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Sodium, 24-Hour Urine

CPT: 84300
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Special Instructions

The test request form must state date and time collection started, date and time collection finished, and 24-hour urine volume.

Expected Turnaround Time

Within 1 day

Related Information

Related Documents

Specimen Requirements


Urine (24-hour)


10 mL aliquot

Minimum Volume

1 mL aliquot (Note: This volume does not allow for repeat testing.)


Plastic urine container without preservative


Instruct the patient to void at 8 AM and discard the specimen. Then collect all urine including the final specimen voided at the end of the 24-hour collection period (ie, 8 AM the next morning). Screw the lid on securely. Container must be labeled with patient's full name, date and time collection started, and date and time collection finished.

Storage Instructions

Room temperature

Stability Requirements



Room temperature

14 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Improper labeling

Test Details


Work up volume depletion, acute renal failure, acute oliguria, and differential diagnosis of hyponatremia.1 Division of hyponatremia into hypervolemia or not, edema or not, and urinary Na+ less than or greater than 10 mmol/L provides a classification of hyponatremia.2 History of diuretics, other drug intake, setting of osmotic diuresis or not, serum or plasma electrolytes and other factors are needed.


Ion-selective electrode (ISE); flame photometer

Reference Interval


Male (mmol/24 hr)

Female (mmol/24 hr)

0 to 5 y

Not established

Not established

6 to 12 y

Not established


13 to 17 y



18 to 80 y



>80 y



Additional Information

In cases of hyponatremia, urine sodium <10 mmol/L may indicate extrarenal depletion: dehydration (gastrointestinal or sweat loss), congestive heart failure, liver disease or nephrotic syndromes.

Urine sodium >10 mmol/L may indicate diuretics, emesis, intrinsic renal diseases, Addison disease, hypothyroidism, or syndrome of inappropriate antidiuretic hormone (SIADH).2 In hypothyroidism and in SIADH, Na+ and Cl- may be >40 mmol/L.3 (Depending on intake, such results also can be found in normal individuals.) In SIADH, urinary sodium is usually >20 mmol/L. Inappropriate secretion of antidiuretic hormone (SIADH) was found in 7% of 250 patients with small cell lung cancer.4 Such patients have hyponatremia, often severe, with hypo-osmolar serum, high urinary sodium excretion with urine osmolality greater than that of serum. Acute and subacute diseases of the CNS, TB and other chronic pulmonary diseases may also cause SIADH. SIADH may also be caused by acute intermittent porphyria, LE, occasional malignant neoplasms other than small cell carcinoma of lung, and a number of drugs.5

The classification as presented here is overly abbreviated for clinical application. Pitfalls exist (eg, increase of Na+ necessary to balance excretion of penicillin).3

Urine Na+ >40 mmol/L in oliguria suggests acute tubular necrosis.3,6 (However, spot urine sodiums without other data have been criticized for their applicability to this diagnosis.)

Low Na+ excretion may be found with early obstructive uropathy and with the oliguria of acute glomerulonephritis3 and in some patients with x-ray contrast acute renal failure.

Silver et al recommend measurement of urinary Na+ excretion in patients with nephrolithiasis and hypercalciuria.7

It is important to know the urinary sodium level in patients with unexplained hyperchloremic metabolic acidosis when the diagnosis of distal renal tubular acidosis is being considered.8


1. Harrington JT, Cohen JJ. Measurement of urinary electrolytes—indications and limitations. N Engl J Med. 1975 Dec 11; 293(24):1241-1243. 1186803
2. Epstein M, Oster JR. Disorders of hyponatremia and hypernatremia. In: Halsted JA, Halsted CH, eds.The Laboratory in Clinical Medicine: Interpretation and Application. 2nd ed. Philadelphia, Pa: WB Saunders Co;1981:289-295.
3. Sherman RA, Eisinger RP. The use (and misuse) of urinary sodium and chloride measurements. JAMA. 1982 Jun 11; 247(22):3121-3124. 7077808
4. Hainsworth JD, Workman R, Greco FA. Management of the syndrome of inappropriate antidiuretic hormone secretion in small cell lung cancer. Cancer. 1983 Jan 1; 51(1):161-165. 6295592
5. Streeten DH, Moses AM, Miller M. Disorders of the neurohypophysis. In: Braunwald E, Isselbacher KJ, Petersdorf RG, et al, eds. Harrison's Principles of Internal Medicine. New York, NY: McGraw-Hill Information Services Co;1987:1722-1732.
6. Schrier RW. Acute renal failure. JAMA. 1982 May 14; 247(18):2518-2522, 2524. 7069917
7. Silver J, Rubinger D, Friedlaender MM, Popovtzer MM. Sodium-dependent idiopathic hypercalciuria in renal-stone formers. Lancet. 1983 Aug 27; 2(8348):484-486. 6136646
8. Batlle DC, von Riotte A, Schlueter W. Urinary sodium in the evaluation of hyperchloremic metabolic acidosis. N Engl J Med. 1987 Jan 15; 316(3):140-144. 3796685


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
003178 Sodium, 24 hr Urine 2956-1 013326 Sodium, Urine mmol/L 21525-1
003178 Sodium, 24 hr Urine 2956-1 013268 Sodium, Urine mmol/24 hr 2956-1

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