Q: How does acute tubular necrosis affect FENa?

ATN damages the tubular epithelium, impairing sodium reabsorption. This results in a FENa >2–3%. However, non-oliguric ATN or early ATN may show FENa in the indeterminate range.

Question 1

When should I use FEUrea instead of FENa?

Accepted Answer

FEUrea is preferred when the patient is on diuretic therapy, as urea handling is less affected by diuretics than sodium. It is also more reliable in early AKI and cardiorenal syndrome.

Question 2

Can FENa differentiate between prerenal AKI and glomerulonephritis?

Accepted Answer

No. Glomerulonephritis typically presents with low FENa (<1%) because tubular function is initially intact. The clinical context, urinalysis (dysmorphic RBCs, casts), and serology are needed to differentiate GN from prerenal causes.

Question 3

How does acute tubular necrosis affect FENa?

Accepted Answer

ATN damages the tubular epithelium, impairing sodium reabsorption. This results in a FENa >2–3%. However, non-oliguric ATN or early ATN may show FENa in the indeterminate range.

Question 4

What is the role of FENa in contrast-induced AKI?

Accepted Answer

FENa is less useful in contrast-induced AKI, where tubular function is often preserved and FENa may remain low (<1%). Alternative biomarkers (NGAL, KIM-1) are being investigated for this indication.