Sodium urine

Keywords: Urine sodium, Urine Na

Specimen:

Random or 24 h urine collection.

Method:

ISE, 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 h.

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.