What is high BUN in blood test?
High BUN (blood urea nitrogen) levels above 20 mg/dL indicate your kidneys may not be filtering waste properly, often due to dehydration, high protein intake, or kidney issues. While concerning, BUN should be evaluated alongside other markers like creatinine for accurate assessment.
Understanding BUN and Its Role in Your Body
Blood urea nitrogen (BUN) is a waste product created when your liver breaks down proteins from food or muscle tissue. This nitrogen-containing compound travels through your bloodstream to your kidneys, which filter it out and excrete it through urine. BUN testing provides valuable insights into how well your kidneys are functioning and can reveal important information about your overall metabolic health.
When doctors order a BUN test, they're essentially checking how efficiently your body processes and eliminates protein waste. This simple blood test serves as a window into your kidney function, hydration status, and protein metabolism. Understanding your BUN levels can help identify potential health issues before they become serious problems.
Normal vs. High BUN Levels
Normal BUN levels typically range from 7 to 20 milligrams per deciliter (mg/dL), though this can vary slightly between laboratories. Levels above 20 mg/dL are generally considered elevated, while levels exceeding 50 mg/dL indicate severe elevation requiring immediate medical attention. However, interpreting BUN results isn't always straightforward, as various factors can influence these numbers.
Age plays a role in BUN levels, with older adults often having slightly higher baseline values. Children typically have lower BUN levels, ranging from 5 to 18 mg/dL. Athletes and individuals with higher muscle mass may also have slightly elevated BUN due to increased protein turnover. Understanding these variations helps provide context when evaluating your results.
The BUN-to-Creatinine Ratio
Healthcare providers often look at BUN alongside creatinine levels to get a more complete picture of kidney function. The BUN-to-creatinine ratio normally falls between 10:1 and 20:1. A ratio higher than 20:1 might suggest dehydration or increased protein breakdown, while a lower ratio could indicate liver disease or malnutrition. This ratio helps distinguish between different causes of elevated BUN.
Common Causes of High BUN
Elevated BUN levels can result from various conditions affecting either the production of urea or its elimination from the body. Understanding these causes helps determine the appropriate response to abnormal test results.
Kidney-Related Causes
Kidney dysfunction remains the most concerning cause of elevated BUN. When kidneys can't filter waste effectively, BUN accumulates in the blood. Conditions that can impair kidney function include:
- Chronic kidney disease (CKD)
- Acute kidney injury
- Glomerulonephritis (kidney inflammation)
- Kidney stones blocking urine flow
- Polycystic kidney disease
Non-Kidney Causes
Many factors unrelated to kidney disease can elevate BUN levels. Dehydration concentrates BUN in the blood, making it one of the most common causes of mild elevation. High-protein diets or supplements can increase urea production, as can certain medications like corticosteroids or tetracycline antibiotics.
Other non-kidney causes include gastrointestinal bleeding (where blood proteins are digested and converted to urea), severe burns or trauma (causing muscle breakdown), and heart failure (reducing blood flow to the kidneys). Fever, infection, and extreme exercise can also temporarily raise BUN levels through increased protein metabolism.
Symptoms Associated with High BUN
Mildly elevated BUN often causes no noticeable symptoms. However, as levels rise, particularly above 40-50 mg/dL, various symptoms may develop. These symptoms often reflect the underlying cause rather than the elevated BUN itself.
Common symptoms associated with high BUN include:
- Fatigue and weakness
- Nausea and vomiting
- Loss of appetite
- Confusion or difficulty concentrating
- Metallic taste in mouth
- Swelling in legs, ankles, or feet
- Changes in urination frequency or volume
- Shortness of breath
- Itchy skin
When BUN levels become severely elevated (a condition called uremia), more serious symptoms can develop, including muscle cramps, seizures, and altered mental status. These symptoms require immediate medical attention.
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Testing and Monitoring BUN Levels
BUN testing typically occurs as part of a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP). These panels provide a broader view of your metabolic health, including electrolytes, glucose, and other kidney function markers. Regular monitoring helps track kidney health over time and can catch problems early when they're most treatable.
