⚠️ Educational only. LabPlain does not provide medical advice or diagnosis. Always discuss your specific results with your healthcare provider.
What this test measures
BUN stands for Blood Urea Nitrogen. It measures the amount of urea nitrogen in your blood — a waste product created when your body breaks down protein.
Your liver produces urea, and your kidneys filter it out through urine. Because of this, BUN is commonly used as a rough marker of kidney function and hydration status.
Doctors often order BUN as part of a Comprehensive Metabolic Panel (CMP) or Basic Metabolic Panel (BMP). It's usually interpreted alongside creatinine, eGFR, and electrolytes rather than by itself.
Normal reference range
Adults: 7–20 mg/dL
Reference ranges vary slightly between labs. Age, hydration status, diet, medications, and muscle mass can all affect your result.
A mildly abnormal BUN alone is often less important than the overall pattern of kidney-related tests.
💧 Hydration matters
Dehydration is one of the most common reasons for a temporary high BUN. Even not drinking enough water before a blood draw can slightly raise your result.
What your result might indicate
↑ If High
High BUN may suggest dehydration, kidney dysfunction, high protein intake, gastrointestinal bleeding, heart failure, or severe illness. Certain medications can also raise BUN.
↓ If Low
Low BUN is less common and may occur with liver disease, malnutrition, overhydration, pregnancy, or a very low-protein diet. Mildly low values are often not clinically significant.
Symptoms associated with abnormal BUN
↑ High BUN Symptoms
Fatigue or weakness
Swelling in legs or ankles
Reduced urination
Nausea or vomiting
Shortness of breath
Confusion or brain fog
Dry mouth or dehydration symptoms
High blood pressure
↓ Low BUN Symptoms
Poor appetite
Fatigue
Muscle loss
Signs of liver disease
Excessive fluid retention
Malnutrition symptoms
Weakness
Usually no symptoms if only mildly low
Common causes of abnormal BUN
What can raise BUN?
The most common cause of elevated BUN is dehydration. When your body doesn't have enough fluid, waste products become more concentrated in the blood.
Kidney disease is another major cause because damaged kidneys cannot filter urea efficiently. Other causes include high-protein diets, gastrointestinal bleeding, severe infections, heart failure, burns, shock, and certain medications like corticosteroids or tetracycline antibiotics.
What can lower BUN?
Low BUN is less common but may happen when the liver can't produce enough urea, such as in advanced liver disease. It can also occur with malnutrition, low protein intake, pregnancy, or drinking excessive amounts of water.
In many healthy people, a slightly low BUN has little or no medical significance.
Tests often ordered alongside BUN
BUN is almost always interpreted with other kidney and metabolic tests. Your doctor may also order:
Creatinine — another key kidney function marker
eGFR — estimates how well your kidneys are filtering blood
Electrolytes — sodium, potassium, chloride, and bicarbonate
Urinalysis — checks for protein, blood, or infection in urine
Comprehensive Metabolic Panel (CMP) — broader picture of liver and kidney health
What to do next
A single abnormal BUN result usually isn't enough to diagnose a medical condition. Doctors interpret BUN alongside creatinine, eGFR, symptoms, medications, hydration status, and your medical history. Mild abnormalities are common and often temporary. Only your healthcare provider can interpret your result in the context of your full health picture.
Questions to ask your doctor
01Is my BUN abnormal enough to suggest kidney problems?
02Could dehydration or diet explain this result?
03How do my creatinine and eGFR compare with my BUN?
04Could any medications or supplements affect my result?
05Should I repeat the test after improving hydration?
06Do I need further kidney testing or imaging?
Frequently asked questions
Is high BUN always kidney disease?
No. Dehydration is one of the most common causes of elevated BUN. High-protein diets, illness, medications, and temporary stress on the body can also raise it.
Can dehydration really raise BUN?
Yes. When you're dehydrated, blood becomes more concentrated, which can temporarily increase BUN levels even if your kidneys are functioning normally.
What's the difference between BUN and creatinine?
Both are waste products filtered by the kidneys, but creatinine is generally considered a more reliable marker of kidney function. Doctors often interpret the two together.
Can a high-protein diet affect BUN?
Yes. Eating large amounts of protein can increase urea production and slightly raise BUN levels, especially in people using protein supplements or bodybuilding diets.
Is low BUN dangerous?
Usually not. Mildly low BUN is often harmless. However, significantly low values can sometimes point to liver disease, malnutrition, or excessive fluid intake.