The urine urea nitrogen to serum urea nitrogen ratio is used in distinction of prerenal azotemia from ATN (after exclusion of postrenal azotemia)


urine UN to serum UN ratio =

= (urine urea nitrogen in mg/dL) / (serum urea nitrogen in mg/dL)



• A ratio < 3 is seen acute tubular necrosis (acute oliguric renal failure).

• A ratio > 8 is seen with prerenal azotemia, acute obstructive renal failure and acute glomerulonephritis


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