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194) A patient with stage 4 cirrhosis, decreased synthetic function (low total protein, albumin, and coagulopathy) and hepatic encephalopathy is found to have a serum sodium level of 124 mEq/L (reference range, 135 to 145 mEq/L). Which one of the following is the most likely etiology for the patient’s hyponatremia?

Activation of the renin-aldosterone system. Overhydration. Assay interference by elevated bilirubin. Nutritional imbalance. Normal variation in serum sodium.

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• Patients with end-stage cirrhosis have severe ascites and third spacing caused by low plasma oncotic pressure. This depletes their intravascular volume, activating the renin-aldosterone system to preserve volume. As a result, electrolyte disturbances, including hyponatremia or hypernatremia, are common in this patient population.

• Overhydration is possible, but it is not the most common mechanism for electrolyte disturbances in patients with liver failure.

• Interference in the sodium assay by hyperbilirubinemia is possible, but it is not the most common mechanism for electrolyte disturbances in patients with liver failure.

• Nutritional imbalance very rarely causes hyponatremia.

• Serum sodium is very tightly regulated and is not subject to wide intraindividual variation.

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Clinical Pathology: General Principles, Lab Management, Clinical Chemistry, Microbiology, Immunology & Histocompatibility, Urinalysis, Body Fluids, Clinical Microscopy

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