RENAL PHYSIOLOGY-FRACTIONAL EXCRETION OF SODIUM

SUMMARY

1. The fractional excretion of sodium (FE_Na) is the ratio of excreted Na⁺ to the total filtered load of Na⁺.

2. It is used to differentiate prerenal azotemia (FE_Na < I%, high levels of nitrogen-containing compounds such as creatinine and urea) from acute tubular necrosis (FE_Na > 2%, ATN).

3. Other causes of AKI with FE_Na < I% include: contrast­ induced ATN, cardio-renal syndrome, hepato-renal syndrome, non-oliguric ATN, pigment nephropathy & acute glomerulonephritis.

Reference(s)

Wilkinson, I. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press.
Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited. https://www.tg.org.au [Accessed 2021].