From the Guidelines
Diagnosing the cause of hyponatremia requires a systematic approach starting with a thorough clinical assessment and targeted laboratory testing, as outlined in the 2013 ACCF/AHA guideline for the management of heart failure 1. To diagnose the cause of hyponatremia, begin by obtaining a comprehensive history, including medication use (especially diuretics, antidepressants, and antipsychotics), fluid intake, and symptoms.
- Physical examination should assess volume status by checking for edema, skin turgor, mucous membrane moisture, blood pressure, and heart rate.
- Essential laboratory tests include serum sodium, potassium, glucose, creatinine, blood urea nitrogen, serum and urine osmolality, and urine sodium.
- Categorize the hyponatremia by volume status:
- Hypovolemic (urine sodium <20 mEq/L in renal losses, >20 mEq/L in extrarenal losses)
- Euvolemic (SIADH with urine sodium >20 mEq/L and inappropriately concentrated urine)
- Hypervolemic (heart failure, cirrhosis with urine sodium <20 mEq/L) Additional tests may include thyroid and adrenal function tests, as hypothyroidism and adrenal insufficiency can cause hyponatremia, with serum cortisol, TSH, and free T4 measured when clinically indicated 1. In cases of euvolemic hyponatremia, consider chest imaging to rule out occult malignancy that might cause SIADH. This systematic approach helps identify the underlying cause, which is crucial for appropriate treatment selection, as vasopressin antagonists may be considered in the short term to improve serum sodium concentration in hypervolemic, hyponatremic states 1.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Diagnosis of Hyponatremia
To diagnose the cause of hyponatremia, the following steps can be taken:
- Evaluate the patient's fluid volume status, which can be categorized into hypovolemic hyponatremia, euvolemic hyponatremia, or hypervolemic hyponatremia 2
- Assess serum osmolality, volume status, and urine osmolality and sodium level to determine the etiology of chronic hyponatremia 3
- Use point-of-care ultrasonography as an adjunct to physical assessment in estimation of volume status 4
- Consider additional tests, such as serum and urine electrolytes, to further classify the hyponatremia 5
Classification of Hyponatremia
Hyponatremia can be classified based on:
- Volume status: hypovolemic, euvolemic, or hypervolemic 2, 4
- Serum osmolality: hypotonic, isotonic, or hypertonic 5
- Urinary sodium concentration and osmolality: to further classify the hyponatremia 3, 5
Diagnostic Approach
The diagnostic approach to hyponatremia should involve:
- A rigorous approach to methodology and evaluation of evidence 6
- Consideration of patient-positive outcomes and provision of a useful tool for clinicians involved in everyday practice 6
- A systematic review of clinical practice guidelines and consensus statements to explore the scope, content, and consistency of these documents 5