Which differentiating prerenal azotemia with ATN features oring pre-renal azotemia -: (A) Urine osmolality > 500 mosmol/kg, (B) Sodium spot excretion < 10 ml/L, (C) Plasma transferrin/Ig ratio, (D) All the above
Answer is A. The normal kidney can elaborate urine with a maximum concentration greater than 1,200 mOsm/kg in states of dehydration. A urinary osmolality (Uosm) greater than 500 mOsm/kg,, is highly suggestive of prerenal azotemia Ref Harrison20th edition pg ,299