P1: SBT
0521779407-02 CUNY1086/Karliner 0 521 77940 7 June 7, 2007 19:18
Acute Renal Failure 51➣Acute glomerulonephritis
Protein, blood on dipstick; RBCs (often dysmorphic), RBC
casts, WBCs on sediment
➣Intrarenal obstruction
Large number of crystals (oxalate, uric acid, etc)
■2. Urine chemistries (urinary indices)
➣Most helpful if oliguric
➣Only use in conjunction with history, physical and urine sedi-
ment – not in isolation
➣FENa=(UNa/PNa divided by UCr/PCr)×^100
U is urine concentration
P plasma sodium (Na) or creatinine (Cr)
➣Prerenal: UNa, <20, FENa <1
➣ATN: UNa >20, FENa >2
FeUN=(UBUN/PBUN divided by UCr/PCr)×100. FEUN <35% may be
more sensitive and specific index than FENa in differentiating between
prerenal ARF and ATN, especially if diuretics have been used.
Urine Neutrophil gelatinase-associated lipocalin (NGAL) levels are
increased in children with ischemic ATN after cardiac surgery; further
studies necessary to clarify role in diagnosis.Imaging
■1. Ultrasound
➣Useful to evaluate the urinary collecting system, rule out urinary
obstruction
■2. Doppler scans, nuclear scans
➣Only useful to rule out vascular occlusion – otherwise, not useful
■3. MRI
➣Gold standard for diagnosis of renal vein thrombosis; may also
be useful to diagnose renal artery stenosis or occlusionRenal Biopsy
■Should be considered in any patient with ARF in whom etiology
is unknown, and whom treatment may be instituted (i.e., possible
rapidly progressive glomerulonephritis)
differential diagnosis
■ARF or CRF?
➣Sometimes difficult to distinguish
➣Prior BUN, creatinine, urinalyses invaluable
➣Prolonged history of fatigue, anorexia, pruritus suggests chronic
renal failure.