- Urea and the clinical value of measuring blood urea concentration
- Measurement of plasma/serum urea – a note on nomenclature and units
- Causes of increased serum/plasma urea
- Non-renal causes of increased plasma/serum urea
- Causes of reduced plasma/serum urea
- Urea Test: High & Low Levels + Normal Range
- What is Urea?
- Urea Test
- Urea Normal Range
- Low Urea Levels
- Factors that Increase Urea Levels
- High Urea Levels
- Causes of High Urea
- Factors that Decrease Urea Levels
- Blood Urea Nitrogen (BUN) – Understand the Test
- Understanding Your Lab Values
- BUN levels: Measurements, results, and procedure
- Symptoms of liver and kidney disease
Urea and the clinical value of measuring blood urea concentration
This process of renal elimination, which is detailed in a recent review , begins with filtration of blood at the glomeruli of the approximately 1 million nephrons contained within each kidney.
During glomerular filtration, urea passes from blood to the glomerular filtrate, the fluid that is the precursor of urine. The concentration of urea in the filtrate as it is formed is similar to that in plasma so the amount of urea entering the proximal tube of the nephron from the glomerulus is determined by the glomerular filtration rate (GFR).
Urea is both reabsorbed and secreted (recycled back into the filtrate) during passage of the filtrate through the rest of the tubule of the nephron; the net effect of these two processes results in around 30-50 % of the filtered urea appearing in urine.
The facility of the kidney to adjust urea reabsorption and secretion as the filtrate passes through the tubule determines an important role for urea in the production of a maximally concentrated urine, when this becomes necessary.
The mechanism of this water-conserving action of urea within the nephron is well detailed by Weiner et al .
Although often considered simply a metabolic waste product, urea has two important physiological functions outlined above: detoxification of ammonia and water conservation.
Measurement of plasma/serum urea – a note on nomenclature and units
Around the world, essentially the same method of urea analyses is used, but the result is expressed in two quite different ways . In the US and a few other countries, plasma or serum urea concentration is expressed as the amount of urea nitrogen.
Although plasma or serum is used for the analysis, the test is still, somewhat confusingly, commonly referred to as blood urea nitrogen (BUN), and the unit of BUN concentration is mg/dL.
In all other parts of the world, urea is expressed as the whole molecule (not just the nitrogen part of the molecule) in SI units (mmol/L). Since BUN reflects only the nitrogen content of urea (MW 28) and urea measurement reflects the whole of the molecule (MW 60), urea is approximately twice (60/28 = 2.14) that of BUN.
Thus BUN 10 mg/dL is equivalent to urea 21.4 mg/dL.
To convert BUN (mg/dL) to urea (mmol/L):
multiply by 10 to convert from /dL to /L and divide by 28 to convert from mg BUN to mmol urea, i.e. 10/28 = 0.357
So the conversion factor is 0.357BUN mg/dL multiplied by 0.357 = urea (mmol/L)
Urea (mmol/L) divided by 0.357 = BUN (mg/dL)
Approximate reference (normal) range:Serum/plasma urea 2.5-7.8 mmol/L
Serum/plasma BUN 7.0-22 mg/dL
[It is widely accepted that there is an age-related increase in plasma/serum urea concentration , but this is not well defined and there is uncertainty as to whether it simply reflects an age-related decline in renal function as some studies  suggest, or occurs despite normal renal function as others  seem to suggest. The results of  suggest that healthy elderly individuals (without any apparent loss of renal function), may have BUN levels as high as 40-50 mg/dL
Causes of increased serum/plasma urea
Serum/plasma urea concentration reflects the balance between urea production in the liver and urea elimination by the kidneys, in urine; so increased plasma/serum urea can be caused by increased urea production, decreased urea elimination, or a combination of the two.
By far the highest levels occur in the context of reduced urinary elimination of urea due to advanced renal disease and associated marked reduction in glomerular filtration rate (GFR).
GFR is a parameter of prime clinical significance because it defines kidney function. All those with reduced kidney function, whatever its cause have reduced GFR and there is good correlation between GFR and severity of kidney disease.
