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About BUN/Creatinine Ratio
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About BUN/Creatinine Ratio
Overview and History
The BUN/Creatinine Ratio is a derived biochemical marker calculated from two routine blood tests: blood urea nitrogen (BUN) and serum creatinine. BUN is produced in the liver as the end product of protein metabolism, while creatinine is produced by muscle turnover and cleared by the kidneys.
Clinically this ratio has been used for decades to provide context when BUN or creatinine values shift. Instead of labeling a single value, the ratio helps differentiate whether changes are driven by production (metabolism, diet, liver function), by fluid status, or by how effectively the kidneys are clearing small nitrogenous wastes.
Interpreting Highs and Lows
An elevated BUN/Creatinine Ratio may be associated with relatively higher BUN compared with creatinine — commonly seen with reduced circulating volume, increased protein intake or breakdown, or greater urea absorption from the gut. It can also reflect shifts in kidney filtration relative to urea production.
A low ratio indicates BUN is low relative to creatinine and may be associated with low protein intake, reduced hepatic urea synthesis, overhydration, or a relatively higher creatinine from greater muscle mass or other factors. Any single ratio should be interpreted together with BUN, creatinine, electrolytes, liver tests, and clinical context for an accurate pattern assessment.
Featured Test
The BUN/Creatinine Ratio is included in the Foundation Zoomer to add context to organ function and metabolic balance. It helps flag patterns related to hydration, protein metabolism, and kidney filtration, so clinicians can interpret BUN and creatinine values within an integrated, systems‑based report and prioritize targeted follow‑up.
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Mary Beth Augustine
DCN, RDN, FAND- Lead Clinical Educator
Suzanne Barker
MS, RDN, LD, CTTS, CGP- Clinical Educator
Suzette Garcia
MSc- MHNE- Clinical Educator
Brooke Mader Ganev
MS, CNS, LDN, FDN- Clinical Educator
Adair Anderson
MS, RDN, LDN- Clinical Educator
Lillie Luu Nguyen
DCN, CNS, LDN- Clinical Educator
Jason Barker
ND- Clinical Educator
Emaline Brown
ND- Clinical Educator
Dana Filatova
DCN, CNS, LDN- Clinical Educator
Jessy Dhanjal
ND- Clinical Educator
Nour Amri
MS, LDN, CNS, CKNS- Clinical Educator
