Simple explanation of the BUN (Blood Urea Nitrogen) test. Learn what BUN measures, normal ranges, causes of high or low BUN, and how it relates to kidney function.

BUN (Blood Urea Nitrogen)

🔍 What Is BUN? 

BUN measures the amount of urea nitrogen in your blood.

Urea is a waste product that forms when your body breaks down protein from food.

Healthy kidneys remove urea from the blood and get rid of it in urine.

So:

👉 BUN is another way to see how well the kidneys are filtering waste.

🧮 Why Is BUN Tested? 

Doctors use BUN to help answer questions like:

• Are the kidneys removing waste properly?
  
  

• Could dehydration be affecting the kidneys?
  
  

• Is there a possible kidney problem?
  
  

BUN is usually checked together with other tests like creatinine and GFR.

📊 What Is a Normal BUN Level? 

Normal ranges can vary slightly by lab, but in general:

• Typical adult range: about 7 – 20 mg/dL
  
  

What is normal for you can depend on:

• your age
  
  

• how much protein you eat
  
  

• your hydration level
  
  

• your overall health
  
  

That’s why BUN is never looked at by itself.

❗ What Does a High BUN Mean? 

A higher-than-normal BUN level can happen for several reasons, including:

• dehydration
  
  

• kidney problems
  
  

• heart problems
  
  

• high-protein diets
  
  

• certain medications
  
  

• infections or illness
  
  

A high BUN does not automatically mean you have kidney disease.

Often it simply means you need more fluids.

🔽 What Does a Low BUN Mean? 

Low BUN is less common and usually not serious.

It can be seen in people who:

• eat very little protein
  
  

• are malnourished
  
  

• have certain liver conditions
  
  

• are very well hydrated
  
  

Low BUN alone is rarely a kidney problem.

🔗 How BUN Relates to Other Kidney Tests 

BUN works best when looked at together with:

• Creatinine
  
  

• GFR
  
  

• BUN/Creatinine Ratio
  
  

These tests together give a clearer picture of kidney health than any single number.

💧 Dehydration and BUN 

One of the most common causes of a high BUN is simple:

👉 Not drinking enough water

When you are dehydrated, the kidneys hold onto water, and BUN can rise even if the kidneys are otherwise healthy.

🧪 How the Test Is Done 

BUN is measured with a routine blood test.

Usually no special preparation is needed, but your doctor may suggest:

• staying well hydrated
  
  

• avoiding heavy exercise right before testing
  
  

• reviewing medications

🧭 What Usually Happens Next? 

If your BUN is higher than expected, your doctor may:

• repeat the test
  
  

• check creatinine and GFR
  
  

• ask about fluid intake
  
  

• review your medications
  
  

• order a urine test
  
  

Often the first step is simply to recheck the number.

❓ Common Questions 

Can drinking water lower BUN?
Yes. If dehydration is the cause, better hydration can quickly improve BUN levels.

Can medications raise BUN?
Yes. Some antibiotics, diuretics, and other medicines can affect BUN.

Does diet affect BUN?
Yes. Eating a lot of protein can raise BUN temporarily.

Is a slightly high BUN serious?
Not usually. Mild changes are very common and often temporary.

🚩 When to Worry 

Contact a healthcare provider if a high BUN is combined with:

• very little urine
  
  

• severe swelling
  
  

• confusion
  
  

• vomiting
  
  

• extreme fatigue
  
  

These could signal a more serious issue.

📌 Where to Go Next 

To understand related results, visit:

• Creatinine Blood Test Explained
  
  

• What Is GFR / eGFR?
  
  

• BUN/Creatinine Ratio Explained
  
  

• Urinalysis Results Explained