The rate of decline in GFR distinguishes chronic kidney disease (CKD) and acute kidney injury (AKI). CKD is associated with irreversible slow decline in GFR over a period of many months, years or even decades; whereas AKI is associated with precipitous decline in GFR over a period of hours or days; AKI is potentially reversible.
The value of urea as a test of renal function depends on the observation that serum/plasma urea concentration reflects GFR: as GFR declines, plasma/serum urea rises.
The limitation of urea as a test of renal function is that in some circumstances plasma urea is not a sufficiently accurate reflection of GFR. For example, urea is an insensitive indicator of reduced GFR; GFR must be reduced by around 50 % before serum/plasma urea increases above the upper limit of the reference range .
Furthermore, urea may be raised despite a normal GFR (i.e. normal renal function) so as a test of renal function, urea lacks specificity ,,.
Non-renal causes of increased plasma/serum urea
The causes of increased plasma/serum urea in association with normal GFR, i.e. normal renal function, include the physiological and the pathological. The two physiological causes are increased dietary protein and ageing.
As previously mentioned, increase in dietary protein results in increased urea production. If sufficiently marked, this increased urea production can cause plasma/serum urea to rise. Mention has also been made of the age-related increase in plasma/ serum urea.
Gastrointestinal hemorrhage is associated with increased protein intake (blood in the gut is effectively a high-protein meal) and thereby increased urea production and consequent increased plasma/serum urea .
Increased protein catabolism and consequent increased urea synthesis accounts, at least in part, for the increased plasma/serum urea that accompanies conditions that are associated with tissue damage, e.g. trauma, major surgery, starvation, severe infection.
The role of urea in the maximal conservation of water by the kidney involves increased urea reabsorption and consequent tendency to mild increase in plasma/serum urea.
Low circulatory states such as heart failure , dehydration , hypovolemic shock, necessarily invoke aspects of this adaptive response and all may be associated with mild increase in plasma/serum urea, despite normal GFR.
Drugs that induce a catabolic state with increased protein breakdown and consequent increased urea production can cause plasma/serum urea to rise slightly; the most widely cited drug group to have this effect is the corticosteroids.
Causes of reduced plasma/serum urea
Reduced plasma/serum urea is less common  and usually of less clinical significance than increased plasma/serum urea.
Since urea concentration in plasma or serum reflects the balance between urea production and urea elimination in urine, reduced plasma/serum urea can be caused by decreased urea production, increased urinary urea excretion, or a combination of the two.
There are two physiological causes of reduced concentration: low-protein diet, and pregnancy.
Low-protein diet is associated with reduced urea production and consequent tendency to reduced plasma/serum urea concentration.
The reduced plasma/serum urea that commonly occurs during pregnancy is due to the combined effect of reduced urea production and increased urea excretion . The increased urea excretion is consequent on increased GFR, a welldocumented physiological adaptation to pregnancy.
Pathological cause of reduced urea concentration is largely confined to advanced liver disease .
This reflects the central role that the liver plays in urea production via the urea cycle. Inherited deficiency of any one of the five enzymes of the urea cycle describes a rare group of conditions (called the urea cycle defects) that can give rise to reduced urea synthesis and consequent reduced plasma/serum urea concentration.
A recently published case history  exemplifies this very rare cause of decreased plasma/serum urea. Overhydration induces increased GFR and consequent increased excretion of urea. For this reason overhydration, as might occur, for example, in the syndrome of inappropriate antidiuretic hormone (SIADH), is often associated with decreased plasma/serum urea.
The causes of increased and decreased plasma/serum urea are listed in boxes below:
|Causes of increased plasma/serum urea concentration (i.e. urea >7.8 mmol/L or BUN >22 mg/dL)|
In general, the non-renal causes of increased plasma/serum urea result in a mild to moderate increase (usually no greater than 10.0 mmol/L (BUN 28 mg/dL). Concentration in patients with renal dysfunction can range from mildly increased to severely increased, depending on severity of disease.
