What Level of BUN Indicates Kidney Failure? Stages

Blood urea nitrogen (BUN) is used to assess kidney function. There is no definite BUN value that indicates kidney failure.

The normal range of BUN is between 7 and 20 mg/dL or 2.5 and 7.1 mmol/L, with slight variations between labs. A decline in kidney function can increase BUN levels. No specific BUN value fully diagnoses kidney failure.

BUN and creatinine tests can be combined to determine the BUN-to-creatinine ratio (BUN:creatinine), which is more specific. Additional tests may include glomerular filtration rate (GFR) and creatinine clearance. A high BUN value can be caused by factors unrelated to the kidneys, such as:

• High protein diet
• Burns
• Dehydration
• Hemorrhage
• Shock
• Heart diseases (e.g., congestive heart failure, recent heart attack)
• Certain medicines
• Older age

If your BUN levels consistently exceed the normal range, consult your doctor to determine the cause.

What are kidneys and kidney function tests?

Kidneys are vital organs that maintain fluid and electrolyte balance, control blood pressure, remove waste products, activate vitamin D, and regulate red blood cell levels. Tests such as blood urea, serum creatinine, BUN, GFR, creatinine clearance, urine proteins, urine microalbumin, serum electrolytes, and complete blood counts (CBC) assess kidney health.

QUESTION

What is BUN?

BUN is a parameter used to measure kidney function. It is also known as a urea nitrogen test and serum BUN. BUN reflects the urea nitrogen produced during protein breakdown, which is eliminated through urine.

Kidney diseases or damage can cause increased BUN, but it is less specific than GFR and creatinine clearance. BUN values can vary independently of kidney function.

BUN values may decrease with a low-protein diet or increase with a high-protein diet. Other factors that could raise BUN include internal bleeding, injuries, glucocorticoid therapy, and liver diseases.

Why is a BUN test done?

A BUN test may be part of a routine checkup or ordered due to factors that increase the risk of kidney diseases, such as family history, high blood pressure, diabetes, kidney diseases, or long-term medication use. Symptoms of kidney diseases may also prompt a BUN test, including swelling, changes in urine, trouble sleeping, dry and itchy skin, fatigue, and reduced appetite.

What happens during a BUN test?

A BUN test is a quick procedure that involves obtaining a blood sample from a vein in the arm. The blood is collected in a special vial, and results are usually available within 24 to 48 hours.

What are the signs and symptoms of kidney failure?

Symptoms of kidney failure may be minimal in early stages and include decreased urine output, shortness of breath, disorientation, and swelling. Other symptoms can develop as kidney failure progresses and may include anemia, bad breath, bone pain, changes in skin color, confusion, easy bruising, fatigue, headaches, high blood pressure, itchy and dry skin, lack of concentration, muscle twitches and weakness, nausea, numbness and tingling, seizures, trouble sleeping, weakened bones, and weight loss.

What is the first stage of kidney failure?

The first stage of kidney failure is characterized by very mild kidney damage and normal kidney function. No symptoms are present, but tests may reveal indications of kidney damage.

Understanding the stages of kidney failure

Kidney failure has five stages, which range from mild damage to complete kidney failure. The stages are determined based on declining kidney function and glomerular filtration rate (GFR). GFR measures the kidneys’ ability to filter waste from the body, with a normal range of 90 to 120 mL/min/1.73 m2.

Symptoms and complications increase as the stages progress.

Stage I (normal or minimal loss of kidney function)

Kidney damage is very mild, with GFR of 90 mL/min/1.73 m2 or above. No symptoms are present, but tests may indicate kidney damage.

Stage II (mild or moderately reduced kidney function)

Kidney damage is mild, with GFR between 60 and 89 mL/min/1.73 m2. No symptoms are present, but tests may indicate kidney damage.

Stage III (moderate to severe loss of kidney function)

Kidneys do not function as efficiently as they should, with GFR between 30 and 59 mL/min/1.73 m2. Symptoms may include fatigue, swelling, back pain, urination issues, and high blood pressure.

Stage III kidney disease is divided into IIIA and IIIB.

• Stage IIIA (early) refers to GFR between 45 and 59 mL/min/1.73 m2.
• Stage IIIB (late) refers to GFR between 30 and 44 mL/min/1.73 m2.

Stage IV (severely reduced kidney function)

Kidneys are severely damaged, with GFR between 15 and 29 mL/min/1.73 m2. Symptoms may worsen, leading to complications such as anemia, high blood pressure, and bone disease.

Stage V (kidney failure or end-stage renal disease or ESRD)

Kidneys are close to or in complete failure, with GFR less than 15 mL/min/1.73 m2. Symptoms of kidney failure become evident and include loss of appetite, vomiting, muscle cramps, swelling, urination changes, breathing trouble, and itchy skin. Dialysis or a kidney transplant is necessary for survival.

By clicking Submit, I agree to the MedicineNet’s Terms & Conditions & Privacy Policy and understand that I may opt out of MedicineNet’s subscriptions at any time.

Medscape Medical Reference

National Kidney Foundation

National Kidney Foundation