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

From the Guidelines

The workup for hyponatremia should begin with a thorough history, physical examination, and basic laboratory tests to determine the cause and guide treatment, with a focus on assessing volume status and correcting sodium levels at a rate not exceeding 8 mEq/L in 24 hours to prevent osmotic demyelination syndrome 1. The initial laboratory evaluation should include serum sodium, potassium, chloride, bicarbonate, blood urea nitrogen, creatinine, glucose, and osmolality, along with urine sodium and osmolality. Key considerations in the management of hyponatremia include:

• Assessment of volume status, categorizing the patient as hypovolemic, euvolemic, or hypervolemic
• For hypovolemic hyponatremia, fluid resuscitation with isotonic saline (0.9% NaCl) is appropriate
• Euvolemic hyponatremia often indicates SIADH and may require fluid restriction to 800-1000 mL/day, with consideration of salt tablets, urea (15-30 g/day), or vasopressin receptor antagonists like tolvaptan (starting at 15 mg daily) in resistant cases
• Hypervolemic hyponatremia typically requires treatment of the underlying condition (heart failure, cirrhosis, nephrotic syndrome) along with fluid restriction and diuretics like furosemide (20-40 mg daily)
• In patients with cirrhosis, mild hyponatremia (Na 126-135 mEq/L) does not require specific management apart from monitoring and water restriction, while moderate hyponatremia (120-125 mEq/L) requires water restriction to 1,000 mL/day and cessation of diuretics 1. Additional testing may include thyroid function tests, cortisol levels, and medication review to identify contributing factors such as thiazide diuretics, SSRIs, carbamazepine, or NSAIDs. The goal rate of increase of serum sodium in patients with cirrhosis 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 1.

From the Research

Hyponatremia Workup

• Hyponatremia is defined as a serum sodium level of less than 135 mEq/L and is the most common electrolyte disorder, affecting approximately 5% of adults and 35% of hospitalized patients 2.
• The approach to managing hyponatremia should consist of treating the underlying cause, and patients should be categorized according to their fluid volume status (hypovolemic hyponatremia, euvolemic hyponatremia, or hypervolemic hyponatremia) 2.

Diagnosis and Treatment

• The diagnosis of hyponatremia involves confirming the presence of hypoosmolality and determining the origin and acuity of the condition 3.
• Treatment options for hyponatremia include hypertonic saline, isotonic saline, water restriction, long loops diuretics, urea, and vaptans 3.
• Urea and vaptans can be effective treatments for the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure, but have adverse effects 2, 4.
• Hypertonic saline is reserved for patients with severely symptomatic hyponatremia, and its use should be guided by clinical practice guidelines to avoid harm 5, 6.

Clinical Practice Guidelines

• The European Society of Intensive Care Medicine (ESICM), the European Society of Endocrinology (ESE), and the European Renal Association-European Dialysis and Transplant Association (ERA-EDTA) have developed clinical practice guidelines on the diagnostic approach and treatment of hyponatremia 6.
• These guidelines focus on patient-positive outcomes and provide a useful tool for clinicians involved in everyday practice 6.
• The guidelines recommend treating severely symptomatic hyponatremia with bolus hypertonic saline to reverse hyponatremic encephalopathy, but also emphasize the importance of limiting the daily increase of serum sodium to less than 8-10 mmol/liter to avoid osmotic demyelination 2, 4.