<prompt> True about acute tubular necrosis: PGI June 2007Urine specific gravity 1020Urine osmolality 300 mosmoleskgUrine Na 10 meqLBlood urea: creatinine ratio 20  <response>: Ans,: D Bloodurea: Creatinine ratio 20 Ref: Harrison 17th1758,16th1649Renal Failure Indices Harrison I7thi758,16th1649Analysis of urine and blood biochemistry may be useful for distinguishing prerenal ARF from ischemic or nephrotoxic intrinsic renal ARF. Theracfjona excretion of sodium FE is most useful in this regard-. The FENa relates sodium clearance to creatinine clearance. Sodium is reabsorbed avidly from glomerular filtrate in patients with prerenal ARF, in an attempt to restore intravascular volume. The FENa tends to be high in ischemic ATN but is often low in patients with sepsis-induced, pigment-induced, and some forms of nephrotoxic ATN e.g., contrast-associated 1In contrast, creatinine is not reabsorbed in either setting. Consequently, patients with prerenal ARF typically have a FEof 1.0 frequently 0.1. In patients with metabolic alkalosis, where there may be obligate losses of sodium in the urine to maintain electroneutrality, the fractional excretion of chloride FECI may be more sensitive than the FESj in detecting prerenal azotemia.The urine sodium concentrationlls a less-sensitive index for distinguishing prerenal ARF from ischemicand nephrotoxic ARF as values overlap between groups. Similarly, indices of urinary concentrating ability such as urine specific gravity, urine osmolality, urine-to-plasma urea ratio, and blood urea-to-creatinine ratio are of limited value in differential diagnosis.Many caveats apply when interpreting biochemical renal failure indices. The FEVi may be 1.0 in prerenal ARF if patients are receiving diuretics or with preexisting chronic kidney disease, certain salt-wasting syndromes, or adrenal insufficiency.Urine Diagnostic Indices in Differentiation of Prerenal versus Intrinsic Renal ARF Harrison 16th1649, not given in H17thDiagnostic IndexPrerenalIntrinsic Renal i.,e., ATNFraction excretion of sodium11Urine sodium concentrationmmolL1020Urine creatinine to plasma creatinine ratio Q40 Q20 QUrine urea nitrogen to plasma urea nitrogen ratio83Urine specific gravity1.020-1.010Urine osmolality mosmolkgH2O500-300Plasma BUNcreatine ratio2010-15Renal failure index11Urinary sedimentHyaline castsMuddy brown granular casts 