Sodium - plasma or serum

Last updated: Friday, 04, June, 2010

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Item Process
Specimen

5 mL blood in lithium heparin or plain tube.

MethodFlame emission spectrophotometry or ISE.
Reference Interval

135-145 mmol/L.

Application

Assessment and monitoring of fluid and electrolyte status, particularly in patients with renal or cardiac disease, possible sodium losing states, and in those receiving intravenous fluids.

Interpretation

Sodium concentration is dependent on the state of hydration, body sodium content and water shifts between plasma and other body fluid compartments.

Intravenous therapy with isotonic saline may cause hypernatraemia and volume replacement with dextrose may cause hyponatraemia.
Hyponatraemia occurs in a small percentage of patients on diuretic therapy, particularly the elderly. Severe hyper­lipidaemia or hyperproteinaemia may cause 'pseudohyponatraemia'.
See Table 1.

Sodium is retained with mineralocorticoid excess and lost with mineralocorticoid deficiency, gastrointestinal and renal loss, or excessive sweating.

Hypo­natraemia as a result of fluid retention (dilutional hyponatraemia) is seen in renal and cardiac disease and with SIADH. Urine sodium estimation may assist in interpretation; see Sodium - urine.

Reference

Halperin ML and Bohn D. Crit Care Clin 2002; 18(2): 249-272.