Laboratory test: blood urea nitrogen, BUN level (2023)


    • blood urea nitrogen (BUN serum)


    • Measurement of serum or plasma blood urea nitrogen (BUN) to assess and treat volume status and kidney disease. It is performed on patients undergoing routine laboratory testing and is usually performed as part of a multi-phase automated testing procedure.

    reference range

    • Adults: 10-20 mg/dl (3.6-7.1 mmol/l)
    • Elderly: may be slightly higher than adults
    • Kinder: 5-18 mg/dl (1,8-6,4 mmol/l)
    • Infant: 5-18 mg/dl
    • Newborns: 3-12 mg/dl
    • String: 21-40 mg/dL
    • Critical values: >100 mg/dL (indicates severe impairment of kidney function)
    (Video) Introduction to Blood Urea Nitrogen (BUN) Test – Med-Surg | Lecturio Nursing

    Indications & Uses

    • Adrenal insufficiency - Moderate elevations in BUN levels are consistent with both acute and chronic adrenal insufficiency. The raised bun is largely due to dehydration as a result of aldosterone deficiency, which leads to excretion of too much sodium and leads to azotemia. Patients with secondary adrenal insufficiency are less affected due to intact aldosterone secretion. The increase is usually reversible when normal renal hemodynamics and circulatory blood volume are restored.
    • Community-acquired pneumonia - In one study, increased BUN, along with increased respiratory rate and decreased diastolic blood pressure, was predictive of mortality in patients with community-acquired pneumonia.
    • Hemolytic uremic syndrome (HUS) - BUN levels are consistently elevated, and the elevation is usually very rapid. The combination of renal insufficiency, acatabolic state, and reabsorption of blood from the gastrointestinal tract can result in an increase in BUN levels of up to 50 mg/dL/day. In children with uncomplicated dehydration and diarrhea, BUN levels should fall to half of intake levels within 24 hours; if this does not occur, kidney disease should be suspected.
    • Hemorrhagic shock – Acute tubular necrosis (ATN) from prolonged hypotension leads to renal failure. BUN and creatinine levels typically increase at a fixed 10:1 ratio for the first few days after shock. Elevated BUN levels also occur secondary to the breakdown of blood in the gastrointestinal tract, as seen in gastrointestinal bleeding and as a result of prerenal azotemia.
    • Initial assessment and monitoring of hyperosmolar hyperglycemic status - BUN is almost always elevated in HHS as a result of dehydration and kidney damage, even in the absence of significant diabetic nephropathy. The mean BUN level is 61 mg/dL in patients with HHS.
    • Initial assessment and monitoring for suspected diabetic acidosis - BUN levels are usually mildly to moderately elevated (mean 32 mg/dL) in diabetic ketoacidosis (DKA), reflecting significant volume depletion rather than diabetic nephropathy. CheckBUN every 2 to 4 hours until patient is stable.
    • Metabolic acidosis – Anion gap metabolic acidosis develops when the glomerular filtration rate is less than 20 mL/min (BUN levels above 40 mg/dL).
    • Sickle cell anemia - chronically elevated BUN levels associated with elevated serum creatinine, albeit slightly elevated, suggests renal insufficiency.
    • Suspected cardiogenic shock - increased BUN may occur as a result of pre-existing kidney disease or poor renal perfusion; Poor renal perfusion can eventually lead to prerenal azotemia or overt acute tubular necrosis (ATN) due to renal ischemia.
    • Suspected dehydration in children with acute gastroenteritis - BUN levels below 40 mg/dL may be associated with mild to moderate dehydration. BUN levels above 100 mg/dL can be associated with moderate to severe dehydration.
    • Suspected hypertensive crisis - BUN and creatinine levels tend to rise early in therapy but eventually improve as the renal arterioles recover from the effects of hypertension. The increase in BUN may be more rapid in patients with essential hypertension in the malignant phase than in patients with another underlying primary kidney disease.
    • Suspected necrotizing soft tissue infection – in one study, a BUN greater than 51 mg/dL was reported in 60% of cases of synergistic necrotizing cellulitis.
    • Suspected or known acute renal failure - BUN levels progressively increase at a rate of at least 10 mg/dL/day in clinically significant renal failure. In hospitalized patients with extensive tissue necrosis, it can increase at a rate of 50 to 100 mg/dL/day. A BUN of 50 to 100 mg/100 mL suggests serious renal dysfunction, and a BUN of 150 to 250 mg/100 mL is practically diagnostic of severe glomerular dysfunction. At steady state, a 50% decrease in glomerular filtration rate (GFR) results in a doubling of BUN.
    • Suspected or known renal failure – in patients without a history of renal disease, acute renal failure can be indicated by either a BUN of at least 40 mg/dL (14.3 mmol/L) or a serum creatinine level of at least 2 mg/dL (177 micromol/L). l). If GFR falls below 10 mL/min, serum creatinine should increase by 0.5 to 1.5 mg/dL (44 to 133 micromol/L) per day, depending on age, muscle mass, and muscle injury. BUN should increase by 10 to 20 mg/dL (3.6 to 7.1 mmol/L) per day, but the rate of increase may be higher in hypercatabolic conditions such as sepsis, gastrointestinal bleeding, or with use of corticosteroids.
    • Causes of rapid serial increases in BUN values:
      • Clinically significant renal failure (e.g. GFR < 10 mL/minute): increase of 10 to 20 mg/dL/day.
      • Extensive tissue necrosis: 50 to 100 mg/dL/day increase.
      • Hypercatabolic conditions (eg, sepsis, gastrointestinal bleeding, corticosteroid use)
    • Suspected sepsis - BUN levels may be elevated due to prerenal azotemia, drug toxicity in gastrointestinal bleeding, or ATN. The Infectious Disease Society of America recommends BUN and serum creatinine initially and at least every 3 days during intensive antibiotic therapy.
    • Suspected Toxic Shock Syndrome - BUN may be elevated as a result of myoglobinaemia or shock.
    • To differentiate between upper and lower acute gastrointestinal bleeding:
      • In patients with acute GI bleeding, a BUN:creatinine ratio of 36 or greater indicates an upper GI bleeding site.
      • In patients with GI bleeding and no kidney disease, a BUN above 40 mg/dL with normal creatinine levels indicates significant GI blood loss.
      • A BUN greater than 85 mg/dL with normal creatinine levels may indicate a loss of 2 or more units of blood to the gastrointestinal tract.
      • In patients with normal renal function, a slight increase in BUN (4 to 7 mg/dL above baseline) due to bleeding should resolve to normal within 24 hours. In patients with gastrointestinal bleeding, a sustained BUN elevation greater than 7 mg/dL above baseline is indicative of hypovolaemia, renal insufficiency, or ongoing bleeding.
      • In patients with acute GI bleeding, the absence of a BUN increase does not preclude an upper GI source of bleeding.
    • Suspected poststreptococcal glomerulonephritis - BUN is elevated to some degree in 60% to 75% of patients with poststreptococcal glomerulonephritis.