Those with end-stage renal failure, requiring renal replacement therapy (dialysis, renal transplantation) may have plasma/serum urea >50.0 mmol/L (BUN >140 mg/dL).
The higher the concentration above 10 mmol/L, the greater is the chance that it is due to renal disease, but a slight increase cannot, of itself, be assumed to be due to a non-renal cause.
|Causes of decreased plasma/serum urea concentration (i.e. urea|
Urea is a waste product of metabolism that is excreted by the kidneys in urine. Kidney disease is associated with reduced urea excretion and consequent rise in blood concentration.
Once the primary laboratory test for detection and monitoring of reduced renal function (kidney disease), that role is now fulfilled by the plasma/serum creatinine test.
The limitation of urea as a test of renal function relates to reduced sensitivity and specificity so that a normal urea does not necessarily exclude renal disease and a slight to moderate increase in urea cannot be assumed to be due to renal disease.
There are many non-renal causes that can be associated with such a rise and for some of these conditions, e.g. heart failure, dehydration is common. By comparison with urea, creatinine measurement is no more sensitive but is more specific.
Under some circumstances urea may be more sensitive for detection of early renal disease than creatinine, so it has some advantage.
These issues will be explored further in a second article that will focus on the clinical value of measuring urea and creatinine together and calculating the urea: creatinine ratio.
Urea Test: High & Low Levels + Normal Range
Urea is an important measure of kidney health, liver health, and protein turnover. A urea blood test is often ordered as a part of a comprehensive metabolic panel, which gives a broad overview of a person’s metabolic and overall health. How do doctors use this test? Read on to find out.
What is Urea?
Urea is a waste product that the liver makes when it degrades proteins, both from the diet and from tissue protein turnover [1, 2, 3].
On a normal/average diet, we produce about 12 g of urea each day . The bulk of it, about 10 g each day, is eliminated by the kidneys .
A small amount of urea (less than 0.5 g/day) leaves the body through the gut, lungs, and skin. During exercise, a substantial amount may be lost through sweat .
Blood urea levels represent the balance between urea production (in the liver), urea breakdown, and urea elimination by the kidneys .
Therefore, urea can be a useful indicator of kidney health and liver health. It is also used to check for severe dehydration.
Doctors often order the urea test for people who are experiencing signs and symptoms of kidney dysfunction. These symptoms can include:
- Frequent urination
- Discolored urine (bloody, dark, or foamy)
- Joint pain
- Bone pain
- Back pain
- Muscle cramping
- Restless legs
- Trouble sleeping
- Poor appetite
- Swelling (especially in the extremities)
Urea Normal Range
In Europe, the whole urea molecule is measured. Normal human blood should contain between 1.8 – 7.1 mmol/L .
In the United States only the nitrogen component of urea is measured (the blood urea nitrogen, i.e., BUN), which is roughly one-half of blood urea. The normal range for BUN is between 5 – 20 mg/dL .
To convert from mmol/L into mg/dL, divide by 0.357.
The range is wide because there are many factors that affect blood urea levels :
- the amount of protein in the diet
- protein breakdown
- state of hydration
- liver urea production
- urea elimination by the kidneys
Urea can both decrease and/or increase in pregnancy [5, 6].
Low Urea Levels
Low urea levels are often not of great concern. However, in some cases, they point to underlying issues:
- Low-protein diet, malnutrition, or starvation 
- Impaired liver activity due to liver disease, often linked to alcohol abuse [3, 7]
- Overuse of anabolic steroids, which decrease protein breakdown 
- Overhydration, or drinking too much water 
- Growth hormone use. Growth hormone-deficient children given human growth hormone have lower urea, and this is due to decreased urea production [9, 10]
- Genetic deficiency of urea cycle enzymes 
If low urea levels are combined with worrying symptoms or other abnormal lab markers, your doctor will consider all of these factors to make an accurate diagnosis.
Urea can also be decreased in pregnancy, but it is not used to determine whether someone is pregnant because urea levels tend to be highly variable during this time .
Factors that Increase Urea Levels
Low urea levels may indicate an underlying health problem that requires medical attention. Rather than trying to artificially increase urea, work with your doctor to diagnose and treat any condition that may be causing low urea. You may also try the following strategy if your doctor determines that it is appropriate.
