BUN Normal Range (By Age)

Blood Urea Nitrogen Test (BUN): Normal Range by Age

The Blood Urea Nitrogen Test (BUN) is a common blood test used to help assess how well your kidneys are working. It measures the amount of urea nitrogen in your blood—a waste product made when your body breaks down protein. Healthy kidneys filter urea out of the blood and remove it through urine. When this process changes, BUN levels can rise or fall.

This guide explains normal BUN ranges by age, what affects BUN levels, and when results may matter. The goal is to inform—without causing unnecessary worry—so you can have informed conversations with your healthcare provider.

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What Is the Blood Urea Nitrogen Test (BUN)?

The Blood Urea Nitrogen Test (BUN) measures the concentration of urea nitrogen in your blood. Urea is produced in the liver and carried by the bloodstream to the kidneys for removal.

Doctors commonly order a BUN test as part of:

• A basic or comprehensive metabolic panel
• Routine health checkups
• Evaluation of kidney function
• Monitoring dehydration, infection, or chronic conditions
• Follow-up for certain medications that affect the kidneys

BUN is rarely interpreted alone. It’s typically reviewed alongside creatinine, urine tests, symptoms, and medical history.

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Why BUN Levels Change

BUN levels can change for many reasons—not all of them serious. Common influences include:

• Kidney function (filtering efficiency)
• Hydration status (dehydration can raise BUN)
• Protein intake (high-protein diets may increase BUN)
• Age
• Medications (such as diuretics or some antibiotics)
• Liver function
• Recent illness, infection, or injury

Because so many factors play a role, a single BUN value does not usually tell the whole story.

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Normal BUN Range by Age

Below are general reference ranges for the Blood Urea Nitrogen Test (BUN) by age. These ranges are based on widely accepted clinical references used in hospitals and laboratories. Keep in mind that normal ranges may vary slightly by lab.

Newborns (0–2 months)

• Normal BUN range: 3–12 mg/dL

Newborns typically have lower BUN levels due to immature kidney function and lower protein intake.

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Infants and Children (2 months–12 years)

• Normal BUN range: 5–18 mg/dL

As children grow, kidney function matures and BUN values gradually approach adult ranges.

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Adolescents (13–17 years)

• Normal BUN range: 7–20 mg/dL

Hormonal changes, growth spurts, and diet can cause mild fluctuations, but values generally resemble adult levels.

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Adults (18–59 years)

• Normal BUN range: 7–20 mg/dL

This is the most commonly cited adult reference range for the Blood Urea Nitrogen Test (BUN).

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Older Adults (60 years and older)

• Typical range: 8–23 mg/dL (may be slightly higher)

Mildly higher BUN levels can be normal with aging due to:

• Reduced kidney filtration over time
• Changes in muscle mass
• Increased likelihood of dehydration

A slightly elevated BUN in older adults does not automatically mean kidney disease.

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What Is Considered a High or Low BUN?

High BUN Levels (Above Normal Range)

Higher-than-normal BUN levels may be associated with:

• Dehydration
• Kidney disease or reduced kidney function
• Heart failure
• Severe infections
• Gastrointestinal bleeding
• High-protein diets
• Certain medications

A high BUN does not confirm a diagnosis on its own. Doctors look at trends over time and compare BUN with creatinine levels.

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Low BUN Levels (Below Normal Range)

Low BUN levels are less common and may be seen with:

• Liver disease
• Low-protein diets
• Overhydration
• Pregnancy

Low BUN values are often less concerning but still deserve context.

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BUN vs. Creatinine: Why Both Matter

The Blood Urea Nitrogen Test (BUN) is often interpreted alongside creatinine, another waste product filtered by the kidneys.

Doctors may calculate the BUN-to-creatinine ratio, which can help clarify whether changes are more likely due to:

• Dehydration
• Kidney-related causes
• Other systemic conditions

This combined view provides a clearer picture than BUN alone.

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Symptoms That May Lead to a BUN Test

Many people with abnormal BUN levels have no symptoms, especially early on. When symptoms do occur, they may include:

• Fatigue
• Swelling in legs or feet
• Changes in urination
• Nausea or poor appetite
• Confusion in severe cases

If you notice blood in your urine, this is an important symptom to take seriously. You may want to consider doing a free, online symptom check for Blood in urine to better understand what might be going on before speaking with a healthcare professional.

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How to Prepare for a Blood Urea Nitrogen Test (BUN)

Preparation is usually simple:

• You may be asked to fast for 8–12 hours if BUN is part of a larger blood panel
• Drink normal amounts of water unless told otherwise
• Tell your doctor about all medications and supplements you take

Always follow the instructions given by your healthcare provider or lab.

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Interpreting Your Results: Important Reminders

When reviewing your Blood Urea Nitrogen Test (BUN) results, keep these points in mind:

• A single abnormal value rarely tells the whole story
• Lab “normal ranges” are guides, not absolute rules
• Age, hydration, diet, and medications matter
• Trends over time are often more meaningful than one result

Avoid self-diagnosing based solely on numbers.

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When to Speak to a Doctor

You should speak to a doctor promptly if:

• Your BUN is significantly outside the normal range
• You have symptoms like swelling, shortness of breath, confusion, or very little urine
• You notice blood in your urine
• You have known kidney disease, heart disease, or liver disease
• Your results are changing quickly over time

Anything that could be serious or life-threatening deserves medical attention, even if symptoms seem mild at first.

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Key Takeaways

• The Blood Urea Nitrogen Test (BUN) helps evaluate kidney function and overall health
• Normal BUN ranges vary by age, with slightly higher values often seen in older adults
• Many factors—not just kidney disease—can affect BUN levels
• Results should always be interpreted with other tests and clinical context
• If you have concerning symptoms, including blood in urine, seek medical guidance

If you ever feel unsure about your results or symptoms, the safest step is to speak to a doctor who can review your full health picture and guide next steps.