    Clinical Application

    The BUN measures the amount of urea nitrogen in the blood. Urea is formed in the liver as the end product of protein metabolism and digestion. The urea is deposited in the blood and transported to the kidneys for excretion. The BUN serves as an index for the function of the liver and kidneys. Patients with elevated BUN levels are said to have azotaemia or be azotemic.

    Almost all kidney diseases cause insufficient excretion of urea, which increases BUN. Since urea synthesis is dependent on the liver, severe liver disease can cause BUN to drop. Therefore, the BUN is directly related to the metabolic function of the liver and the excretory function of the kidney.

    The BUN is interpreted in conjunction with the creatinine test. These tests are called "kidney function studies." The BUN/creatinine ratio is a good measure of kidney and liver function. The normal adult range is 6 to 25, with 15.5 being the optimal value.

    Elevated Levels:

    (Video) Blood Urea Nitrogen (BUN) (Nursing Lab Values)

    Prerenal Causes:

    • Hypovolaemia, shock, burns, dehydration - with reduced blood volume, renal blood flow is reduced. Therefore, renal excretion of BUN is decreased and BUN levels increase.
    • Congestive heart failure myocardial infarction - with reduced heart function, decreased renal blood flow and increased BUN levels.
    • Gastrointestinal bleeding, excessive protein intake (tube feeding) - blood or dietary supplements overload the intestines with protein. Urea is increasingly formed and BUN accumulates.
    • Excessive protein catabolism and hunger – as proteins are broken down into amino acids at an accelerated rate, urea is formed at a higher rate and BUN accumulates.
    • Sepsis - renal blood flow and primary renal function are reduced for a variety of reasons. BUN levels rise.

    Kidney Causes:

    • Renal disease (eg, glomerulonephritis, pyelonephritis, acute tubular necrosis), renal failure, nephrotoxic drugs - primary renal disease are all associated with decreased BUN excretion.

    Posternale Azotemia

    • Ureteral obstruction due to stones, tumor, or congenital abnormalities, bladder outlet obstruction due to prostatic hypertrophy or cancer, or congenital bladder/urethral abnormalities - obstruction of urinary flow leads to decreased excretion and an increase in BUN levels.

