BUN (Blood Urea Nitrogen)

Waste product from protein breakdown

20/22Providers

Kidney FunctionCategory

dehydrationReference

Widely Available

20 of 22 providers

Reference Range

dehydration

What is BUN (Blood Urea Nitrogen)?

BUN (Blood Urea Nitrogen) measures the amount of urea nitrogen in your blood. Urea is a waste product formed in your liver when protein is broken down into amino acids. The liver converts toxic ammonia (from protein breakdown) into urea, which is then carried by blood to the kidneys where it is filtered out and excreted in urine.

Unlike creatinine which is produced at a constant rate from muscle, BUN is highly variable and influenced by protein intake, hydration status, liver function, tissue breakdown (fever, steroids, GI bleeding), and kidney function. This makes BUN less specific than creatinine for assessing kidney function alone, but the BUN/creatinine ratio helps differentiate between kidney disease and other causes of elevated BUN.

BUN rises in three main scenarios:pre-renal (dehydration, heart failure, bleeding—kidney function actually normal), renal (actual kidney disease with reduced filtration), and post-renal (urinary obstruction). Low BUN can indicate liver disease (reduced urea production), malnutrition, or overhydration. The pattern of BUN elevation combined with creatinine and the BUN/creatinine ratio provides diagnostic insight.

Why BUN Complements Creatinine for Kidney Assessment

Hydration status indicator:BUN rises with dehydration and falls with overhydration more than creatinine, making it useful for assessing volume status
Pre-renal vs renal distinction:BUN/creatinine ratio >20 suggests pre-renal azotemia (dehydration, heart failure) rather than intrinsic kidney disease
GI bleeding detection:Digested blood acts as protein load, elevating BUN disproportionately to creatinine (ratio often >30)
Protein metabolism:Reflects dietary protein intake, protein catabolism, and liver urea synthesis capacity
Medication dosing:Like creatinine, used to adjust drug dosing for kidney-cleared medications
Uremia screening:Very high BUN (>80-100 mg/dL) indicates uremic syndrome requiring dialysis consideration

Optimal vs Standard Ranges

Range Type	Level	Significance
Optimal	8-20 mg/dL	Indicates balanced protein metabolism, adequate hydration, and normal kidney function. BUN/creatinine ratio typically 10-20:1. Values in this range reflect appropriate protein intake, liver synthesis, and kidney excretion without significant tissue breakdown or dehydration.
Borderline Elevated	20-30 mg/dL	May indicate mild dehydration, high protein intake, increased protein catabolism, or early kidney dysfunction. Check BUN/creatinine ratio:if >20, suspect dehydration or GI bleeding;if 10-20, suspect kidney disease. Rule out recent high-protein meal, dehydration, or medication effects (steroids, tetracycline). Retest after hydration. If persistent with normal creatinine, likely benign.
Moderately Elevated	30-60 mg/dL	Requires investigation. If BUN/creatinine ratio >20:Likely pre-renal (dehydration, heart failure, GI bleeding). Rehydrate and recheck. If ratio 10-20:Suggests kidney disease. Check urinalysis, kidney ultrasound, consider nephrology referral. Evaluate for acute kidney injury or CKD. If ratio <10:Consider liver disease or severe malnutrition (though BUN would typically be low).
Severely Elevated (Azotemia/Uremia)	>60 mg/dL	Indicates significant kidney dysfunction, severe dehydration, or major GI bleeding. BUN >80-100 mg/dL causes uremic symptoms (nausea, confusion, pericarditis) and may require dialysis. Urgent evaluation needed. Check creatinine, electrolytes (especially potassium), urinalysis. If BUN/creatinine ratio >30, investigate GI bleeding (melena, hematemesis) or severe volume depletion. If ratio normal, indicates advanced kidney failure requiring nephrology consultation.

