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Calculator · Pre-renal or intrinsic — when the urine can tell you
Fractional excretion of sodium and urea
A low fractional excretion means the kidney is holding on to sodium, which is what an underperfused kidney does. FeUrea is the one that still works on diuretics, which matters because most inpatients with an AKI are already on furosemide by the time anyone…
Before you use it
Rarely changes management on its own, and is invalid in several common situations: any loop diuretic within about 24 hours (use FeUrea), CKD, contrast nephropathy, rhabdomyolysis and early glomerulonephritis can all give a low FeNa despite intrinsic injury. Obstruction is not excluded by any of this — scan the bladder.
Source: Carvounis et al, Kidney Int 2002 / UKKA AKI guidance
Checked, and shown
Every threshold on this page was checked against its primary source by a practising doctor. Here is what that involved, and what it found.