Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (751 page)

   Interpretation

Increased In

   Impaired kidney function: A BUN of 50–150 mg/dL implies serious impairment of renal function. A markedly increased BUN (150–250 mg/dL) is virtually conclusive evidence of severely impaired glomerular function.

   Prerenal azotemia—any cause of reduced renal blood flow:

   CHF

   Salt and water depletion (vomiting, diarrhea, diuresis, sweating)

   Shock

   Postrenal azotemia—any obstruction of urinary tract (increased BUN-to-creatinine ratio).

   Increased protein catabolism (serum creatinine remains normal):

   Hemorrhage into the GI tract

   AMI

   Stress

Decreased In

   Diuresis (e.g., with overhydration, often associated with low protein catabolism).

   Severe liver damage (e.g., drugs, poisoning, hepatitis). A low BUN of 6–8 mg/ dL is frequently associated with states of overhydration or liver disease.