue, swelling in hands and feet, back pain, frequent or infrequent urination, and high blood pressure.
Stage III kidney disease is divided into IIIA and IIIB.
- Stage IIIA (early) refers to GFR between 45 and 59 mL/min/1.73 m2.
- Stage IIIB (late) refers to GFR between 30 and 44 mL/min/1.73 m2.
Stage IV (severely reduced kidney function)
Kidneys are severely damaged with GFR between 15 and 29 mL/min/1.73 m2. This is the last stage before complete kidney failure. Symptoms such as fatigue, swelling, and back pain, may worsen and cause health complications such as anemia, high blood pressure, and bone disease.
Stage V (kidney failure or end-stage renal disease or ESRD)
Kidneys are close to or in complete failure with GFR less than 15 mL/min/1.73 m2. Symptoms of kidney failure become evident and include loss of appetite, vomiting and nausea, muscle cramps, swelling in hands and feet, back pain, urinating more or less than normal, trouble sleeping, breathing trouble, and itchy skin. Patients with kidney failure will need dialysis or a kidney transplant to survive.
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Medically Reviewed on 3/4/2022
References
Medscape Medical Reference
National Kidney Foundation
American Kidney Fund. Kidney Failure (ESRD) Causes, Symptoms, & Treatments. https://www.kidneyfund.org/kidney-disease/kidney-failure/
Workeneh BT. Acute Kidney Injury. Medscape. https://emedicine.medscape.com/article/243492-overview
Arora P. Chronic Kidney Disease (CKD). Medscape. https://emedicine.medscape.com/article/238798-overview
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