Low urea levels may mean that you are not consuming enough protein. If this is the case, you may need to increase your consumption of protein-rich foods lean meats or beans .
High Urea Levels
High urea levels can result from serious underlying health conditions and diseases. In addition, elevated urea may increase oxidative stress in cells [11, 12].
High urea indicates increased protein breakdown, which is associated with decreased immune function. In a study of 26,000 critically ill patients, those with elevated urea were more ly to suffer infections and to die while hospitalized .
High urea was also associated with increased mortality in ill patients in three other studies of several hundred patients each [4, 13, 14, 15].
Elevated urea has also been associated with increased stroke risk in heart surgery (5498 subjects), and adverse outcomes in atherosclerosis (1521 subjects) and heart failure patients (225 patients) [16, 17, 18].
Blood urea levels tend to increase as we age .
Levels can also rise in pregnancy, but they are not used to determine whether someone is pregnant because urea levels are highly variable during this time .
Causes of High Urea
Causes shown here are commonly associated with high urea. Work with your doctor or other health care professional for an accurate diagnosis.
- Kidney disease or failure, and blockage of the urinary tract by a kidney stone 
- Dehydration/low water consumption – Urea increases as blood volume decreases 
- High protein diets 
- Fever or infection, which increases protein breakdown. Increased protein breakdown is a common feature of illness. Protein breakdown is stimulated by hormones (such as glucagon, epinephrine, and cortisol) and inflammatory cytokines [3, 4]
- Strenuous physical exercise, which results in muscle stress and protein turnover 
- Stress – An inappropriate increase in the activation of the sympathetic, renin-angiotensin-aldosterone, and vasopressin systems elevate BUN, which is often seen in heart failure. Cortisol will also increase protein breakdown and elevate BUN [21, 22]
- Gut bleeding – When upper GI bleeding occurs, the blood is digested to protein. This protein is transported to the liver and metabolized to BUN [3, 2]
- Poor circulation, which results in lower blood flow to the kidneys and therefore less of an ability to clear the urea [23, 4]
- Thyroid conditions, which result in abnormal kidney function: hypothyroidism, and hyperthyroidism [24, 25]
- Anti-anabolic drugs such as glucocorticoids andtetracyclines (except doxycycline) 
- Lowergrowth hormone orIGF-1. IGF-1 and growth hormone inhibit urea synthesis 
- Inborn errors of metabolism (genetic urea cycle disorders) 
Factors that Decrease Urea Levels
High urea levels may indicate an underlying health problem that requires medical attention. Rather than trying to artificially decrease urea, work with your doctor to diagnose and treat any condition that may be causing high urea. You may also try the following strategies if your doctor determines that they are appropriate.
Your doctor may check if any environmental or dietary factors could be causing high urea levels. Among these are dehydration and a very high protein diet. If one or both of these are determined to be the underlying cause, you would ly be advised to:
- Drink more water (stay properly hydrated)
- Eat less protein
Because people with high BMI are more ly to experience kidney dysfunction, weight loss may help improve kidney health and lower urea levels [26, 27, 28].
A few supplements have also been found to decrease urea and possibly improve kidney function in animals. However, no clinical studies exist to support the use of these supplements to combat high blood urea or kidney dysfunction. Talk to your doctor before adding any new supplements, and never use these in place of what your doctor prescribes.
Blood Urea Nitrogen (BUN) – Understand the Test
Sources Used in Current Review
2019 review performed by Richa Athalye and the Lab Tests Online Editorial Review Board.
(April 15, 2019) MedlinePlus. Blood Urea Nitrogen. Available online at https://medlineplus.gov/lab-tests/bun-blood-urea-nitrogen/. Accessed August 2019.
(March 6, 2014) Medscape Reference. Blood Urea Nitrogen (BUN). Available online at https://emedicine.medscape.com/article/2073979-overview. Accessed August 2019.