Standard lab range: dehydration

How to Optimize BUN (Blood Urea Nitrogen)

1. Optimize Hydration Status

Adequate fluid intake:30-35 ml/kg body weight daily (about 2-3 liters for most adults). More if exercising, hot climate, or fever

Rehydration if elevated:If BUN elevated with high BUN/creatinine ratio (>20), likely dehydration. Increase oral fluids or IV hydration if severe

Monitor urine color:Aim for pale yellow. Dark urine suggests dehydration

Electrolyte balance:Replace sodium and potassium losses if dehydration from vomiting, diarrhea, or diuretics

Avoid overhydration:Excessive fluids dilute BUN and can cause hyponatremia, especially in elderly or those with SIADH

2. Adjust Protein Intake Appropriately

Normal kidney function:0.8-1.2 g/kg protein daily is appropriate. Higher BUN from high protein diet is generally benign if kidneys healthy

Early to moderate CKD (eGFR 30-90):Moderate protein to 0.8-1.0 g/kg daily to reduce kidney workload while avoiding malnutrition

Advanced CKD (eGFR <30):Low-protein diet 0.6-0.8 g/kg daily reduces BUN, delays dialysis, and improves uremic symptoms. Requires dietitian supervision

Avoid excessive protein:High-protein diets (>2 g/kg) in those with kidney disease accelerate decline

Vegetarian protein:Plant proteins may be gentler on kidneys than animal protein in CKD patients

3. Address Kidney Disease

If intrinsic kidney disease (BUN and creatinine both elevated, ratio 10-20):Follow CKD management—ACE inhibitors/ARBs if proteinuria, SGLT2 inhibitors, blood pressure control, glycemic control if diabetic

Treat underlying cause:Diabetes management, blood pressure control, discontinue nephrotoxic drugs, treat glomerulonephritis or obstruction

Monitor progression:Check BUN and creatinine every 3-6 months in CKD. Increasing BUN indicates worsening function

Uremia management:If BUN >80-100 with symptoms (nausea, confusion, fatigue), consider dialysis initiation

Phosphate binders and dietary restrictions:Advanced CKD requires phosphate restriction and mineral bone disorder management

4. Investigate and Treat GI Bleeding (if High BUN/Creatinine Ratio)

If BUN/creatinine ratio >30 with elevated BUN:Suspect GI bleeding. Blood in GI tract is digested, acting as large protein load

Check for bleeding:Look for melena (black tarry stools), hematemesis (vomiting blood), or occult blood in stool

Upper GI endoscopy:If suspected upper GI bleeding (ulcers, varices, gastritis, Mallory-Weiss tear)

Colonoscopy:If suspected lower GI bleeding (diverticulosis, polyps, cancer, angiodysplasia)

Stop NSAIDs/anticoagulants:These increase GI bleeding risk. PPI therapy for ulcers

Volume resuscitation:IV fluids, blood transfusion if significant blood loss

5. Optimize Liver Function (if Low BUN)

Low BUN (<5-8 mg/dL) suggests reduced hepatic urea synthesis or severe malnutrition

Liver disease evaluation:Check ALT, AST, bilirubin, albumin, PT/INR. Low BUN with abnormal liver enzymes suggests cirrhosis or acute liver failure

Nutritional support:If malnourished, increase protein to 1.0-1.5 g/kg daily, ensure adequate calories, consider nutritional supplements

Avoid hepatotoxins:Eliminate alcohol, minimize acetaminophen, review all medications

BCAA supplementation:In cirrhosis with low albumin, branched-chain amino acids (12-25g daily) support protein synthesis

Symptoms of Abnormal BUN (Blood Urea Nitrogen)

Low BUN (Blood Urea Nitrogen)

Low BUN (<5-8 mg/dL) rarely causes symptoms directly but may indicate:
Severe liver disease:Jaundice, ascites, confusion (hepatic encephalopathy), bleeding (low clotting factors)
Malnutrition:Muscle wasting, fatigue, poor wound healing, hair loss
Overhydration:Swelling, weight gain, shortness of breath (if severe), confusion from hyponatremia

High BUN (Blood Urea Nitrogen)

