<unk>  can be useful in the evaluation of acute kidney failure in the context of low urine output. Low<unk>  excretion indicates<unk>  retention by the kidney, suggesting pathophysiology extrinsic to the urinary system such as volume depletion or decrease in effective circulating volume (e.g. low output heart failure). Higher values can suggest<unk>  wasting due to acute tubular necrosis or other causes of intrinsic kidney failure. The<unk>  may be affected or invalidated by diuretic use, since many diuretics act by altering the kidney's handling of<unk> . Value Category Description below 1% prerenal disease the physiologic response to a decrease in kidney perfusion is an increase in<unk>  reabsorption to control hyponatremia, often caused by volume depletion or decrease in effective circulating volume (e.g. low output heart failure). above 2% or 3% acute tubular necrosis or other kidney damage (postrenal disease) either excess<unk>  is lost due to tubular damage, or the damaged glomeruli result in hypovolemia resulting in the normal response of<unk>  wasting. intermediate either disorder In renal tract obstruction, values may be either higher or lower than 1%. The value is lower in early disease, but with kidney damage from the obstruction, the value becomes higher.
Fractional excretion of sodium
Plasma renin activity
Urine osmolality
Aldosterone-to-renin ratio
Net acid excretion
Urine flow rate
Urine urea nitrogen
Glomerular filtration rate