woman sitting on bed in pain due to knee joint pain

BUN Levels: Low And High Ranges

March 19, 2020

When it comes to testing the function of the kidneys, one test that is requested by physicians is the BUN or blood urea nitrogen test. This test determines if the BUN levels are normal, low, or high. With regards to the BUN test, here is what you need to understand along with its associated risks and the expected results.

Blood Urea Nitrogen (BUN) Test

Nitrogen is present in the blood which comes from urea, a waste product that is made due to the breakdown of protein. Urea is manufactured in the liver and is excreted from the body via urine. When it comes to measuring the amount of nitrogen and urea in the blood, a BUN test is done.

Furthermore, a BUN test evaluates kidney function. When the kidneys are unable to eliminate urea from the blood, then the BUN levels are high. A diet high in protein, dehydration, and heart failure are also other factors that cause an elevated BUN level. On the other hand, low BUN levels are due to liver damage or disease. A pregnancy that is in its third or second trimester may also result in a low BUN level.


When Is It Done?

A BUN test is usually part of a checkup. However, some doctors require this test, especially if he suspects that an individual has a kidney disorder and manifests the symptoms mentioned below.

  • Urine That is Brown, Discolored, Bloody, or Foamy
  • Change in Amount of Urine Passed
  • Pain While Urinating
  • Swelling Face, Abdomen, Wrists, Legs, Ankles, or Arms
  • Bone or Joint Pain
  • Pain in Mid-Back
  • Feeling of Tiredness


Preparing for BUN Test

If you are taking any medications, then your doctor will advise that you discontinue them before the blood test. Your doctor may also recommend that you fast before the blood test. However, if you are only set to get the BUN test, you may still consume food and drinks.


Since the procedure is done by a licensed healthcare provider, there are little risks involved when blood is taken from the vein. However, the area where blood was taken may manifest bruising. Lower the risk of bruising by placing pressure on the area for a few minutes.

In rare instances, the vein where blood was taken appears swollen. Such a condition is known as phlebitis which is easily treated via a warm compress. This compress should be applied to the area several times a day.

Results of BUN Test

The values of a BUN test will determine the state of the kidneys.

1. Normal Values

Normal BUN levels are 7 to 30 mg/dL or 2.5 to 7.1 mmol/L. However, such values vary from one lab to the next. The reference range serves as a guide.

  • Adults Above the Age of 60: 8 to 23 mg/dL
  • Adults Up to the Age of 60: 6 to 20 mg/dL
  • Children: 5 to 18 mg/dL


2. High Values

If the values are higher than the reference range, then it could indicate kidney disease or injury. Damage to the kidneys is likely a result of high blood pressure or diabetes. It may also be due to low blood circulation to the kidneys because of heart failure or dehydration.

Other than medical conditions, high BUN levels are also because of medications and a diet that is high in protein. Tissue damage, bleeding in the gastrointestinal tract, and Addison’s disease may also lead to high levels of BUN. Elevated levels of BUN might also be due to the following factors.

  • Shock
  • High Cholesterol
  • Intense Stress
  • Obesity
  • Urinary Tract Disease or Blockage

Lowering the BUN values involves cutting back on protein-rich food and eating more fiber. Chitosan supplements are also recommended since it aids in reducing Cholesterol and shedding extra weight.

3. Low Values

Take note that low BUN values are not a good thing. If the amounts are smaller than the reference range, then this may likely indicate overhydration or a diet that contains little to no protein. Other conditions that cause low BUN levels include syndrome of inappropriate antidiuretic hormone secretion or SIADH, cirrhosis, pregnancy, or severe muscle injury (rhabdomyolysis).

Children and women are likely to have a low BUN level due to their body’s ability to breakdown protein. Severe liver damage and malnutrition are also other factors that lead to low BUN values. Raising BUN values involve consuming a diet rich in protein and lessening the amount of water consumed.

Follow-Up Tests

Take note, however, that a BUN test is not the only method used to diagnose the condition of the kidneys. Other tests are recommended as a follow-up to a BUN test. These include blood tests for specific electrolytes like calcium, sodium, and potassium.

A serum creatinine test is also requested. Another test ordered includes a serum chemistry panel that measures the electrolyte, creatinine, and BUN levels. The GFR test or glomerular filtration rate test is also done since it estimates the function of the kidneys when it comes to filtering blood.

Other tests to determine healthy kidney function include imaging tests like a CT scan and an ultrasound; urine tests which include a urinalysis, urine protein, microalbuminuria, and creatinine clearance.

Treatment for Abnormal BUN Values

Depending on the severity as well as the cause of abnormal BUN values, the treatment varies. Health issues that result in irregular BUN values that are less serious may require short-term monitoring and less intense therapy.

On the other hand, individuals who suffer from severe medical conditions like end-stage kidney disease require long-term treatment. This is likely to involve dialysis. As for BUN values that are high due to excessive protein in the diet, a doctor would recommend removing protein-rich food and instead of adding vegetables and fruits. Consuming the required amount of water in a day also prevents BUN buildup.

Keeping the BUN values regular ensures that the kidneys are healthy and functioning well. Speak to your doctor regarding methods for maintaining optimal kidney health. Moreover, sticking to average BUN values slows down the progression of kidney disorders in individuals affected.


Bun Test: When Is It Done?