BUN/Creatinine Ratio

Ratio that helps assess kidney function

16/22Providers
Kidney FunctionCategory
10:1 to 20:1Reference
Widely Available

16 of 22 providers

Category

Kidney Function

Reference Range

10:1 to 20:1

What is BUN/Creatinine Ratio?

The BUN/Creatinine Ratio is a calculated value that compares the level of blood urea nitrogen (BUN) to creatinine in your blood. This simple ratio provides valuable diagnostic information by helping distinguish between different causes of elevated kidney markers. The ratio is calculated by dividing BUN by creatinine (both in mg/dL), with a normal range typically between 10:1 and 20:1.

The ratio is diagnostically powerful because BUN and creatinine respond differently to various conditions. Dehydration, heart failure, and GI bleeding preferentially increase BUN (raising the ratio above 20), while intrinsic kidney disease tends to increase both proportionally (ratio remains 10-20). Low ratios (<10) can indicate liver disease, malnutrition, or conditions affecting urea production.

The BUN/creatinine ratio essentially separates "pre-renal"azotemia (elevated BUN/creatinine due to factors before the kidney like dehydration or bleeding) from "renal"azotemia (both elevated due to kidney disease itself). This distinction is clinically crucial as pre-renal causes are often quickly reversible with fluids or treating the underlying cause, while renal causes require different management and may be irreversible.

Why the BUN/Creatinine Ratio Differentiates Kidney Problems

  • Pre-renal vs renal distinction:Ratio >20 suggests pre-renal (dehydration, heart failure, shock) where kidneys are structurally normal. Ratio 10-20 suggests intrinsic kidney disease
  • GI bleeding detection:Ratio >30 is highly suggestive of upper GI bleeding (blood digested provides protein load that increases BUN disproportionately)
  • Hydration assessment:Elevated ratio often indicates dehydration—simple, quick screening before more invasive tests
  • Guides treatment:Pre-renal azotemia responds to fluids;intrinsic renal disease requires different management
  • Low ratio significance:<10 can indicate liver disease (reduced urea synthesis), malnutrition, or SIADH
  • Cost-effective:No additional testing needed—calculated from routine metabolic panel

Optimal vs Standard Ranges

Normal Ratio
10:1 to 20:1▼
  • Normal balance between BUN and creatinine, indicating adequate hydration, normal protein metabolism, and proportional kidney function
  • No evidence of pre-renal azotemia, GI bleeding, or liver dysfunction
  • Both BUN and creatinine are being produced and cleared appropriately
Borderline High Ratio
20:1 to 25:1▼
  • Suggests mild pre-renal azotemia
  • Common causes:mild dehydration, early heart failure, high protein diet, increased protein catabolism (fever, steroids)
  • If BUN/creatinine both normal, likely benign
  • If both elevated, rehydrate and retest
  • Usually resolves with increased fluid intake
  • If persistent, investigate further for heart failure or protein metabolism issues
High Ratio (Pre-renal Azotemia)
25:1 to 35:1▼
  • Indicates significant pre-renal azotemia
  • BUN elevated out of proportion to creatinine
  • Causes:moderate to severe dehydration, heart failure with reduced kidney perfusion, upper GI bleeding (ratio often >30), shock states
  • Check volume status and hydration
  • IV fluids if dehydrated
  • Evaluate for GI bleeding (melena, hematemesis)
  • Assess cardiac function if heart failure suspected
  • Should improve rapidly with treatment of underlying cause
Very High Ratio
>35:1▼
  • Highly suggestive of upper GI bleeding (ratio often >40 in significant bleeds) or severe volume depletion
  • Requires urgent evaluation
  • Look for signs of bleeding:melena (black tarry stools), hematemesis, orthostatic hypotension, tachycardia
  • Consider upper endoscopy if GI bleeding suspected
  • If no bleeding, evaluate for severe dehydration, shock, or extremely high protein load
  • Rarely seen in catabolic states or steroid use
Standard lab range: 10:1 to 20:1
Sources:PMID:35166184, PMID:29497527, PMID:31379211

Scientific Evidence

BUN/Creatinine Ratio for Pre-renal Azotemia

A BUN/creatinine ratio >20 has 70-85% sensitivity and 60-75% specificity for diagnosing pre-renal azotemia versus intrinsic renal disease. Pre-renal states cause preferential BUN retention due to increased tubular urea reabsorption when kidney perfusion is reduced. This simple calculation helps distinguish reversible causes (dehydration, heart failure) from intrinsic kidney damage without additional testing.