Mild elevation (20-30 mg/dL):Often asymptomatic;possible fatigue, decreased appetite
Moderate elevation (30-60 mg/dL):Nausea and vomiting, fatigue and weakness, decreased appetite, mild confusion (if uremia developing)
Severe elevation/uremia (>80-100 mg/dL):Severe nausea and vomiting, metallic taste and loss of appetite, confusion and altered mental status (uremic encephalopathy), shortness of breath (fluid overload, metabolic acidosis), chest pain (uremic pericarditis—medical emergency), itching (uremic pruritus), muscle cramps, hiccups (persistent)
GI bleeding symptoms:Black tarry stools (melena), vomiting blood, lightheadedness from blood loss

Causes of Abnormal BUN (Blood Urea Nitrogen)

Low Levels

Liver disease:Cirrhosis, acute hepatic failure—reduced urea synthesis from ammonia
Severe malnutrition:Inadequate protein intake, anorexia, eating disorders, malabsorption
Overhydration:Excessive IV fluids, SIADH (syndrome of inappropriate ADH secretion), compulsive water drinking
Pregnancy:Increased blood volume and GFR dilute BUN and increase excretion
Low-protein diet:Vegan/vegetarian diets, protein-restricted diet for CKD (though unlikely to cause very low BUN)

High Levels

Pre-renal causes (kidneys normal, BUN/creatinine ratio >20):Dehydration/volume depletion, heart failure (reduced kidney perfusion), shock or hypotension, GI bleeding (blood digested provides protein load), high-protein diet or supplements, increased protein catabolism (fever, infection, burns, steroids)
Renal causes (intrinsic kidney disease, ratio 10-20):Acute kidney injury (drugs, contrast, sepsis, rhabdomyolysis), Chronic kidney disease (diabetes, hypertension, glomerulonephritis), Glomerulonephritis or interstitial nephritis
Post-renal causes (obstruction, ratio variable):Kidney stones, enlarged prostate (BPH), bladder outlet obstruction, tumors compressing ureters
Medications:Corticosteroids (increase protein breakdown), tetracycline (reduce protein synthesis, increasing amino acid breakdown), diuretics (cause dehydration)

When to Retest

If borderline elevated (20-30 mg/dL):Retest after proper hydration in 1-2 weeks with BUN/creatinine ratio. If normalizes, was likely dehydration or high protein intake
If moderately elevated (30-60 mg/dL):Retest within 3-7 days with creatinine, electrolytes, urinalysis. If ratio >20, focus on hydration and GI bleeding evaluation. If ratio 10-20, evaluate for kidney disease
If severely elevated (>60 mg/dL):Urgent evaluation. Check daily until stable or improving. Monitor potassium and acid-base status. Consider nephrology consultation if BUN >80 mg/dL or rising rapidly
After treatment:If treated for dehydration, GI bleeding, or obstruction, retest in 2-3 days to confirm improvement
In CKD:Check BUN with creatinine every 3-6 months depending on stage. Increasing BUN/creatinine ratio may indicate dehydration or increased catabolism
Annual screening:Healthy adults should have BUN checked every 1-2 years as part of routine metabolic panel

Scientific Evidence

BUN/Creatinine Ratio for Pre-renal Azotemia

BUN/creatinine ratio >20 has 70-85% sensitivity for diagnosing pre-renal azotemia (dehydration, heart failure, hypoperfusion) versus intrinsic renal disease. In pre-renal states, kidneys increase urea reabsorption disproportionately to creatinine, raising the ratio. This simple calculation helps distinguish reversible causes (respond to fluids) from intrinsic kidney damage. Ratio >30 strongly suggests GI bleeding.

Source:Dossetor JB. Creatininemia versus uremia. The relative significance of blood urea nitrogen and serum creatinine concentrations in azotemia. Ann Intern Med. 1966;65(6):1287-1299.

BUN as Mortality Predictor in Heart Failure

Elevated BUN is a strong independent predictor of mortality in heart failure patients, even more predictive than creatinine. BUN >43 mg/dL is associated with 2-3x higher mortality risk. Elevated BUN in heart failure reflects neurohormonal activation, reduced renal perfusion, and increased protein catabolism—all markers of disease severity.

