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Cardiovascular Endocrinology

SUN-235 - Oh Na! That'S Fake: A Case of Lpx Syndrome Underlying Pseudohyponatremia

Sunday, June 14, 2026
9:00 AM - 4:00 PM CT
Location: ENDOExpo; Poster Floor
Disclosure(s):
William Tong, D.O., MPH: No financial relationships to disclose
Introduction
Lipoprotein X (LpX) is a lipoprotein elevated in patients with liver dysfunction due to intrahepatic or extrahepatic cholestasis. LpX is not involved in normal cholesterol synthesis and therefore lacks negative feedback inhibition, resulting in marked hypercholesterolemia. Because LpX has the same density as low-density lipoprotein (LDL), it can cause falsely elevated LDL measurements. Although non-atherogenic, LpX accumulation may lead to xanthomas, hyperviscosity syndrome, and thrombotic events. Prompt recognition of LpX syndrome is essential to differentiate it from classic hyperlipidemia and guide management.

Case Presentation
A 35-year-old Caucasian female with primary biliary cholangitis (PBC) listed for liver transplantation presented after outpatient labs revealed severe hyponatremia. She was hemodynamically stable and asymptomatic. Skin examination revealed excoriations of the upper and lower extremities consistent with severe pruritus. ICU and Endocrinology were consulted.

The patient had been followed by the liver transplant clinic and had undergone cholecystectomy two years prior. Liver biopsy demonstrated PBC. MRCP showed a normal biliary tree without dilation or strictures.

Admission labs revealed sodium 115 mmol/L, potassium 3.3 mmol/L, bicarbonate 22 mmol/L, total bilirubin 11.3 mg/dL, alkaline phosphatase 1,716 U/L, AST 186 U/L, ALT 221 U/L, and GGT 748 U/L. Lipid panel demonstrated total cholesterol 1,616 mg/dL, triglycerides 206 mg/dL, HDL 6 mg/dL, and LDL 1,568 mg/dL. IgG was elevated at 3,129.9 mg/dL. Serum osmolality was elevated at 300 mOsm/kg, while arterial blood gas (ABG) showed sodium 140 mmol/L, confirming pseudohyponatremia. LpX was detected, and LDL cholesterol could not be accurately quantitated.

The patient was managed on the medical floor and stabilized for outpatient follow-up with transplant surgery for definitive treatment of PBC-associated LpX syndrome.

Discussion
This case underscores the importance of careful clinical judgment to prevent inappropriate escalation of care. Despite severe hyponatremia on routine testing, elevated serum osmolality and normal ABG sodium confirmed pseudohyponatremia. Recognition of LpX prevented initiation of statin therapy, which is ineffective and potentially harmful in cholestatic liver disease. Understanding the non-atherogenic nature of LpX guided management toward the underlying hepatobiliary pathology, avoiding unnecessary MICU admission and harmful interventions.

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