When to Get Tested
Your doctor may recommend BUN testing if you have risk factors for kidney disease, such as diabetes, high blood pressure, or a family history of kidney problems. Testing is also appropriate if you're experiencing symptoms like persistent fatigue, changes in urination, or unexplained swelling. Annual testing as part of routine health screening helps establish your baseline and detect changes over time.
Interpreting Your Results
BUN results should never be interpreted in isolation. Your healthcare provider will consider your complete clinical picture, including other lab values, symptoms, medications, and medical history. A single elevated reading doesn't necessarily indicate a serious problem, especially if other kidney function markers like creatinine and eGFR are normal.
Natural Ways to Lower High BUN
If your BUN is mildly elevated due to lifestyle factors, several natural approaches can help bring levels back to normal. These strategies focus on supporting kidney function and optimizing protein metabolism.
Hydration and Diet
Proper hydration remains the simplest and most effective way to lower BUN levels. Aim for at least 8-10 glasses of water daily, more if you're active or live in a hot climate. Adequate hydration helps kidneys flush out waste products more efficiently.
Dietary modifications can also help. Consider moderating protein intake if you consume very high amounts, as excess protein increases urea production. Focus on high-quality protein sources and balance them with plenty of fruits, vegetables, and whole grains. Limiting sodium intake supports kidney function by reducing the workload on these vital organs.
Lifestyle Modifications
Regular exercise improves circulation and kidney function, but avoid extreme workouts that can temporarily spike BUN through muscle breakdown. Managing stress through meditation, yoga, or other relaxation techniques can also support overall metabolic health. If you take medications that might affect BUN levels, discuss alternatives with your healthcare provider.
When High BUN Requires Medical Attention
While mild BUN elevation often resolves with simple lifestyle changes, certain situations require prompt medical evaluation. Seek immediate care if you experience severe symptoms like confusion, chest pain, difficulty breathing, or significant swelling. BUN levels above 50 mg/dL, especially with elevated creatinine, warrant urgent assessment.
Persistent elevation despite lifestyle modifications also needs investigation. Your doctor may order additional tests like urine analysis, kidney ultrasound, or specialized kidney function tests to determine the underlying cause. Early detection and treatment of kidney disease can prevent progression and preserve kidney function.
If you have existing health conditions like diabetes or hypertension, maintaining good control of these diseases helps protect kidney function. Regular monitoring through comprehensive blood testing allows you to track your progress and adjust your health strategy as needed. For a complete analysis of your existing blood test results, including BUN and other kidney markers, you can use SiPhox Health's free upload service to get personalized insights and recommendations.
Taking Control of Your Kidney Health
Understanding your BUN levels empowers you to take proactive steps toward better kidney health. While a high BUN reading can be concerning, it's often reversible with appropriate interventions. Focus on maintaining good hydration, eating a balanced diet, exercising regularly, and monitoring your levels through periodic testing.
Remember that BUN is just one piece of the kidney health puzzle. Comprehensive testing that includes creatinine, eGFR, and other metabolic markers provides the most accurate assessment of your kidney function. By staying informed and working with your healthcare team, you can maintain optimal kidney health and catch potential problems before they become serious.
References
- Hosten AO. BUN and Creatinine. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 193.[PubMed]
- Gowda S, Desai PB, Kulkarni SS, Hull VV, Math AA, Vernekar SN. Markers of renal function tests. N Am J Med Sci. 2010;2(4):170-173.[PubMed]
- Higgins C. Urea and the clinical value of measuring blood urea concentration. Acutecaretesting.org. 2016 Aug.[Link]
- Salazar JH. Overview of Urea and Creatinine. Lab Med. 2014;45(1):e19-e20.[DOI]
- National Kidney Foundation. Understanding Lab Values. National Kidney Foundation. 2023.[Link]
- Baum N, Dichoso CC, Carlton CE. Blood urea nitrogen and serum creatinine. Physiology and interpretations. Urology. 1975;5(5):583-588.[PubMed]
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