Specimen Collection
2 mL Urine (Random)
24hr Urine
Reference Intervals

Reference interval:

The output of sodium in the urine depends on the sodium intake, if the patient is in a steady state.

Less than 100 mmol/d : low sodium intake

100 - 200 mmol/d: average sodium intake

>200 mmol/d : high sodium intake

There is a large diurnal variation in sodium excretion, being much lower at night.

Uncertainty of Measurement: 5%

Turnaround Time: Within 3 hours
Assay Method

Principle : Ion selective electrode

Reagents: Roche Sodium electrode

Analyser: Cobas Indirect ISE

Diagnostic Use and Interpretation

The urinary sodium concentration may be helpful in determining the cause of hyponatraemia or oliguria.

In a hyponatraemic patient, a low urine sodium (< 20 mmol/L) indicates a strong aldosterone drive, suggesting that hypovolaemia or sodium depletion is present.

In an oliguric patient, a low urine sodium (< 20 mmol/L) indicates prerenal uraemia, rather than intrinsic acute renal failure.

In a hyponatremic patient, urine sodium concentrations > 40 mmol/L are typically seen in SIADH, Addison's disease, renal tubular damage or diuretic-induced hyponatraemias. However low urinary sodium does not exclude these conditions if sodium depletion is present.

Contact Information

The chemical pathology team can be reached via email: chemicalpathologist@adhb.govt.nz or via Lablink (09) 307 4949 ext 22000 or 09-3078995

Emails will receive priority attention from the on-call chemical pathologist. Include the patients NHI.

After-hours: contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours .

• Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
• Dr Cam Kyle : CampbellK@adhb.govt.nz ext 22052
• Dr Weldon Chiu : WeldonC@adhb.govt.nz ext. 23427
• Dr Campbell Heron : CHeron@adhb.govt.nz ext. 23427
• Dr Sakunthala Jayasinghe Saku.Jayasinghe@adhb.govt.nz
• Dr Owen Yi WenyiYi@adhb.govt.nz

Last updated at 11:42:03 16/01/2026