Abnormal BUN-to-Creatinine Ratios

A low BUN-to-creatinine ratio can occur through decreased BUN, increased creatinine, or both. Dehydration can concentrate BUN and creatinine while reducing renal clearance capacity. Liver disease can reduce BUN independently of kidney function by disrupting urea synthesis from ammonia. Low protein intake can lower BUN by reducing urea production. Pregnancy can lower the ratio through dilution from increased blood volume and fluid retention. Congestive heart failure can raise the ratio by reducing cardiac output and renal perfusion. Severe gastrointestinal bleeds can raise BUN while reducing renal perfusion. An elevated BUN-to-creatinine ratio can reflect impaired kidney function, reduced GFR, or glomerular damage.