Sodium

Keywords: Natrium, Na

Specimen:

5 mL blood in lithium heparin or plain tube.

Method:

ISE, flame emission spectrophotometry.

Reference Interval:

See Table 6.

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.