Blood Urea Nitrogen (BUN) Test

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WHAT IS BLOOD UREA NITROGEN (BUN) TEST? A blood urea nitrogen test is a medical urea blood test that measures the amount of urea nitrogen present in your blood.  Urea is made when protein is broken down in your liver and passed out of your body by being in the urine. A BUN blood test… Read More

Blood Urea Nitrogen (BUN) Test


A blood urea nitrogen test is a medical urea blood test that measures the amount of urea nitrogen present in your blood. 

Urea is made when protein is broken down in your liver and passed out of your body by being in the urine. A BUN blood test is done to see how well your kidneys are performing. Normal human adult blood contains 6─20mg/dL of urea nitrogen.


A urea blood test for nitrogen is used to see if your kidney is working properly. It can also help in diagnosing certain other health conditions. 

BUN blood test uses include:

  • Primarily, to evaluate kidney function.
  • To diagnose liver damage.
  • To diagnose malnutrition.
  • To diagnose poor blood circulation.
  • To diagnose dehydration.
  • To diagnose urinary tract obstruction.
  • To diagnose congestive heart failure.
  • To diagnose gastrointestinal bleeding.
  • To determine the effectiveness of dialysis treatment.
  • Regular medical checkups during or after treatments such as diabetes.


If your doctor suspects that you have kidney problems, he/she may order a BUN blood test. These symptoms are, or may include:

  • A change in how much you urinate.
  • Having pains while you urinate.
  • Urine that is foamy, bloody, brown, or discolored.
  • Pain in your mid-back.
  • Frequent tiredness.
  • Swelling in your arms, ankles, legs, face, abdomen, or around your eyes.
  • Restless legs during sleep.
  • Weight loss.
  • Abnormal heart rhythms.
  • Kidney damage.
  • Shortened breaths.
  • Muscle cramps.
  • Itching.
  • Nausea.
  • Vomiting.
  • Hypertension.
  • Anemia.
  • Decreased mental alertness.
  • Sleeping difficulty.


A BUN blood test does not require any special preparation. If the test is to determine only urea nitrogen in the blood, you may eat normally before the test. However, it should be noted that if your blood sample will be used for additional tests, you may need to fast for a prescribed time before the test. 

Your doctor will give you specific instructions. Tell your doctor if you are on medication because certain medications can affect your BUN levels.


The medications that can cause low BUN levels to include:

  • Chloramphenicol.
  • Streptomycin. (etc)

The medications that can cause high BUN levels to include:

  • Amphotericin B (AmBisome, Fungizone).
  • Carbamazepine (Tegretol).
  • Furosemide (Lasix).
  • Methotrexate.
  • Cephalosporins; a group of antibiotics.
  • Methyldopa.
  • Rifampin (Rifadin).
  • Tetracycline (Sumycin).
  • Spironolactone (Aldactone).
  • Vancomycin (Vancocin).
  • Thiazide diuretics.


A blood urea test for nitrogen is a simple test. It involves taking a small blood sample and sending it to the laboratory for analysis. It is carried out by a medical laboratory technician.

  • Before drawing the blood, the technician will clean an area of your upper arm, where the blood is to be taken, with an antiseptic.
  • He/she ties an elastic band around your arm, which makes your veins swell with blood.
  • He/she then insects a sterile needle into a vein and draws the blood into a tube attached to the needle. You may feel mild pain when the needle goes in.
  • He/she removes the needle when enough blood is collected and applies pressure with cotton wool or bandage over the puncture site.
  • Your blood sample is then sent to a lab for testing.
  • The lab sends the test result to your doctor, who will study the BUN creatinine ratio and discuss the result with you.


The results of a BUN test depend on gender and age. The result is measured in milligrams per deciliter (mg/dL). Normal BUN levels tend to vary, depending on gender and age. However, in general, blood urea normal range includes the following:

  • Adult man = 8─24mg/dL
  • Adult woman = 6─21mg/dL
  • Children (1─17 years) = 7─20mg/dL

It is important to note that normal BUN levels for adults over 60 years are slightly higher than normal levels for below 60 years. 

SYMPTOMS OF HIGH BUN LEVELS (Blood Urea Nitrogen High)

  • Shock.
  • Stress.
  • Dehydration.
  • Heart disease.
  • Kidney failure.
  • Kidney disease.
  • High protein levels. 
  • Recent heart attack.
  • Congestive heart failure.
  • Gastrointestinal bleeding.
  • Obstruction in the urinary tract.
  • Medications, such as certain antibiotics and diuretics.

SYMPTOMS OF LOW BUN LEVELS (Blood Urea Nitrogen Low)

  • Liver failure.
  • Malnutrition.
  • Severe lack of protein in your diet.
  • Over-hydration (too much fluid in your system).


Please note that abnormal BUN levels do not always mean a poor kidney condition. Sometimes, certain factors such as the below can affect your urea nitrogen levels, without indicating a health risk:

  • Aging.
  • Steroids.
  • Pregnancy.
  • Medications.
  • Dehydration.
  • Low protein intake.
  • High protein intake.


BUN blood tests are not associated with serious risks or side effects. Nevertheless, taking medications like blood thinners can cause you to bleed more than expected during the test. Minor side effects may include:

  • Bruising at the puncture site.
  • Bleeding at the puncture site.
  • Infection at the puncture site.
  • Accumulation of blood under the skin.
  • Rarely fainting may occur after the blood drowns.

Please always be careful about your health; report any prolonged side effects to your doctor.

Depending on your blood urea test results, your doctor may also run other tests to confirm a diagnosis or recommend treatment. 

Possible additional tests your doctor may recommend include a creatinine test. In some cases, an abnormal BUN level isn’t an indicator of a kidney problem. Certain conditions can lead to high or low BUN levels, such as dehydration, pregnancy, medications, etc.


  • What levels of BUN indicate kidney failure?

BUN indicates that urea nitrogen is produced in the body during protein breakdown. There is no definite value of BUN that would diagnose kidney failure.

  • What does it mean if my BUN is high?

A high BUN value can mean kidney injury or disease is present. Kidney damage can be caused by diabetes or high blood pressure that directly affects the kidneys. High BUN levels can also be caused by dehydration or heart failure. Many medicines may cause a high BUN.

  • What are the symptoms of high BUN levels?

The symptoms of high BUN levels include itching, frequent urination, recurring fatigue, swelling (in the arms, legs, or feet), muscle cramps, insomnia, etc.

  • What is considered a high BUN level?

In general, around 7─20mg/dL (2.5─7.1mmol/L) is considered a normal BUN level. 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 alternative or additional tests can be done to confirm a BUN test if in doubt?

If your healthcare provider suspects you have kidney disease, additional tests may be recommended. These may include a measurement of creatinine (which is another waste product filtered by your kidneys), as well as a test called a GFR (Glomerular Filtration Rate).