Type of test Blood
Normal findings
Adult/elderly: 136-145 mEq/L or 136-145 mmol/L (SI units)
Child: 136-145 mEq/L
Infant: 134-150 mEq/L
Newborn: 134-144 mEq/L
Possible critical values < 120 or > 160 mEq/L
Test explanation and related physiology
Sodium is the major cation in the extracellular space, in which serum levels of approximately 140 mEq/L exist. Therefore sodium salts are the major determinants of extracellular osmolality. The sodium content of the blood is a result of a balance between dietary sodium intake and renal excretion.
Many factors regulate homeostatic sodium balance. Aldosterone causes conservation of sodium by decreasing renal losses. Natriuretic hormone, or third factor, increases renal losses of sodium. Antidiuretic hormone (ADH), which controls the resorption of water at the distal tubules of the kidney, also affects serum sodium levels.
Physiologically, water and sodium are very closely interrelated. As free body water is increased, serum sodium is diluted, and the concentration may decrease. The kidney compensates by conserving sodium and excreting water. If free body water were to decrease, the serum sodium concentration would rise; the kidney would then respond by conserving free water.
Interfering factors
• Recent trauma, surgery, or shock may cause increased levels.
* Drugs that may cause increased levels include anabolic steroids, antibiotics, carbenicillin, clonidine, corticosteroids, cough medicines, estrogens, laxatives, methyldopa, and oral contraceptives.
* Drugs that may cause decreased levels include angiotensin converting enzyme inhibitors, captopril, carbamazepine, diuretics, haloperidol, heparin, nonsteroidal antiinflammatory drugs, intravenous (IV) fluids, sulfonylureas, triamterene, tri cyclic antidepressants, and vasopressin.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: red or green
Abnormal findings
Increased levels (hypernatremia)
Increased sodium intake
- Excessive dietary intake
- Excessive sodium in IV fluids
Decreased sodium loss
- Cushing syndrome
- Hyperaldosteronism
Excessive free body water loss
- Excessive sweating
- Extensive thermal burns
- Diabetes insipidus
- Osmotic diuresis
- GI loss
Decreased levels (hyponatremia)
Decreased sodium intake
- Deficient dietary intake
- Deficient sodium in IV fluids
Increased sodium loss
- Addison disease
- Diarrhea
- Vomiting or nasogastric aspiration
- Diuretic administration
- Chronic renal insufficiency
- Increased free body water
- Excessive oral water intake
- Excessive IV water intake
- Congestive heart failure
- Syndrome of inappropriate ADH (SIADH) secretion
- Osmotic dilution
-Third-space losses of sodium
- Ascites
- Peripheral edema
- Pleural effusion
- Intraluminal bowel loss (ileus or mechanical obstruction)
