Fena
Calculator

FENa estimates the percentage of filtered sodium that the kidneys actually excrete in urine, calculated by comparing sodium and creatinine concentrations in both blood and urine simultaneously. It's primarily used to help distinguish between different causes of acute kidney injury.

A low FENa (typically below 1%) suggests the kidneys are appropriately conserving sodium in response to reduced blood flow (a prerenal cause, such as dehydration), while a higher FENa (above 2%) suggests the kidney tubules themselves are damaged and can't reabsorb sodium normally (intrinsic kidney injury). This distinction directly affects how the underlying problem is treated.

FENa compares how concentrated sodium and creatinine are in the urine relative to the blood, since this ratio reflects how much filtered sodium is being reabsorbed versus excreted. Without paired blood and urine values taken close together in time, the calculation isn't meaningful.

No, diuretics directly interfere with sodium reabsorption in the kidneys, which can artificially raise FENa regardless of the true underlying cause of kidney injury. In these patients, a related test called fractional excretion of urea (FEUrea) is often used instead, since it's less affected by diuretic use.

No, FENa is a specialized clinical tool that requires simultaneous lab values and interpretation within a broader clinical context by a healthcare provider. This calculator is intended for reference and educational purposes only.