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Sodium Urine

Dietary intake greatly influences the urinary excretion of sodium. The rate of sodium excretion during the night is only one‑fifth of the peak rate during the day, indicating a large diurnal variation. Measurement of urinary sodium is helpful in the differential diagnosis of hyponatremia and hypernatremia.

Urine Sodium Concentration in Patients with Hyponatremia

Fluid Volume

Urinary Sodium

Causes

Hypovolemia

>20

Renal losses due to diuretics, aldosterone deficiency, salt losing nephropathy, osmotic diuresis, ketonuria, RTA

<20

Extra renal losses due to vomiting, diarrhea, third spacing of fluids from burns, pancreatitis, trauma

Euvolemia

>20

Cortisol deficiency, hypothyroidism, stress, drugs, SIADH

Hypervolemia

>20

Acute or chronic renal failure

<20

Nephrotic syndrome, cirrhosis, cardiac failure

 

Urine Sodium Concentration in Patients with Hypernatremia

Fluid Volume

Urinary Sodium

Causes

Hypovolemia

<20

Excess sweating, burns, diarrhea, fistulas

>20

Renal disease, urinary tract obstruction, osmotic or loop diuretics

Euvolemia

Variable

Diabetes insipidus, hypodipsia, Insensible losses, respiratory, dermal

Hypervolemia

>20

Primary hyperaldosteronism, Cushing’s syndrome, hypertonic dialysis, hypertonic sodium bicarbonate, sodium chloride tablets

Reference range is 43 - 217 mEq/24 hours.

Specimen requirement is a 24 hour urine collection in a container without preservative. Specimen should be refrigerated during an after the collection.

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