Fractional excretion of sodium in acute kidney injury
Calculates the fractional excretion of sodium, the proportion of filtered sodium that appears in the urine. It helps separate a prerenal picture, where sodium is avidly reabsorbed, from intrinsic tubular injury, where it is not.
No. Diuretics increase sodium excretion independent of volume status and invalidate the test. Fractional excretion of urea is preferred in that setting.
A low fractional excretion indicates preserved tubular sodium handling and points towards a prerenal cause; the app states the interpretation band for the value entered.
It is harder to interpret. Preterm infants have immature tubular sodium handling and physiologically higher fractional sodium excretion.
Chronic kidney disease, obstruction and salt-wasting states can all raise it, so it should be read alongside the clinical picture.