differentiation of pre-renal failure from ATN
Last reviewed 01/2018
In pre-renal acute renal failure the kidney is responding to poor renal perfusion by retaining sodium and water ( --> low urine sodium and a concentrated urine with high osmolality).
As acute tubular necrosis develops, any glomerular filtrate produced passes out as urine with progressively less and less tubular modification, so the urine composition approaches that of plasma.
| Pre-renal Acute Renal Failure | Acute Tubular Necrosis | |
| Urine osmolality | high | falls to a level similar to plasma |
| Urine:plasma osmolality ratio | >1.5 | <1.1 |
| Urine sodium | <10mmol/L | >30mmol/L |