Sodium (NA)

CPT Code: 



Serum or heparinized plasma 


1 mL 

Minimum Volume: 

0.5 mL 


Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube


Ion-selective electrode (ISE); flame photometer


Serum is obtained by collecting blood in an untreated blood collection tube.  The sample should stand for 30 minutes to allow the clot to form prior to centrifugation.

Specimen tubes should be centrifuged unopened and the serum or plasma should be separated within one hour after venipuncture.

Sera or plasma separated from cells that are stored for several hours prior to analysis should be inspected for delayed fibrin clot formation.  If delayed clot formation is detected or suspected, the sample should be centrifuged before analysis.

Whole blood specimens cannot be analyzed.

Reference Range:

136-145 mmol/L 


Temperatures  Period 
Room Temperature  1 week 
Refrigerated (2-8 ⁰C)  1 week 



Sodium, a major electrolyte, is present in body fluids, and plays a key role in salt and water balance. 

Clinical Significance:

Hypernatremia occurs in dehydration. For instance, nasogastric protein feeding with insufficient fluids may cause hypernatremia. Hypernatremia without obvious cause may relate to Cushing syndrome, central or nephrogenic diabetes insipidus with insufficient fluids, primary aldosteronism, and other diseases. Severe hypernatremia may be associated with volume contraction, lactic acidosis, azotemia, weight loss, and increased hematocrit as evidence of dehydration. The corrected serum sodium is often high in nonketotic hyperosmolar coma. Hyponatremia occurs with nephrotic syndrome, cachexia, hypoproteinemia, intravenous glucose infusion, in congestive heart failure, and other clinical entities. Serum sodium is a predictor of cardiovascular mortality in patients in severe congestive heart failure.

Hyponatremia without congestive failure or dehydration may occur with hypothyroidism, the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), renal failure, or renal sodium loss.

The differential diagnosis of hyponatremia includes Addison disease, hypopituitarism, liver disease including cirrhosis, hypertriglyceridemia, and psychogenic polydipsia. Diuretics and other drugs may cause hyponatremia. Sodium decreasing to levels <115 mmol/L can lead to significant neurological dysfunction with cerebral edema and increased intracranial pressure.

Causes for Rejection: 

Hemolysis; improper labeling 

Interfering Substances:

Samples exposed to Benzalkonium salts present in certain blood catheter devices will cause falsely elevated sodium measurements.

Citrate at a test concentration of 52.9 mmol/L decreases sodium by 38 mmol/L.

Thiopental increases sodium results by as much as 8 mmol/L at 14 mg/dL of thiopental and up to 4 mmol/L at 2.8 mg/dL of thiopental.