Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (758 page)

   Interpretation

Increased Ratio (
>
10:1) with Normal Creatinine In

   Prerenal azotemia (e.g., heart failure, salt depletion, dehydration, blood loss) due to decreased GFR

   Catabolic states with increased tissue breakdown

   GI hemorrhage; a ratio ≥36 is reported to distinguish upper from lower GI hemorrhage in patients with negative gastric aspirate.

   High protein intake

   Impaired renal function plus

   Excess protein intake or production or tissue breakdown (e.g., GI bleeding, thyrotoxicosis, infection, Cushing syndrome, high-protein diet, surgery, burns, cachexia, high fever)

   Urine reabsorption (e.g., ureterocolostomy)

   Patients with reduced muscle mass (subnormal creatinine production)

   Certain drugs (e.g., tetracycline, glucocorticoids)

   Selective increase in plasma urea (diuretic-induced azotemia) during use of loop diuretics

Increased Ratio (
>
10:1) with Elevated Creatinine In

   Postrenal azotemia (BUN rises disproportionately more than creatinine) (e.g., obstructive uropathy)

   Prerenal azotemia superimposed on renal disease