Calculate the fractional excretion of sodium given the serum and urine sodium, and the serum and urine creatinine.

To accurately interpret FENa, patients should not have recently received diuretics. FENa is greater than 1% and usually greater than 3% with acute tubular necrosis and severe obstruction of the urinary drainage of both kidneys. It is generally less than 1% in patients with acute glomerulonephritis, hepatorenal syndrome, and states of prerenal azotemia such as congestive heart failure or dehydration. FENa may also be less than 1% with acute partial urinary tract obstruction. -- Stein JH, ed. Internal Medicine, 4th edition. Mosby-Year Book. 1994.

The equation is:

FENa =	UNa * PCr	x 100
	PNa * UCr