Sodium, Urine

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Subject: Sodium, Urine

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Definition

  • Urinary sodium determinations are usually performed to detect or confirm the presence of conditions that affect body fluids (e.g., dehydration, vomiting, and diarrhea) or disorders of the kidneys or adrenal glands.

  • Normal range:

    • Twenty-four–hour urine:

      • Male:

        • Less than 10 years: 41–115 mmol/day

        • 10–14 years: 63–177 mmol/day

        • Greater than 14 years: 40–120 mmol/day

      • Female:

        • Less than 10 years: 20–69 mmol/day

        • 10–14 years: 48–168 mmol/day

        • Greater than 14 years: 27–287 mmol/day

    • Random urine

      • Male: 23–229 mmol/g creatinine

      • Female: 26–297 mmol/g creatinine

Use

  • Volume depletion: to determine the route of sodium loss. Low urinary sodium indicates extrarenal loss, and high value indicates renal salt wasting or adrenal insufficiency.

  • Differential diagnosis of acute renal failure: high values are consistent with acute tubular necrosis.

  • In hyponatremia, low urinary sodium indicates avid renal sodium retention, which may be attributable to either severe volume depletion or sodium-retaining states seen in cirrhosis, the nephrotic syndrome, and CHF. When hyponatremia is associated with urinary sodium excretion that equals or exceeds the dietary sodium intake, it is likely that SIADH is present.

Interpretation

Increased In

  • Dehydration

  • Salicylate intoxication

  • Adrenocortical insufficiency

  • Diabetic acidosis

  • Mercurial and thiazide diuretic administration

  • Ammonium chloride administration

  • Renal tubular acidosis (<15 mmol/L are seen in prerenal acidosis)

  • Chronic renal failure

  • SIADH of different etiology

  • Any form of alkalosis and alkaline urine

Decreased In

  • Acute renal failure

  • Pulmonary emphysema

  • CHF

  • Excessive sweating

  • Diarrhea

  • Pyloric obstruction

  • Malabsorption

  • Primary aldosteronism

  • Premenstrual sodium and water retention

  • Acute oliguria and prerenal azotemia

Limitations

  • Large diurnal variations exist in urine sodium levels. The rate of excretion during night is one fifth of the peak rate during the day.

  • Levels are highly dependent on dietary intake and state of hydration.

 
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