    Niedrigere Level:

    • Liver failure – Reduced liver function is associated with reduced BUN levels.
    • Overhydration due to fluid overload syndrome or inappropriate ADH secretion (SIADH) - BUN is diluted by fluid overload.
    • Negative nitrogen balance (e.g. malnutrition, malabsorption) - in the case of protein deficiency, urea production and thus BUN is reduced.
    • Pregnancy – Early pregnancy is associated with increased water retention and BUN dilution.
    • Nephrotic syndrome - this syndrome is associated with a loss of protein in the urine. With protein deficiency, BUN is reduced.

    Related tests

    • Basic Metabolism Panel
    • Extensive metabolic panel
    • Enteral/Parenteral Nutrition Management Panel
    • General health panel
    • Hypertension Panel
    • Prenatal screening panel
    • kidney plate
    • transplant plate
    • Creatinine, blood - test of kidney function that does not depend on liver function.
    • Kreatinin-Clearance
    (Video) BUN (Blood Urea Nitrogen) What is it? What does it mean?

    Drug-laboratory interactions

    • Outcomes increased in: febrile illness, high protein diet, tube feeding, gastrointestinal bleeding, dehydrated patients
    • Results decreased in: low-protein diet, high-carbohydrate diet, overhydrated patients
    • To some extent, muscle mass determines BUN levels. Women and children tend to have lower BUN levels than men.
    • Advanced pregnancy can lead to elevated levels due to high protein metabolism.
    • Drugs that can cause elevated BUN levels include: allopurinol, aminoglycosides, cephalosporins, chloral hydrate, cisplatin, furosemide, guanethidine, indomethacin, methotrexate, methyldopa nephrotoxic drugs (eg, aspirin, amphotericin B, bacitracin, carbamazepine, colistin , gentamicin, methicillin, neomycin). , penicillamine, polymyxin B, probenecid, vancomycin), propranolol, rifampin, spironolactone, tetracyclines, thiazide diuretics and triamterene.
    • Drugs that can lead to decreased levels include: chloramphenicol and streptomycin.

    test tube required

    • Red top tube


    • Take a venous blood sample.
    • Avoid hemolysis.
    • Apply pressure or a pressure bandage to the venipuncture site and observe the site for bleeding.
    (Video) BUN [blood urea nitrogen] lab value, nursing considerations - free quiz

    storage and handling

    • The sample is stable for 24 hours at room temperature, several days at 4°C to 6°C and 2 to 3 months frozen.

    What to tell the patient before and after

    • Explain the procedure to the patient, and then say that fasting is not required.


    • LaGow B. et al., eds. PDR Laboratory Advisor. A comprehensive point-of-care guide to over 600 lab tests. first edition. Montvale, NJ: Thomson PDR; 2007
    • Pagana K, Pagana TJ Hrsg. Mosby's Manual ofDiagnostic and Laboratory Tests. 5thEd. St. Louis, Missouri. 2014.
    (Video) Blood Urea Nitrogen BUN Nursing Considerations, Normal Range, Nursing Care, Lab Values Nursing


What level of BUN indicates kidney failure? ›

What is the BUN level for kidney failure? A level surpassing the BUN normal range of 6-20 mg/dL indicates kidney problems. If your BUN test shows extreme results, it might signal kidney failure. For example, a BUN level of 75 mg/dL is highly considered alarming.

What level of BUN is concerning? ›

Typically, the ratio of BUN to creatinine should be between 10:1 and 20:1. If it's lower or higher than that, it may mean you have a problem with your kidneys or you may not be drinking enough water.

Should I worry about high BUN levels? ›

Higher than normal BUN levels may be a sign that your kidneys aren't working well. People with early kidney disease may not have any symptoms. A BUN test can help uncover kidney problems at an early stage when treatment can be more effective.

What does it mean if my BUN is low? ›

Low values

A low BUN value may be caused by a diet very low in protein, by malnutrition, or by severe liver damage. Drinking too much liquid may cause overhydration and cause a low BUN value. Women and children may have lower BUN levels than men because of how their bodies break down protein.

Does BUN indicate liver disease? ›

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.

Is it better to have high or low BUN? ›

BUN/Creatinine Ratio

Blood urea nitrogen (BUN) and creatinine tests can be used together to find the BUN-to-creatinine ratio (BUN:creatinine). In most cases, it's healthier to have a lower ratio of BUN to creatinine (10:1 to 20:1) [9].

Do BUN levels increase with age? ›

Moreover, BUN reference values increased with age in the healthy population up to around 70–86 years for both healthy adult males and females.

