The Case: Hyponatremia in a patient with obstructive jaundice

A 40-year-old man with a past medical history of autoimmune pancreatitis, lymphoplasmacytic sclerosing cholangitis, biliary stricture with stent placement, hyperlipidemia, and diabetes mellitus presented with fever for 2 days. Review of systems was negative for nausea, vomiting, poor oral intake, and diarrhea. He denied shortness of breath. Pertinent physical exam findings included fever, jaundice, icteric sclerae, moist oral mucosa, non-tender, non-distended abdomen, and absence of edema in lower extremities. No hepatomegaly was noted on exam.

Laboratory tests revealed a serum sodium of 119?mEq/l, potassium of 3.3?mEq/l, chloride of 87?mEq/l, and a serum osmolality of 297?mOsm/kg. Total cholesterol was 2109?mg/dl. His lipid panel, however, demonstrated a low-density lipoprotein level of 68?mg/dl, high-density lipoprotein level of 36?mg/dl, and triglycerides of 299?mg/dl. Electrolytes on a repeat blood sample were checked simultaneously using the indirect ion-selective electrode (ISE) method and the direct ISE method. These results are depicted in the table below.