Nephrology · Pathway 2

Acute Kidney Injury: ATN vs Pre-Renal Uraemia

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Key points

Urine sodium: pre-renal < 20 mmol/L, ATN > 40 mmol/L
Urine osmolality: pre-renal > 500 mOsm/kg, ATN < 350 mOsm/kg
Fractional sodium excretion: pre-renal < 1%, ATN > 1%
Response to fluid challenge: pre-renal good, ATN poor
Serum urea:creatinine ratio: raised in pre-renal, normal in ATN
Pre-renal uraemia occurs because the kidneys hold on to sodium to preserve intravascular volume