BUN-to-Creatinine Ratio Calculator

The Blood Urea Nitrogen-to-Creatinine (BUN/Cr) ratio is a simple calculated biomarker used to differentiate prerenal azotemia from intrinsic renal causes of acute kidney injury (AKI), and to estimate the etiology of elevated creatinine. Normal BUN/Cr ratio: 10–15. An elevated ratio (> 20) suggests prerenal azotemia (dehydration, heart failure, GI bleeding, sepsis-related hypoperfusion). A low ratio (< 10) suggests intrinsic renal causes, including acute tubular necrosis (ATN), glomerulonephritis, or SIADH. BUN/Cr interpretation is also clinically relevant for upper GI bleeding detection (protein load from blood digestion) and for identifying hypercatabolic states.