The value is lower in early disease, but with kidney damage from the obstruction, the value becomes higher.Įxceptions in children and neonates In renal tract obstruction, values may be either higher or lower than 1%. low output heart failure).Īcute tubular necrosis or other kidney damage (postrenal disease)Įither excess sodium is lost due to tubular damage, or the damaged glomeruli result in hypovolemia resulting in the normal response of sodium wasting. The physiologic response to a decrease in kidney perfusion is an increase in sodium reabsorption to control hyponatremia, often caused by volume depletion or decrease in effective circulating volume (e.g. The FE Na may be affected or invalidated by diuretic use, since many diuretics act by altering the kidney's handling of sodium. Higher values can suggest sodium wasting due to acute tubular necrosis or other causes of intrinsic kidney failure. Low fractional excretion indicates sodium retention by the kidney, suggesting pathophysiology extrinsic to the urinary system such as volume depletion or decrease in effective circulating volume (e.g. the 'fraction' excreted).įE Na can be useful in the evaluation of acute kidney failure in the context of low urine output. The flow rates cancel out in the above equation, simplifying to the standard equation: į E N a = 100 × s o d i u m u r i n a r y × c r e a t i n i n e p l a s m a s o d i u m p l a s m a × c r e a t i n i n e u r i n a r y įor ease of recall, one can just remember the fractional excretion of sodium is the clearance of sodium divided by the glomerular filtration rate (i.e. This formula is represented mathematically as: This is calculated by multiplying the plasma sodium concentration by the glomerular filtration rate calculated using creatinine filtration. The denominator is the total amount of sodium filtered by the kidneys. įirst, the actual amount of sodium excreted is calculated by multiplying the urine sodium concentration by the urinary flow rate. In clinical use, the fractional excretion of sodium 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.įE Na is calculated in two parts-figuring out how much sodium is excreted in the urine, and then finding its ratio to the total amount of sodium that passed through (aka 'filtered by') the kidney. Therefore, the urinary and plasma concentrations of sodium must be compared to get an accurate picture of kidney clearance. It is measured in terms of plasma and urine sodium, rather than by the interpretation of urinary sodium concentration alone, as urinary sodium concentrations can vary with water reabsorption. The fractional excretion of sodium (FE Na) is the percentage of the sodium filtered by the kidney which is excreted in the urine. Pathophysiology sample values BMP/ ELECTROLYTES:

Urine sodium normal range pediatric