Sodium - urine
Last updated: Saturday, 27, March, 2004
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| Item | Process |
|---|---|
| Specimen | Random or 24 hour urine collection. |
| Method | ISE or flame emission spectrophotometry. |
| Reference Interval | In hyponatraemia or hypovolaemic shock without acute tubular necrosis, urine sodium should be <20 mmol/L and fractional excretion of sodium should be <1.5%. If extracellular fluid volume and plasma sodium are normal, urine sodium should equal intake minus non-renal losses, typically 75-300 mmol/24 hours. |
| Application | Investigation of hyponatraemia. Assessment of renal function in hypovolaemic shock. Investigation of compliance with a low sodium diet. Investigation of predisposing factors for hypercalciuria in patients with renal calculi. |
| Interpretation | Urinary sodium excretion exceeds 20 mmol/L in hyponatraemia due to SIADH, diuretic therapy, or Addison’s disease. In a patient with shock and oliguria a urinary sodium >20 mmol/L or a fractional excretion of sodium >1.5% suggests acute tubular necrosis. High urine sodium increases urine calcium and predisposes to calculi containing calcium. |
| Reference | Halperin ML and Bohn D. Crit Care Clin. 2002; 18(2): 249-272. |