Journal of the Medical Association of Thailand Vol 93, No 12:DECEMBER 2010 (SUPPL.7) 0125-2208 93 12 2010 Dec The Fractional Excretion of Urea in the Differential Diagnosis of Prerenal Failure and Acute Tubular Necrosis in Neonates 241 EN Jaakchai Jungthirapanich Pasakorn Srithipsukho Sookkasem Khositseth Wilaiporn Techasatid Original Article To test the hypothesis that FE UN is not effected by furosemide and useful in differentiating between prerenal failureand ATN. Neonates admitted to the Department of Pediatrics, Thammasat University Hospital from August2007-May 2009 were studies prospectively for ARF which is defined as urine output < 0.5 ml/kg/hr after the 1st day and serumcreatinine > 1.5 mg/dl with normal maternal renal function. FENa and FEUN were performed on the initial time of diagnosisand were repeated on two consecutive days. Neonates with ARF were classified as prerenal failure (n = 38) and ATN (n = 5). The prerenal failure neonates weredivided into two groups: those prerenal failure without furosemide (n = 27), those prerenal failure with furosemide (n = 11).The FENa at the initial time of diagnosis and the two consecutive days in prerenal failure neonates (0.33 + 0.57, 10.1 + 2.73,0.8 + 1.32%, respectively) were lower than ATN neonates (4.74 + 6.12, 5.05 + 4.03, 3.98 + 2.47%, respectively) significantly.Both FENa and FE UN were no statistical difference between the two prerenal failure groups and ATN neonates. A FE Na in prerenal failure is significantly lower than ATN. A FE UN has no benefit in distinguishing betweenprerenal failure and ATN. Furosemide has no effect on both FENa and FE UN. Acute renal failure Prerenal failure Acute tubular necrosis Fractional excretion of sodium Fractional excretionof urea Furosemide