BUN to Creatinine Ratio Calculator

What Is the BUN to Creatinine Ratio Calculator?

The BUN to Creatinine Ratio Calculator is a free medical tool that calculates the ratio between Blood Urea Nitrogen (BUN) and Serum Creatinine from your lab results. This ratio is a valuable clinical marker used by healthcare providers to assess kidney function, evaluate hydration status, and differentiate between prerenal and intrinsic renal causes of acute kidney injury (AKI).

BUN to Creatinine Ratio Formula

The BUN:Cr ratio is calculated by dividing the blood urea nitrogen level by the serum creatinine level:

BUN:Cr Ratio = BUN (mg/dL) / Creatinine (mg/dL)

When using different units, the calculator converts automatically:

BUN: mmol/L × 2.8 = mg/dL
Creatinine: µmol/L / 88.4 = mg/dL

Normal BUN to Creatinine Ratio Range

The normal BUN:Cr ratio for adults is typically 10:1 to 20:1. Values outside this range may indicate various conditions:

Low (< 10:1): May indicate intrinsic renal issues, liver disease, malnutrition, or rhabdomyolysis.
Normal (10:1 - 20:1): Healthy kidney function with adequate hydration.
High (> 20:1): May indicate prerenal causes such as dehydration, heart failure, or GI bleeding.

How to Use This Calculator

Enter your BUN value from your lab report.
Select the correct unit (mg/dL or mmol/L).
Enter your Serum Creatinine value.
Select the correct unit (mg/dL or µmol/L).
View your BUN:Cr ratio with instant clinical interpretation.

Related Health Calculators

For a more complete picture of your kidney health, explore our GFR Calculator to estimate your glomerular filtration rate and the Creatinine Clearance Calculator for an alternative measure of kidney function. You may also find our Corrected Calcium Calculator and BMI Calculator useful for general health monitoring.

Frequently Asked Questions

What is BUN to Creatinine Ratio?

The BUN to Creatinine ratio is a blood test value calculated by dividing the blood urea nitrogen (BUN) level by the serum creatinine level. This ratio helps healthcare providers differentiate between prerenal causes (like dehydration) and intrinsic renal causes of kidney dysfunction.

What does a high BUN to Creatinine ratio mean?

A high BUN:Cr ratio (above 20:1) typically suggests prerenal azotemia, or reduced blood flow to the kidneys. Common causes include dehydration, congestive heart failure, gastrointestinal bleeding, and high protein intake.

What does a low BUN to Creatinine ratio indicate?

A low BUN:Cr ratio (below 10:1) may indicate intrinsic renal disease, liver disease, malnutrition, pregnancy, or rhabdomyolysis. In acute tubular necrosis, both BUN and creatinine rise, but creatinine rises proportionally more.

How is BUN to Creatinine ratio calculated?

The ratio is calculated by dividing the BUN value (in mg/dL) by the serum creatinine value (in mg/dL). For example, if BUN is 20 mg/dL and creatinine is 1.0 mg/dL, the ratio is 20:1.

What are normal BUN and Creatinine levels?

Normal BUN levels range from 7-20 mg/dL (2.5-7.1 mmol/L). Normal serum creatinine levels are 0.7-1.3 mg/dL (62-115 µmol/L) for men and 0.6-1.1 mg/dL (53-97 µmol/L) for women.

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