BUN - blood test

Definition

BUN stands for blood urea nitrogen. Urea nitrogen is what forms when protein breaks down.

A test can be done to measure the amount of urea nitrogen in the blood.

Alternative Names

Blood urea nitrogen; Renal insufficiency - BUN; Renal failure - BUN; Renal disease - BUN

How the Test is Performed

A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.

How to Prepare for the Test

Many medicines can interfere with blood test results.

• Your health care provider will tell you if you need to stop taking any medicines before you have this test.
• DO NOT stop or change your medicines without talking to your provider first.

How the Test will Feel

You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.

Why the Test is Performed

The BUN test is often done to check kidney function.

Normal Results

The normal result is generally 6 to 20 mg/dL.

Note: Normal values may vary among different labs. Talk to your provider about your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean

Higher-than-normal level may be due to:

• Congestive heart failure
• Excessive amount of dietary protein in the gastrointestinal tract
• Gastrointestinal bleeding
• Hypovolemia (dehydration)
• Heart attack
• Kidney disease, including glomerulonephritis, pyelonephritis, and acute tubular necrosis
• Kidney failure
• Shock
• Urinary tract obstruction

Lower-than-normal level may be due to:

• Liver failure
• Low protein diet
• Malnutrition
• Over-hydration

Considerations

For people with liver disease, the BUN level may be low even if the kidneys are normal.

References

Landry DW, Bazari H. Approach to the patient with renal disease. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 106.

Oh MS, Breifel G, Pincus MR. Evaluation of renal function, water, electrolytes, and acid-base balance. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 15.

Weisbord SD, Palevsky PM. Prevention and management of acute kidney injury. In: Yu ASL, Chertow GM, Luyckx VA, Marsden PA, Skorecki K, Taal MW, eds. Brenner and Rector's The Kidney. 11th ed. Philadelphia, PA: Elsevier; 2020:chap 29.