Blood urea nitrogen (BUN), serum. Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/81793. Accessed August 2019.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
(2002 March). Medical Tests of Kidney Function. National Kidney and Urologic Diseases Information Clearinghouse, NIH Publication No. 02–4623 [On-line information]. Available online at http://kidney.niddk.nih.gov/kudiseases/pubs/kidneytests/index.htm.
Esson, M. and Schrier, R. (2002). Diagnosis and Treatment of Acute Tubular Necrosis. Ann Intern Med 2002;137:744-752 [On-line journal]. PDF available for download at http://www.annals.org/cgi/reprint/137/9/744.pdf.
Agha, Irfan (2003 August 7, Updated). BUN. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003474.htm.
Agrawal, M. and Swartz, R. (2000 April 1). Acute Renal Failure. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20000401/2077.html.
Physician’s Reference Laboratory: Kidney Function Panel. Available online at http://www.prlnet.com/Kidney.htm.
August 2007) National Kidney and Urological Disease Information Clearinghouse (NKUDIC). Your Kidneys and How They Work. Available online at http://www.kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/index.htm#rate. Accessed November 2008.
(Update May 15, 2007) MedlinePlus Medical Encyclopedia. BUN. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003474.htm. Accessed November 2008.
American Urological Association. UrologyHealth.org, Kidney (renal) Failure. Available online at http://www.urologyhealth.org/adult/index.cfm?cat=02&topic=120#top. Accessed November 2008.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pp. 312-313.
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006 Pp. 525-527.
Lerma, E. (Updated 2012 October 30). Blood Urea Nitrogen (BUN). Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2073979-overview. Accessed November 2012.
Dugdale, D. (2011 May 30). BUN – blood test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003474.htm. Accessed November 2012.
(© 1995-2012). Blood Urea Nitrogen (BUN), Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/81793. Accessed November 2012.
(Updated 2012 March 23). The Kidneys and How They Work. National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) [On-line information]. Available online at http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/. Accessed November 2012.
McMillan, J. (Modified 2010 January). Chronic Kidney Disease. Merck Manual for Healthcare Professionals [On-line information]. Available online through http://www.merckmanuals.com. Accessed November 2012.
Arora, P. (Updated 2012 March 28). Chronic Kidney Disease. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/238798-overview. Accessed November 2012.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 993-995.
Understanding Your Lab Values
People who develop chronic kidney disease may have some or all of the following tests and measurements. If you have kidney disease ask your doctor which tests you will have and how often they will be done. Speak to your doctor about your results. If your numbers are not in the normal range, ask how to improve them.
Serum Creatinine: Creatinine is a waste product in your blood that comes from muscle activity. It is normally removed from your blood by your kidneys, but when kidney function slows down, the creatinine level rises. Your doctor should use the results of your serum creatinine test to calculate your GFR.
Glomerular Filtration Rate (GFR): Your GFR tells how much kidney function you have. It may be estimated from your blood level of creatinine.
If your GFR falls below 30 you will need to see a kidney disease specialist (called a nephrologist). A GFR below 15 indicates that you need to start a treatment for kidney failure.
Your kidney disease specialist will speak to you about treatments for kidney failure, such as dialysis or kidney transplant.
Blood Urea Nitrogen (BUN): Urea nitrogen is a normal waste product in your blood that comes from the breakdown of protein from the foods you eat and from your body metabolism. It is normally removed from your blood by your kidneys, but when kidney function slows down, the BUN level rises. BUN can also rise if you eat more protein, and it can fall if you eat less protein.
Urine Protein: When your kidneys are damaged, protein leaks into your urine. A simple test can be done to detect protein in your urine. Persistent protein in the urine is an early sign of chronic kidney disease.
Microalbuminuria: This is a sensitive test that can detect a small amount of protein in the urine.
Urine Creatinine: This test estimates the concentration of your urine and helps to give an accurate protein result. Protein-to-Creatinine Ratio: This estimates the amount of protein you excrete in your urine in a day and avoids the need to collect a 24-hour sample of your urine.
Serum Albumin: Albumin is a type of body protein made from the protein you eat each day.
A low level of albumin in your blood may be caused by not getting enough protein or calories from your diet.
