True about acute tubular necrosis: (PGI June 2007)
Ans,: D (Bloodurea: Creatinine ratio < 20) [Ref: Harrison 17th/1758,16th/1649}Renal Failure Indices Harrison I7th/i758,16th/1649Analysis of urine and blood biochemistry may be useful for distinguishing prerenal ARF from ischemic or nephrotoxic intrinsic renal ARF.# The/racfj'ona/ 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 concentration'lls 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 16th/1649, not given in H17th)Diagnostic IndexPrerenalIntrinsic Renal (i.,e., ATN)Fraction excretion of sodium<1>1Urine sodium concentration(mmol/L)<10>20Urine creatinine to plasma creatinine ratio Q>40 Q<20 QUrine urea nitrogen to plasma urea nitrogen ratio>8<3Urine specific gravity>1.020-1.010Urine osmolality (mosmol/kgH2O)>500-300Plasma BUN/creatine ratio>20<10-15Renal failure index<1>1Urinary sedimentHyaline castsMuddy brown granular casts
Urine specific gravity > 1020
Urine osmolality > 300 mosmoles/kg
Urine Na < 10 meq/L
Blood urea: creatinine ratio < 20
Renal Tubular Disease