What are the diagnostic testing differences for hyponatremia in Beer Potomania (Potomania associated with beer consumption) versus Cirrhosis versus Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) versus Hypovolemic Hyponatremia?

From the Guidelines

Diagnostic testing for hyponatremia should prioritize a systematic approach to differentiate between beer potomania, cirrhosis, SIADH, and hypovolemic hyponatremia, with a focus on serum and urine osmolality, urine sodium, and volume status assessment, as recommended by the 2021 practice guidance by the American Association for the Study of Liver Diseases 1. To differentiate between these conditions, the following diagnostic tests and assessments are essential:

• Serum and urine osmolality
• Urine sodium
• Volume status assessment
• Liver function tests to identify signs of liver dysfunction, such as elevated liver enzymes, elevated bilirubin, and decreased albumin, which are characteristic of cirrhotic hyponatremia
• Thyroid and adrenal function tests to rule out underlying endocrine disorders that may contribute to SIADH
• Medication review to identify potential causes of SIADH In beer potomania, expect low serum osmolality (<280 mOsm/kg), low urine sodium (<20 mEq/L), and normal to increased volume status due to excessive beer intake with poor solute intake. Cirrhotic hyponatremia presents with low serum osmolality, low urine sodium, ascites, and signs of liver dysfunction, as noted in the 2018 clinical practice guidelines for liver cirrhosis 1. SIADH shows low serum osmolality, inappropriately elevated urine osmolality (>100 mOsm/kg), high urine sodium (>40 mEq/L), and euvolemic status without edema or ascites; thyroid and adrenal function tests should be normal. Hypovolemic hyponatremia presents with clinical dehydration, low serum osmolality, high urine osmolality, and variable urine sodium depending on the cause (low in GI losses, high in renal losses). The pattern of laboratory findings combined with clinical presentation will guide the differential diagnosis and appropriate management strategy, with treatment depending on the etiology, chronicity, severity, and urgency of hyponatremia, as outlined in the 2021 practice guidance by the American Association for the Study of Liver Diseases 1. Key considerations in management include:
• Fluid restriction for hypervolemic hyponatremia, as recommended in the 2010 EASL clinical practice guidelines on the management of ascites, spontaneous bacterial peritonitis, and hepatorenal syndrome in cirrhosis 1
• Administration of hyperoncotic albumin and/or vasopressin receptor antagonists ("vaptans") for hypervolemic hyponatremia, as noted in the 2021 practice guidance by the American Association for the Study of Liver Diseases 1
• Discontinuation of diuretics and/or laxatives and provision of fluid resuscitation for hypovolemic hyponatremia, as recommended in the 2021 practice guidance by the American Association for the Study of Liver Diseases 1.

From the Research

Diagnostic Testing for Hyponatremia

The diagnosis of hyponatremia involves evaluating the patient's fluid volume status, neurological symptoms, and the severity and duration of hyponatremia 2, 3. The following steps can be taken to diagnose the underlying cause of hyponatremia:

• Measure plasma osmolality, glucose, lipids, and proteins to differentiate between hypervasopressinemic and non-hypervasopressinemic hyponatremias 3
• Determine urine osmolality and assess extracellular fluid volume status 3
• Measure urine sodium concentration to provide further information for differential diagnosis 3

Differential Diagnosis of Hyponatremia

The differential diagnosis of hyponatremia includes:

• Hypovolemic hyponatremia: characterized by low extracellular fluid volume and low urine sodium concentration 2, 3
• Euvolemic hyponatremia: characterized by normal extracellular fluid volume and high urine sodium concentration; the syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a common cause of euvolemic hyponatremia 2, 3
• Hypervolemic hyponatremia: characterized by high extracellular fluid volume and low urine sodium concentration; cirrhosis is a common cause of hypervolemic hyponatremia 4
• Beer potomania: a rare cause of hyponatremia characterized by severe hyponatremia, hypokalemia, and dilute urine in patients who ingest large quantities of beer 5, 6

Diagnostic Features of Specific Causes of Hyponatremia

The following are some diagnostic features of specific causes of hyponatremia:

• Cirrhosis: characterized by ascites, portal hypertension, and activation of compensatory mechanisms such as the renin-angiotensin-aldosterone system (RAAS), sympathetic nervous system, and antidiuretic hormone (ADH) 4
• SIADH: characterized by low plasma osmolality, high urine osmolality, and elevated urine sodium concentration 3
• Beer potomania: characterized by severe hyponatremia, hypokalemia, and dilute urine in patients who ingest large quantities of beer; treatment with isotonic sodium chloride can rapidly correct the hyponatremia 5, 6