Urine Sodium

Random or Timed Urine Specimen

Collect random or timed specimen per orders.  For timed specimen, record start and stop time of collection or number of hours.  To transfer specimen from large container to smaller container for transport, measure volume first and record on smaller container, along with time.  Timed specimens are typically collected for 24 hours, but can be collected in other increments, for example, 4 hours or 12 hours.

This test is for Sodium measurement on Urine.  For Sodium measurement on Plasma or Serum, order NA.  For Sodium measurement on Body Fluids, order MISNA.

24-hour urine container or sterile urine cup

Monday - Sunday, 8:00 am - 3:00 pm upon receipt

Urine Volume:  800 - 1800 mL/24 hours
Urine Sodium/Total Volume Ratio:  40 - 220 mmol/24 hours

The Urine Sodium test is useful for assessing acid-base balance, water balance, water intoxication, and dehydration.

Sodium (Na+) is the primary extracellular cation.  Sodium is responsible for almost one half the osmolality of the plasma and, therefore, plays a central role in maintaining the normal distribution of water and the osmotic pressure in the extracellular fluid compartment.  The amount of Na+ in the body is a reflection of the balance between Na+ intake and output.  The normal daily diet contains 8 to 15 grams of sodium chloride (NaCl) which is nearly completely absorbed from the gastrointestinal tract.  The body requires only 1 to 2 mmol/d, and the excess is excreted by the kidneys, which are the ultimate regulators of the amount of Na+ (and thus water) in the body.  Sodium is freely filtered by the glomeruli.  Approximately 70% to 80% of the filtered Na+ is actively reabsorbed in the proximal tubules with chloride and water passively following in an iso-osmotic and electrically neutral manner.  Another 20% to 25% is reabsorbed in the loop of Henle along with chloride and more water.  In the distal tubules, interaction of the adrenocortical hormone aldosterone with the coupled sodium-potassium and sodium-hydrogen exchange systems directly results in the reabsorption of Na+ and indirectly of chloride from the remaining 5% to 10% of the filtered load.  It is the regulation of this latter fraction of filtered Na+ that determines the amount of Na+ excreted in the urine.

Urinary sodium (Na+) excretion varies with dietary intake, and there is a large diurnal variation with the rate of Na+ excretion during the night being only 20% of the peak rate during the day.

Sodium may be lost in the kidneys as a result of diuretic therapy, salt-losing nephropathies, or adrenal insufficiency, with the urinary Na+ concentration usually more than 20 mmol/L.  In these hypovolemic states, urine Na+ values < 10 mmol/L indicate extrarenal Na+ loss.  In hypervolemic states, a low urine Na+ (< 10 mmol/L) may indicate nephrotic syndrome in addition to non-renal causes.

This test is for Sodium measurement on Urine.   For Sodium measurement on Plasma or Serum, order NA.  For Sodium measurement on Body Fluids, order MISNA.