Source:Shemesh O, et al. Limitations of creatinine as a filtration marker in glomerulopathic patients. Kidney Int. 1985;28(5):830-838. (PubMed)

GI Bleeding and Elevated BUN

Upper GI bleeding characteristically elevates BUN (often >40 mg/dL) with BUN/creatinine ratio typically >30-36. Blood in the GI tract is digested, absorbed as amino acids, and converted to urea in the liver—essentially a large protein meal. The degree of BUN elevation correlates with volume of bleeding. Lower GI bleeding causes less BUN elevation as blood passes through intestines too rapidly for significant absorption.

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

Heart Failure and Cardiorenal Syndrome

Elevated BUN/creatinine ratio is common in acute decompensated heart failure, reflecting reduced renal perfusion (pre-renal azotemia). BUN >43 mg/dL with ratio >20 predicts worse outcomes in heart failure, independent of creatinine. Aggressive diuresis may temporarily worsen the ratio but improves long-term outcomes by reducing congestion. The ratio helps distinguish true worsening kidney function from pre-renal physiology.

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.

Limitations of BUN/Creatinine Ratio

While useful, the BUN/creatinine ratio has limitations. It can be falsely elevated by high protein intake, corticosteroids, or tetracyclines, and falsely low in liver disease or malnutrition. The ratio is most reliable when interpreted in clinical context with assessment of volume status, protein intake, and liver function. It should guide—not replace—clinical judgment in diagnosing kidney dysfunction.

Source:Bagshaw SM, et al. Prognosis for long-term survival and renal recovery in critically ill patients with severe acute renal failure:a population-based study. Crit Care. 2005;9(6):R700-R709.

Low BUN/Creatinine Ratio in Liver Disease

Severe liver disease (cirrhosis, acute liver failure) impairs hepatic conversion of ammonia to urea, causing low BUN with relatively preserved creatinine, yielding ratio <10. This pattern helps distinguish hepatorenal syndrome (both BUN and creatinine elevated with normal ratio) from pure liver dysfunction. Very low BUN (<5 mg/dL) with low ratio strongly suggests impaired hepatic urea synthesis.

Source:Ginès P, et al. Management of cirrhosis and ascites. N Engl J Med. 2004;350(16):1646-1654.

Which Providers Test BUN/Creatinine Ratio?

Superpower
Included in panel
Blueprint
Included in panel
Mito Health
Included in panel
WHOOP
Included in panel
Function
Included in panel
Marek Base
Included in panel
Marek Comp.
Included in panel
Marek Complete
Included in panel
Marek Exec.
Included in panel
Empirical Health
Included in panel
Oura
Included in panel
SiPhox Health
Included in panel
Healthspan
Included in panel
Hims Adv.
Included in panel
Vitality Std
Included in panel
Vitality Elite
Included in panel

Full Provider Comparison

ProviderIncludesAnnual CostBiomarkers
SuperpowerSuperpower✓$199100+ (150 with ratios)
WHOOP Advanced LabsWHOOP Advanced Labs✓$34965
Labcorp OnDemandLabcorp OnDemand—$39830+
Life ExtensionLife Extension—$48640+
EverlywellEverlywell—$444288
Mito HealthMito Health✓$349100+
InsideTrackerInsideTracker—$76154
Function HealthFunction Health✓$365160+
Marek Health BaseMarek Health Base✓$25065
Marek Health ComprehensiveMarek Health Comprehensive✓$49570+
Marek Health CompleteMarek Health Complete✓$895100+
Marek Health ExecutiveMarek Health Executive✓$1950150+
BlueprintBlueprint✓$37580+
Quest HealthQuest Health—$Varies75+
Empirical HealthEmpirical Health✓$190100+
Oura Health PanelsOura Health Panels✓$9950
SiPhox HealthSiPhox Health✓$12460
Hims Labs BaseHims Labs Base—$19950
Hims Labs AdvancedHims Labs Advanced✓$499120+
HealthspanHealthspan✓$418870-80+
Vitality Blueprint StandardVitality Blueprint Standard✓$37585
Vitality Blueprint EliteVitality Blueprint Elite✓$700128

Related Biomarkers

Other biomarkers in the Kidney Function category:

Creatinine BUN (Blood Urea Nitrogen) eGFR (Estimated Glomerular Filtration Rate) Cystatin C Albumin/Globulin Ratio (A/G)

Frequently Asked Questions

What is BUN/Creatinine Ratio?

Ratio that helps assess kidney function

What is the optimal range for BUN/Creatinine Ratio?

The standard reference range for BUN/Creatinine Ratio is 10:1 to 20:1. Optimal ranges may differ based on individual health goals and expert recommendations.

Which blood test providers include BUN/Creatinine Ratio?

16 out of 22 blood testing providers include BUN/Creatinine Ratio in their panels. This biomarker is widely available across major providers.

What category does BUN/Creatinine Ratio fall under?

BUN/Creatinine Ratio is categorized under Kidney Function. This category includes biomarkers that help assess related aspects of health and wellness.

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.

Last reviewed:2026-02-20