What is the appropriate workup for hyponatremia (low sodium levels)?

From the Guidelines

The appropriate workup for hyponatremia involves determining the underlying cause, which can be categorized into hypovolemic, euvolemic, or hypervolemic hyponatremia, and managing it accordingly.

Evaluation of Hyponatremia

• The evaluation of hyponatremia in patients with cirrhosis and ascites should consider the severity and chronicity of hyponatremia, as well as the presence of symptoms 1.
• Hypovolemic hyponatremia can occur due to poor oral intake or excessive diuretic or laxative use, and treatment involves fluid resuscitation with 5% IV albumin or crystalloid solution 1.
• Euvolemic hyponatremia is uncommon in cirrhosis, but can be caused by syndrome of inappropriate antidiuretic hormone secretion, certain medications (e.g., sertraline, carbamazepine), or severe hypothyroidism or adrenal insufficiency 1.
• Hypervolemic hyponatremia is the most common type in cirrhosis, and treatment includes fluid restriction, reduction or discontinuation of diuretics and laxatives, administration of hyperoncotic albumin, and/or vasopressin receptor antagonists (“vaptans”) 1.

Management of Hyponatremia

• Mild hyponatremia (Na 126-135 mEq/L) in cirrhosis without symptoms does not require specific management apart from monitoring and water restriction 1.
• Moderate hyponatremia (120-125 mEq/L) should be managed with water restriction to 1,000 mL/day and cessation of diuretics, while severe hyponatremia (<120 mEq/L) requires a more severe restriction of water intake with albumin infusion 1.
• The goal rate of increase of serum sodium in chronic hyponatremia is 4-6 mEq/L per 24-hour period, not to exceed 8 mEq/L per 24-hour period to ameliorate the risk of osmotic demyelination syndrome (ODS) 1.

From the Research

Diagnosis of Hyponatremia

The diagnosis of hyponatremia involves a systematic approach to laboratory diagnosis, including measurement of the effective serum tonicity (serum osmolality less serum urea level) 2. The following steps can be taken:

• Measure serum osmolality and urine osmolality to determine whether water excretion is normal or impaired
• Assess extracellular volume status on physical examination to provide useful clues as to the pathogenesis of hyponatremia
• Determine urine sodium level to indicate whether hypovolemia or the syndrome of inappropriate antidiuretic hormone secretion is present

Classification of Hyponatremia

Hyponatremia can be classified based on volume status, including:

• Hypovolemic hyponatremia: treated with normal saline infusions 3
• Euvolemic hyponatremia: treated with restricting free water consumption or using salt tablets or intravenous vaptans 3
• Hypervolemic hyponatremia: treated primarily by managing the underlying cause (e.g., heart failure, cirrhosis) and free water restriction 3

Treatment of Hyponatremia

The treatment of hyponatremia depends on the severity of symptoms and the underlying cause. The following treatments can be used:

• Hypertonic saline to treat severe symptomatic hyponatremia 4, 3, 5
• Fluid restriction in the setting of euvolemia 6
• Isotonic saline in hypovolemia 6
• Diuresis in hypervolemia 6
• Vaptans may have a role in the treatment of euvolemic and hypervolemic hyponatremia 4, 6

Monitoring and Correction of Sodium Levels

It is essential to monitor sodium levels closely to avoid overly rapid correction, which can cause osmotic demyelination syndrome 3, 5. The correction limit for sodium levels is 10 mEq/L within the first 24 hours 4. Calculators can be used to guide fluid replacement and avoid overly rapid correction of sodium concentration 3.