Clinical QuickieRenal/Electrolytes
BUN/Creatinine Ratio
A clue, not a diagnosis.
Look at the Two Numbers First
BUN and creatinine are influenced by different processes.
Interpret each value, baseline and trajectory before focusing on the ratio.
A High Ratio Has Multiple Explanations
Pre-renal physiology can raise it, but so can upper GI bleeding, catabolic illness, corticosteroids or high protein load.
The ratio alone does not distinguish between these causes.
Low Creatinine Can Inflate It
Frailty, low muscle mass, amputation or cachexia can make the ratio look dramatic even when BUN is only modestly elevated.
Always interpret the ratio in the context of the patient's body composition.
Use It to Support a Story
Volume history, hemodynamics, kidney trajectory and bleeding clues are more diagnostic than a stand-alone ratio cutoff.
The ratio is most useful when it agrees with a coherent clinical story.
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