BUN Creatinine Ratio
Calculate your BUN-to-creatinine ratio from blood urea nitrogen and serum creatinine levels. Free kidney assessment tool with ratio interpretation, charts, and clinical reference ranges.
About This Calculator
The BUN creatinine ratio calculator helps assess kidney function by comparing two key blood markers: blood urea nitrogen (BUN) and serum creatinine. This ratio is a valuable diagnostic tool used by healthcare providers to distinguish between prerenal causes (reduced blood flow to the kidneys) and intrinsic renal causes (damage to kidney tissue) of acute kidney injury.
Both BUN and creatinine are waste products filtered by the kidneys, but they behave differently in the nephron. Creatinine is filtered and secreted without reabsorption, while BUN is filtered and partially reabsorbed. When kidney blood flow decreases, BUN reabsorption increases disproportionately, raising the BUN/creatinine ratio above 20:1. When kidney tissue itself is damaged, the ratio typically falls below 10:1.
The BUN creatinine ratio is calculated using the formula: BUN/Creatinine Ratio = Blood Urea Nitrogen (mg/dL) / Serum Creatinine (mg/dL). Both values must be in the same units (typically mg/dL). A normal ratio falls between 10:1 and 20:1. The normal reference range for BUN is 8–20 mg/dL, and for creatinine is 0.7–1.3 mg/dL, though these vary by age, sex, muscle mass, and laboratory standards.
Who should use this calculator? Anyone who has received a basic or comprehensive metabolic panel (BMP/CMP) and wants to understand their BUN-to-creatinine ratio. Patients with conditions affecting kidney function — including hypertension, diabetes, heart failure, chronic kidney disease, or those taking nephrotoxic medications — can monitor changes in their ratio over time.
Regional Notes: The BUN test is the standard terminology in the US and India; the UK may report it as "urea" (blood urea) instead. To convert from BUN (mg/dL) to urea (mmol/L), multiply by 0.357. In India, typical BUN reference range is 7–20 mg/dL; in the US, 8–20 mg/dL; in the UK, 2.9–7.1 mmol/L (equivalent to 8–20 mg/dL). Creatinine reference ranges: India 0.6–1.2 mg/dL (men), 0.5–1.0 mg/dL (women); US 0.7–1.3 mg/dL (men), 0.6–1.1 mg/dL (women); UK 62–115 µmol/L (men), 53–97 µmol/L (women).
Frequently Asked Questions
What is the BUN creatinine ratio?
The BUN creatinine ratio (blood urea nitrogen-to-creatinine ratio) compares the levels of urea nitrogen and creatinine in your blood. It helps healthcare providers determine whether kidney dysfunction is caused by prerenal factors (reduced blood flow to the kidneys) or intrinsic renal disease. The ratio is calculated by dividing BUN by serum creatinine, both measured in mg/dL.
What is a normal BUN creatinine ratio?
A normal BUN creatinine ratio typically falls between 10:1 and 20:1 (or 10 to 20 when expressed as a single number). Values above 20 suggest prerenal causes such as dehydration, while values below 10 may indicate intrinsic renal disease. Reference ranges can vary slightly between laboratories.
What does a high BUN creatinine ratio mean?
A BUN creatinine ratio above 20 suggests a prerenal cause, meaning reduced blood flow to the kidneys. Common causes include dehydration, hypovolemia (low blood volume), congestive heart failure, shock, severe burns, gastrointestinal bleeding, very high protein intake, or corticosteroid use. Advanced age can also elevate the ratio.
What does a low BUN creatinine ratio mean?
A BUN creatinine ratio below 10 indicates an intrinsic renal cause, meaning damage to the kidney tissue itself. Possible causes include acute tubular necrosis, liver disease, malnutrition, pregnancy, SIADH (syndrome of inappropriate antidiuretic hormone), or rhabdomyolysis. Further testing is needed to identify the specific cause.
How is the BUN creatinine ratio calculated?
The BUN creatinine ratio is calculated using the formula: BUN/Creatinine Ratio = Blood Urea Nitrogen (mg/dL) / Serum Creatinine (mg/dL). Both values are measured from a standard blood sample. The units must be the same (typically mg/dL). For example, a BUN of 15 mg/dL and creatinine of 1.0 mg/dL gives a ratio of 15.
What is the normal range for BUN and creatinine?
Normal blood urea nitrogen (BUN) levels range from 8 to 20 mg/dL (2.9–7.1 mmol/L). Normal serum creatinine levels range from 0.7 to 1.3 mg/dL (62–115 µmol/L) for most adults, though values vary by muscle mass, age, and sex. Reference ranges may differ between laboratories in India, the US, and the UK.
Can I rely on this calculator for medical diagnosis?
No. This calculator is for educational and reference purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider to interpret your lab results and BUN creatinine ratio in the context of your overall health and medical history.
What blood test includes BUN and creatinine?
BUN and creatinine are typically measured as part of a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). These tests are commonly ordered during routine health checkups, pre-surgical evaluations, or when investigating symptoms of kidney disease such as fatigue, swelling, changes in urination, or hypertension.