Overview Disorder FeNA+% BUN:Cr UOsm UNa+ Urinalysis Prerenal azotemia < 1 % > 15 > 500 < 20 Hyaline casts Acute glomerulonephritis < 1 % > 15 > 500 < 20 RBC casts and hematuria Acute tubular necrosis > 2 % < 15 < 350 > 40 Renal tubular casts Postrenal azotemia > 2% 10-20 < 350 > 40 Normal Defined as < 400 mL per day of urine output Causes prerenal azotemia acute glomerulonephritis acute tubular necrosis postrenal azotemia Evaluation fractional excretion of Na (FENa+ %) amount of sodium that is lost in the urine compared over the amount of sodium that is filtered (Urine Na / Plasma Na) / (Urine Cr / Plasma Cr) normally < 1% with proper tubular function BUN:Creatinine ratio in the plasma > 15 indicates proper tubular function < 15 in abnormal function due to the inability to reabsorb urea from the urine urine osmolar concentration > 500 mOsm/kg indicates proper kidney concentrating function urine sodium concentration < 20 indicates proper tubular function References