Blood Urea Nitrogen (BUN) Test

A BUN test is a routine test that is done as part of a comprehensive metabolic profile. It is also performed to evaluate the functioning of kidneys or when the following symptoms of kidney diseases are observed:

• Oedema (water retention) especially around the ankles, feet and face
• Dyspnoea (shortness of breath)
• Reduced urine output
• Haematuria (passing blood in urine)
• Weight loss
• Loss of appetite
• Tiredness
• Muscle cramps
• Malaise
• Headache
• Itchy skin
• Insomnia

Additionally, BUN test is suggested to people who are at a very high risk of developing kidney disease or in case of the following conditions:

• Long-standing diabetes
• Long-standing blood pressure problems
• Congestive heart failure
• Myocardial infarction (heart attack)
• Chronic kidney disease (at regular intervals)
• Monitoring the effectiveness of dialysis
• Evaluating kidney function before starting with certain medications

BUN test does not require any special preparations. However, certain drugs, such as chloramphenicol and streptomycin, are known to reduce BUN levels, while a wide range of drugs can elevate BUN levels. So, before you go for the test, make sure to inform the doctor about any medications/ supplements that you are taking. Similarly, BUN levels are also seen to vary during pregnancy.  If you are pregnant or suspect a pregnancy inform the doctor before the test.

It is a simple test that takes less than five minutes. An experienced laboratory specialist withdraws a blood sample from a vein in the individual's arm by inserting a small needle. The blood sample is collected in a sterile vial or a test tube and sent to a lab for testing. A momentary pricking pain is felt when the needle goes into the vein.

There is a minimal risk of light-headedness and bruising at the site of injection after this test. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the site of withdrawal of blood.

BUN levels are evaluated as milligrams/decilitre (mg/dL or millimoles/litre [mmol/L])

Normal results

Normal levels of BUN range as 7-20 mg/dL (2.5-7.1 mmol/L).

Abnormal results

High values:

High levels of BUN usually indicate that poor functioning of kidneys, which can be attributed to

• Acute kidney failure
• Chronic kidney disease (chronic renal failure)
• Congestive cardiac failure
• Shock
• A recent episode of heart attack
• Severe burns
• Dehydration
• Obstruction to urine flow probably due to kidney stones, enlarged prostate etc.
• Stress

In certain situations, for example, when a person is on a high protein diet, it results in increased breakdown of proteins, which, in return, increases the levels of BUN. This is not abnormal; rather, it is a physiological variation.

Low values:

A low value of BUN is not common and does not hold any significance either. BUN levels can be low in cases of severe malnutrition, liver disease and sometimes during an overhydration phase; however, it neither helps in concluding the diagnosis nor in monitoring these conditions.

BUN levels are usually tested along with creatinine levels to evaluate the functioning of the kidney. It helps in diagnosing kidney disease and in monitoring patients having acute or chronic kidney failure.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational perspective and is in no way a substitute for medical advice from a qualified doctor.