A low level of albumin may lead to health problems such as difficulty fighting off infections. Ask your dietitian how to get the right amount of protein and calories from your diet.
nPNA: Your nPNA (normalized protein nitrogen appearance) is a test that may tell if you are eating enough protein. This measurement comes from lab studies that include a urine collection and blood work. Your dietitian may ask for an accurate food record to go with this test.
Subjective Global Assessment (SGA): Your dietitian may use SGA to help check for signs of nutrition problems. The dietitian will ask you some questions about your daily diet and check your weight and the fat and muscle stores in your face, hands, arms, shoulders and legs. Ask your dietitian about your score on the SGA. If your score is too low, ask how to improve it.
Hemoglobin: Hemoglobin is the part of red blood cells that carries oxygen from your lungs to all parts of your body.
Your hemoglobin level tells your doctor if you have anemia, which makes you feel tired and have little energy. If you have anemia, you may need treatment with iron supplements and a hormone called erythropoietin (EPO).
The goal of anemia treatment is to reach and maintain a hemoglobin level of at least 11 to 12.
Hematocrit: Your hematocrit is a measure of the red blood cells your body is making. A low hematocrit can mean you have anemia and need treatment with iron and EPO. You will feel less tired and have more energy when your hematocrit reaches at least 33 to 36 percent.
TSAT and Serum Ferritin: Your TSAT (pronounced tee-sat) and serum ferritin (pronounced ferry-tin) are measures of iron in your body. Your TSAT should be above 20 percent and your serum ferritin should be above 100. This will help you build red blood cells. Your doctor will recommend iron supplements when needed to reach your target levels.
Parathyroid Hormone (PTH): High levels of parathyroid hormone (PTH) may result from a poor balance of calcium and phosphorus in your body. This can cause bone disease.
Ask your doctor if your PTH level is in the right range. Your doctor may order a special prescription form of vitamin D to help lower your PTH.
Caution: Do not take over-the-counter vitamin D unless ordered by your doctor.
Calcium: Calcium is a mineral that is important for strong bones. Ask your doctor what your calcium level should be. To help balance the amount of calcium in your blood, your doctor may ask you to take calcium supplements and a special prescription form of vitamin D. Take only the supplements and medications recommended by your doctor.
Phosphorus: A high phosphorus level can lead to weak bones. Ask your doctor what your phosphorus level should be. If your level is too high, your doctor may ask you to reduce your intake of foods that are high in phosphorus and take a type of medication called a phosphate binder with your meals and snacks.
Potassium: Potassium is a mineral in your blood that helps your heart and muscles work properly. A potassium level that is too high or too low may weaken muscles and change your heartbeat.
Whether you need to change the amount of high- potassium foods in your diet depends on your stage of kidney disease. Ask your doctor what your potassium level should be.
Your dietitian can help you plan your diet to get the right amount of potassium.
Body Weight: Maintaining a healthy weight is important to your overall health. If you are losing weight without even trying, you may not be getting the right nutrition to stay healthy. Your dietitian can suggest how to safely add extra calories to your diet if needed.
On the other hand, if you are slowly gaining too much weight, you may need to reduce calories and increase your activity level. A sudden weight gain can also be a problem. If it is accompanied by swelling, shortness of breath and a rise in blood pressure, it may be a sign of too much fluid in your body.
Speak to your doctor if your weight changes noticeably.
Blood Pressure: Ask your doctor what your blood pressure should be. If your blood pressure is high, make sure to follow all the steps in your prescribed treatment, which may include taking high blood pressure medications, cutting down on the amount of salt in your diet, losing excess weight and following a regular exercise program.
Total Cholesterol: Cholesterol is a fat- substance found in your blood. A high cholesterol level may increase your chance of having heart and circulation problems.
For many patients, a good level for total cholesterol is below 200. If your cholesterol level is too high, your doctor may ask you to make some changes in your diet and increase your activity level.
In some cases, medications are also used.
HDL Cholesterol: HDL cholesterol is a type of “good” cholesterol that protects your heart. For many patients, the target level for HDL cholesterol is above 40.
