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, with the most recent guidelines suggesting a careful approach to sodium correction, not exceeding 8 mmol/L per day, as recommended by the 2021 guidelines on the management of ascites in cirrhosis 1. The initial steps in the workup should include assessment of volume status, categorizing the patient as hypovolemic, euvolemic, or hypervolemic. For hypovolemic hyponatremia, evaluation for gastrointestinal losses, diuretic use, or third-spacing is crucial. In euvolemic hyponatremia, consider SIADH (Syndrome of Inappropriate Antidiuretic Hormone), hypothyroidism, adrenal insufficiency, or medication effects. For hypervolemic states, assess for heart failure, cirrhosis, or nephrotic syndrome. Some key points to consider in the management of hyponatremia include:

• Initial labs should include serum sodium, potassium, chloride, bicarbonate, blood urea nitrogen, creatinine, glucose, and osmolality, along with urine sodium and osmolality, as suggested by the 2018 kasl clinical practice guidelines for liver cirrhosis: ascites and related complications 1.
• Medication review is essential as many drugs can cause hyponatremia, including SSRIs, diuretics, antiepileptics, and certain antipsychotics.
• The rate of sodium correction should be carefully planned based on symptom severity, with severe symptomatic hyponatremia requiring more urgent correction, as recommended by the 2018 easl clinical practice guidelines for the management of patients with decompensated cirrhosis 1.
• Treatment should always target the underlying cause while managing the sodium level appropriately, with the use of hypertonic sodium chloride administration reserved for those who are severely symptomatic with acute hyponatremia, as suggested by the 2021 guidelines on the management of ascites in cirrhosis 1. The most recent and highest quality study, the 2021 guidelines on the management of ascites in cirrhosis 1, provides the most up-to-date recommendations for the management of hyponatremia, emphasizing the importance of careful sodium correction and treatment of the underlying cause.

From the Research

Hyponatremia Workup

• Hyponatremia is defined by a serum sodium level of less than 135 mEq/L and most commonly results from water retention 2.
• The approach to managing hyponatremia should consist of treating the underlying cause, and clinicians should categorize patients according to their fluid volume status (hypovolemic hyponatremia, euvolemic hyponatremia, or hypervolemic hyponatremia) 2, 3.
• Evaluation of hyponatremia begins with a detailed history and physical examination, and appropriate urine and serum studies can contribute to the evaluation and classification of the disorder 3, 4.
• Measurement of the effective serum tonicity (serum osmolality less serum urea level) is the first step in the laboratory evaluation, and urine osmolality is used to determine whether water excretion is normal or impaired 5, 4.
• A urine sodium level less than 20 mmol/L is indicative of hypovolemia, whereas a level greater than 40 mmol/L is suggestive of the syndrome of inappropriate antidiuretic hormone secretion 4.

Diagnosis and Classification

• Hyponatremia can be classified into three main categories: hypovolemic, euvolemic, and hypervolemic hyponatremia 2, 3.
• The clinical manifestations of hyponatremia include headache, dizziness, nausea/vomiting, seizures, obtundation, and death 3.
• Determination of the etiology of chronic hyponatremia requires analysis of serum osmolality, volume status, and urine osmolality and sodium level 6.

Treatment

• Treatment decisions are based on the underlying cause and severity of symptoms, and most patients should be managed by treating their underlying disease 2, 3.
• Urea and vaptans can be effective in managing the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure 2.
• Hypertonic saline is reserved for patients with severely symptomatic hyponatremia, and the goal is to increase the serum sodium level by 4-6 mEq/L within 1-2 hours but by no more than 10 mEq/L within the first 24 hours 2, 6.
• Overly aggressive correction of serum sodium levels can result in neurological injury caused by osmotic demyelination 2, 6.