Blood Urea Nitrogen (BUN)
Blood Urea Nitrogen measures the amount of nitrogen in the blood derived from urea, the final breakdown product of protein catabolism synthesized by the hepatic ornithine cycle.
Standard vs. Optimal Reference Rangesmg/dL
Standard reference intervals represent the statistical 95% distribution of unselected commercial populations. Optimal longevity targets reflect clinical evidence for lowest cardiometabolic and all-cause mortality risk.
Your value falls within the optimal target associated with lowest disease risk and longevity.
7 - 20 mg/dL
General reference distribution across unselected commercial populations.
10 - 15 mg/dL
Concentration target associated with minimal all-cause cardiometabolic mortality.
Molecular Mechanism & Clinical Purpose
Ammonia generated by deamination of amino acids is converted to urea by hepatic mitochondria and cytosol. Urea is filtered freely at the glomerulus; 40-50% is passively reabsorbed in proximal and medullary collecting tubules.
Differential Diagnosis
Elevated Levels (BUN High)
- •Hypovolemia / Dehydration (increased proximal tubule reabsorption)
- •High dietary protein intake
- •Upper gastrointestinal bleeding
- •Renal failure
Low Levels (BUN Low)
- •Severe hepatic insufficiency (impaired urea synthesis)
- •Protein malnutrition or low-protein vegan diet
- •Syndrome of inappropriate antidiuretic hormone (SIADH)
Technical Reference & Deep Dive
Biochemistry & Enzymatic Pathways
Longevity Risk Architecture & Epidemiology
Pre-Analytical Caveats & Diagnostic Workup
Pre-Analytical Considerations:
Maintain standard hydration status prior to venipuncture; acute hypovolemia or hemoconcentration artificially elevates concentrations. Avoid heavy resistance training and high-protein meals (especially cooked red meat) for 24 hours prior if testing serum creatinine. Ensure tourniquet time does not exceed 60 seconds to avoid pseudohyperkalemia or hemoconcentration of electrolyte fractions.
Reflexive Testing Protocol:
- Simultaneous Serum Cystatin C testing to calculate composite CKD-EPI Creatinine-Cystatin C eGFR equation
- Spot Urine Albumin-to-Creatinine Ratio (uACR) to detect subclinical glomerular endothelial leak
- Renal duplex ultrasonography to assess bilateral kidney dimensions, cortical echogenicity, and resistive index
- Fractional Excretion of Sodium (FENa) and Urea (FEUrea) to differentiate prerenal azotemia from intrinsic acute kidney injury
- Serum and urine protein electrophoresis (SPEP/UPEP) if tubular injury or monoclonal gammopathy is suspected
Clinical Citations & Primary Literature (1)
- [1]Blood Urea Nitrogen as a Biomarker in Critical Illness and Longevity - American Journal of Kidney Diseases (2022). PMID: 34800615
Associated Longevity Guides & Clinical Calculators
Medicine 3.0Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate Blood Urea Nitrogen (BUN) into overall healthspan optimization.