Source:Aronson D, et al. Serum blood urea nitrogen and long-term mortality in acute ST-elevation myocardial infarction. Int J Cardiol. 2008;127(3):380-385.

GI Bleeding Detection via BUN

Upper GI bleeding causes BUN elevation (typically >40 mg/dL) with BUN/creatinine ratio often >30-36 due to digestion and absorption of blood proteins in small intestine. This pattern helps identify occult GI bleeding before hemoglobin drops significantly. Lower GI bleeding (colon) causes less BUN elevation as blood passes through faster with less digestion.

Source:Srygley FD, et al. Does this patient have a severe upper gastrointestinal bleed? JAMA. 2012;307(10):1072-1079.

Low-Protein Diet Effects on BUN in CKD

Protein restriction to 0.6-0.8 g/kg/day in CKD patients significantly reduces BUN, uremic symptoms, and may delay dialysis initiation by 6-12 months. However, overly restrictive protein (<0.6 g/kg) risks malnutrition. The MDRD study showed protein restriction slowed GFR decline and improved uremia, though adherence was challenging. Dietitian supervision essential.

Source:Levey AS, et al. Effects of dietary protein restriction on the progression of advanced renal disease in the Modification of Diet in Renal Disease Study. Am J Kidney Dis. 1996;27(5):652-663.

Uremic Syndrome and Dialysis Initiation

Uremic syndrome typically manifests when BUN exceeds 80-100 mg/dL, though symptoms vary by individual and chronicity. Classic uremic symptoms (nausea, confusion, pericarditis, bleeding) indicate need for dialysis initiation. However, early dialysis (based solely on eGFR <10-15 without symptoms) does not improve outcomes compared to symptom-driven initiation. Dialysis decisions should incorporate symptoms, not just BUN/creatinine levels.

Source:Cooper BA, et al. A randomized, controlled trial of early versus late initiation of dialysis. N Engl J Med. 2010;363(7):609-619.

Which Providers Test BUN (Blood Urea Nitrogen)?

Full Provider Comparison

Provider	Includes	Annual Cost	Biomarkers
Superpower	✓	$199	100+ (150 with ratios)
WHOOP Advanced Labs	✓	$349	65
Labcorp OnDemand	✓	$398	30+
Life Extension	✓	$486	40+
Everlywell	✓	$468	83
Mito Health	✓	$349	100+
InsideTracker	—	$680	54
Function Health	✓	$365	100+
Marek Health Base	✓	$250	65
Marek Health Comprehensive	✓	$495	70+
Marek Health Complete	✓	$895	100+
Marek Health Executive	✓	$1950	150+
Blueprint	—	$399	100+
Quest Health	—	$Varies	75+
Empirical Health	✓	$190	100+
Oura Health Panels	✓	$99	50
SiPhox Health	✓	$125	60
Hims Labs Base	✓	$199	50
Hims Labs Advanced	✓	$499	120+
Healthspan	✓	$4188	80+
Vitality Blueprint Standard	✓	$375	85
Vitality Blueprint Elite	✓	$700	129

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Frequently Asked Questions

What does BUN (Blood Urea Nitrogen) test for?

BUN (Blood Urea Nitrogen) is a kidney function biomarker. Waste product from protein breakdown The normal reference range is dehydration.

Which providers include BUN (Blood Urea Nitrogen)?

20 of 22 providers include this test:Superpower, Blueprint, Mito Health, WHOOP and others.

How often should I test BUN (Blood Urea Nitrogen)?

For most people, testing 2-4 times per year is recommended to establish baseline levels and track trends. Consult your healthcare provider for personalized recommendations.

What is the optimal range?

The standard reference range is dehydration. Many functional medicine practitioners recommend tighter optimal ranges for peak health. Your ideal range may vary based on age, sex, and health goals.

Why is BUN (Blood Urea Nitrogen) important?

Indicates kidney function and hydration status. Elevated in kidney disease

Medical Disclaimer

This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.