The<unk>  <unk>  is the percentage of the<unk>  filtered by the kidney which is excreted in the urine. It is measured in terms of plasma and urine<unk> , rather than by the interpretation of urinary<unk>  concentration alone, as urinary<unk>  concentrations can vary with water reabsorption. Therefore, the urinary and plasma concentrations of<unk>  must be compared to get an accurate picture of kidney clearance. In clinical use, the<unk>  can be calculated as part of the evaluation of acute kidney failure in order to determine if hypovolemia or decreased effective circulating plasma volume is a contributor to the kidney failure.
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