What would cause BUN to be high? ›

Generally, a high BUN level means your kidneys aren't working well. But elevated BUN can also be due to: Dehydration, resulting from not drinking enough fluids or for other reasons. Urinary tract obstruction.

What can cause BUN to be high? ›

High BUN levels may suggest that your kidneys aren't working as they should. However, even if your kidneys are working properly, you may have elevated BUN levels from the following: High-protein diet. Dehydration.

Does high BUN indicate diabetes? ›

Two-stage residual inclusion analyses showed that, independent of the impact of eGFR, every 10 mg/dL increase in BUN concentration was associated with increased risk of incident diabetes (1.15; 1.14-1.16). Thus, higher levels of BUN are associated with increased risk of incident diabetes mellitus.

Is it okay to have low BUN? ›

Low BUN levels are not common and are not a cause for concern. Occasionally, severe liver disease, malnutrition, or over-hydration can cause BUN levels to be unusually low; however, the BUN test is not typically used to diagnose or monitor these conditions.

Does low BUN mean 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.

Is BUN high or low with dehydration? ›

Dehydration generally causes BUN levels to rise more than creatinine levels. This causes a high BUN-to-creatinine ratio. Kidney disease or blockage of the flow of urine from your kidney causes both BUN and creatinine levels to go up.

What is the best thing to drink for your kidneys? ›

While plain water is the best drink for your kidneys, other fluids are perfectly acceptable, including coffee, green tea, low-potassium juices, and infused water. Avoid sweetened, carbonated beverages and coconut water.

What foods to avoid if urea is high? ›

Don't eat ham, bacon, sausage, hot dogs, lunch meats, chicken tenders or nuggets, or regular canned soup. Only eat reduced-sodium soups that don't have potassium chloride as an ingredient (check the food label.) Also, only eat 1 cup, not the whole can.

Does BUN indicate heart failure? ›

The blood urea nitrogen (BUN)/creatinine ratio is a strong prognostic indicator in patients with acute decompensated heart failure (ADHF).

Can fatty liver cause high BUN? ›

Blood urea nitrogen is elevated in patients with non-alcoholic fatty liver disease. Hepatogastroenterology.

Is a BUN of 20 good? ›

In general, about 7 - 20 mg/dL is a normal level. A higher than normal BUN level may be a sign that your kidneys are not working well. Your doctor will compare your BUN results along with other test results, such as creatinine and eGFR (estimated glomerular filtration rate), to decide on next steps.

Is a BUN of 21 high? ›

In general, around 6 to 24 mg/dL (2.1 to 8.5 mmol/L ) is considered normal. But normal ranges may vary, depending on the reference range used by the lab and your age. Ask your doctor to explain your results. Urea nitrogen levels tend to increase with age.

What level of BUN and creatinine requires dialysis? ›

Usually, when the creatinine clearance falls to 10-12 cc/minute, the patient needs dialysis.

What is the first stage of kidney failure? ›

In Stage 1 CKD, the damage to your kidneys is mild. Your kidneys are still working well, but you may have signs of kidney damage or physical damage to your kidneys. Stage 1 CKD means you have a normal estimated glomerular filtration rate (eGFR) of 90 or greater, but there is protein in your urine (i.e., your pee).

What can cause an elevated BUN? ›

A high BUN value may be caused by a high-protein diet, Addison's disease, or tissue damage (such as from severe burns), or from bleeding in the gastrointestinal tract. High BUN-to-creatinine ratios occur with sudden (acute) kidney problems, which may be caused by shock or severe dehydration.

What if my BUN is 20? ›

In general, about 7 - 20 mg/dL is a normal level. A higher than normal BUN level may be a sign that your kidneys are not working well. Your doctor will compare your BUN results along with other test results, such as creatinine and eGFR (estimated glomerular filtration rate), to decide on next steps.

What is normal BUN creatinine ratio for elderly? ›

The estimated normal range of BUN was 14-23 mg/dl both in male and female elderly subjects, and that of Cr was 0.9-1.3 mg/dl in male and was 0.7-1.1 mg/dl in female.

What is the alarming level of creatinine? ›

A creatinine level of more than 1.4 for men and more than 1.2 for women may indicate that there is something wrong with the kidneys. If creatinine levels are higher than normal, a healthcare provider may recommend other tests to assess the problem. Measuring GFR can help confirm a problem with the kidneys.

What is considered a high BUN creatinine level? ›

So, to summarize, the high BUN-Creatinine ratio, particularly if it is more than 20 and the person has a normal creatinine, usually indicates dehydration. However, if BUN and creatinine are both elevated significantly and the ratio is < 20, it may indicate an underlying kidney problem.


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