BUN/creatinine ratio
Bladder and kidney healthAlso known as: urea-to-creatinine ratio, urea creatinine ratio, BUN/Krea
The BUN/Creatinine ratio compares blood urea nitrogen (a waste product from protein metabolism) to creatinine (a waste product from muscle metabolism).
This ratio helps distinguish between different causes of abnormal kidney values — whether changes are due to dehydration, kidney disease, or other factors affecting urea production.
Reference range
Source: Ahead Health benchmark
Reference ranges may vary between labs and assays. Always interpret results with your healthcare provider.
Why this matters
An elevated ratio may indicate dehydration, high protein intake, gastrointestinal bleeding, or reduced blood flow to the kidneys (as in heart failure). A low ratio can suggest inadequate protein intake, liver disease, or overhydration. The ratio is influenced by hydration status, dietary protein, muscle mass, and kidney blood flow. Monitoring this ratio helps distinguish between different causes of abnormal kidney function and guides appropriate interventions; such as increasing fluid intake, adjusting diet, or investigating heart or digestive issues.
How this connects to other biomarkers
- BUN/Creatinine Ratio > 20 suggests an upstream (pre-renal) cause of elevated kidney waste markers — dehydration, GI bleeding, high-protein catabolism, corticosteroids.
- A ratio of 10–20 is typical of normal kidney function or chronic kidney disease at steady state.
- A ratio < 10 may reflect malnutrition (low Albumin), liver disease (impaired urea cycle), pregnancy, or severe muscle breakdown (high Total Creatine Kinase (CK) / Myoglobin with relatively spared Urea).
How often should I test BUN/creatinine ratio?
Most adults benefit from yearly reassessment of the BUN/creatinine ratio alongside urea and creatinine, as part of kidney screening.
At baseline / for screening: Once every 12 months from age 30 as part of a kidney panel. More frequently, every 3 to 6 months, if you have hypertension, type 2 diabetes, chronic kidney disease, or take medication processed through the kidneys.
When monitoring an intervention or change: Retest 2 to 4 weeks after starting a new medication that affects the kidneys (ACE inhibitor, ARB, SGLT2 inhibitor, diuretic, NSAID, certain antibiotics) to confirm stable function. After a meaningful change in blood pressure or diabetes control, retest at 3 months. Hydration on the morning of the draw can shift creatinine-based numbers, so reproduce conditions for reliable trend tracking.
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