LDL Cholesterol: LDL cholesterol is a type of “bad” cholesterol. A high LDL level may increase your chance of having heart and circulation problems. For many patients, the target level for LDL cholesterol is below 100. If your LDL level is too high, your doctor may ask you to make some changes in your diet and increase your activity level.
Triglyceride: Triglyceride is a type of fat found in your blood. A high triglyceride level along with high levels of total and LDL cholesterol may increase your chance of heart and circulation problems.
BUN levels: Measurements, results, and procedure
A BUN test measures the level of urea nitrogen in the blood using a standard blood sample.
BUN stands for blood urea nitrogen, which is a natural byproduct of the breakdown of protein.
According to the American Association for Clinical Chemistry, doctors perform BUN tests to assess kidney health. However, altered BUN counts can result from almost any disease, drug, or condition that causes changes in the kidneys or liver.
Due to the variety of conditions a BUN test can indicate, a doctor may recommend a BUN test as part of routine check-ups. BUN tests are part of standard blood tests, such as metabolic panels.
Healthcare professionals use BUN tests for a variety of reasons, including monitoring kidney and liver function.
The liver and kidneys influence BUN levels profoundly, as they are responsible for breaking down protein and managing the waste.
The liver produces urea as part of the body’s process of breaking down protein. The liver releases urea into the blood, and it travels to the kidneys for removal in the urine. Urea contains nitrogen and is also the compound responsible for helping clear excess nitrogen from the body.
For this reason, people often refer to both “urea” and “urea nitrogen” as the same compound. This is not technically correct, but the two go hand-in-hand and measuring the level of this in the bloodstream helps to give a reliable indication of kidney and liver health.
A component of many other blood tests, a doctor can order a BUN test for any person, even if they have no apparent symptoms or underlying conditions. A doctor will most often request a BUN test along with other related lab tests if they suspect kidney or liver diseases.
Kidney and liver conditions are common in adults, but they are easy to overlook or mistake for other disorders.
The BUN test requires only a blood sample. A doctor may carry out a BUN test alongside other kidney tests, such as the serum creatinine test.
Symptoms of liver and kidney disease
According to the Centers for Disease Control and Prevention (CDC), an estimated 15 percent of adults in the United States have long-term kidney disease, known as chronic kidney disease. Many people are unaware that they have the condition.
Symptoms of kidney disease include:
- frequent urination, especially at night
- change in urine volume
- decreased need to urinate
- a burning sensation during urination
- brown or red urine that appears foamy
- pain, especially in the area near the kidneys (flank region)
- muscle cramps
- numbness in the hands and feet
- interrupted sleep
- tiredness and a lack of concentration or alertness
- poor appetite
- swelling or puffiness, especially around the face, wrists, ankles, abdomen, and thighs
- high blood pressure
Symptoms of liver disease include:
- dark colored urine
- pale-colored stool
- skin and whites of the eyes that appear yellow
- bruising easily
- loss of appetite
- nausea or vomiting
- weight loss or gain
- ongoing tiredness or weakness
- abdominal pain and swelling
- swelling in the legs and ankles
Preparing for a BUN test is relatively straightforward.
Those having a BUN test should eat and drink as usual before the test. This helps ensure that results accurately reflect levels as they usually are.
Tell the doctor about any medications or supplements taken before or on the day of the test.
To perform the BUN test, a healthcare professional draws blood from a vein. They will often use a vein in front of the elbow or the back of the hand.
Laboratory technicians will then examine the blood sample and send the results to the individual’s doctor.
After the test, most people return to their usual routine. However, some people may also feel faint, hungry, or dehydrated.
If the area around the draw site becomes painful, inflamed, or starts to discharge pus or excess blood, the person should seek medical attention.
Share on PinterestBUN tests show how much nitrogen is the blood/
A BUN test that demonstrates a rise or fall in blood urea nitrogen levels might indicate a wide range of health problems.
This is because the kidneys and liver are involved in a vast scope of bodily functions, and problems elsewhere in the body that affect kidneys or liver function can also end up leading to an abnormality in the BUN level.
General reference ranges for a normal BUN level are as follows:
- Adults up to 60 years of age: 6-20 mg/dL
- Adults over 60 years of age: 8-23 mg/dL
However, these ranges will ly vary from lab to lab. If you are significantly outside the normal range at the lab your blood is sent to, it could be due to underlying kidney or liver disease.
The following factors can lead to elevated BUN levels:
Low BUN levels, which are not common, can result from:
- liver failure
- not consuming enough protein in the diet due to poor nutrition or a very low-protein diet
Typically, BUN levels increase with age. Changes in BUN levels also occur and during pregnancy.
The ideal range of BUN values might vary the person’s age and the reference range that the laboratory uses. People should speak to their doctor about what their results mean.
Certain over-the-counter (OTC) painkillers, in particular, non-steroidal anti-inflammatory drugs (NSAIDs), can all adversely affect the kidneys. This class of drugs includes ibuprofen, naproxen, and aspirin.
Natural diuretics, such as caffeine, and prescription diuretics can also affect the kidneys. Antibiotics can also impact BUN levels.
Many prescription drugs can affect the kidneys, some less frequently than others, resulting in abnormal BUN levels, including:
- amphotericin B
- sulfonamide antibiotics
According to the National Kidney Foundation, herbal supplements can also adversely affect the kidneys of people with kidney disease.
Generally, the U.S. Food and Drug Administration (FDA) does not regulate natural health products. This means that the effective dosage, source, and even the precise mixture of the supplement are uncertain.
This lack of regulation also means herbal supplements may contain compounds that damage the kidneys, such as heavy metals or aristolochic acid.
People with kidney or liver disease should also limit or monitor phosphorous and potassium intake.
Share on PinterestBUN tests can provide a picture of kidney health but not diagnose a disease.
BUN testing alone is not enough to diagnose any condition. It may merely highlight the need for further, more specific testing.
If BUN results come back higher or lower than usual, a healthcare professional will usually follow up with other tests. A serum creatinine test combined with the BUN level can help highlight particular conditions.
A doctor may also carry out testing to measure the blood levels of specific electrolytes, such as potassium, sodium, and calcium, as well as ordering urine tests.
Commonly, a serum chemistry panel is ordered, which typically measures the levels of BUN, creatinine, and electrolytes.
In some instances, doctors may also follow up abnormal BUN results by evaluating the BUN-to-creatinine ratio in the bloodstream.
Creatinine is a waste product that occurs after the muscles break down creatine. Creatine is a product of amino acid metabolism made after protein breakdown, and it is necessary for the body, helping to produce energy and move the muscles.
The ratio of BUN to creatinine is usually between 10:1 and 20:1.
The course of treatment for each person with abnormal BUN levels varies depending on the cause and severity. Less serious health issues that lead to abnormal BUN levels might require less intense therapy and long-term monitoring.
People with more severe conditions, such as end-stage kidney disease, often need intensive and on-going treatment, such as dialysis.
In the case of abnormal BUN levels caused by eating too much protein, people can limit the amount of protein-rich foods, such as meat, fish, beans, and dairy, and increase the amount of fruit and vegetables they consume. Staying well-hydrated also helps prevent the buildup of BUN.
According to a 2014 cross-sectional study, a person with high BUN levels is more ly to have high blood pressure.
A 2014 survey of over 1 million military veterans from the U.S. linked high BUN levels with an increased risk of diabetes mellitus.
BUN tests are easy to perform and may be a useful indicator of overall health and kidney and liver function.
What lifestyle changes can I make to return BUN levels to normal?
If you have elevated BUN levels, you will need to work with your doctor to help determine the cause, which could be a minor complaint or a more serious condition.
For instance, if your BUN is too high from not being well-hydrated, make time in your day to try to drink more water. Another possibility is that your diet may not be well-balanced. You can work with your physician or a dietician to choose a diet that is right for you.
If a more significant underlying medical process is causing your BUN to be too high, your physician can work with you to develop a treatment plan to best address and treat this.
Stacy Sampson, DO Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.