A51-57 When Sodium Lies: Pseudohyponatremia in Severe Hyperbilirubinemia

Abstract Introduction Hyponatremia is the most commonly diagnosed electrolyte disturbance in hospitalized patients. While difficult to quantify, one study has shown that around 17% of cases initially diagnosed as hyponatremia may actually be pseudohyponatremia when confirmed with direct measurement. Misdiagnosis and inappropriate treatment can lead to very serious consequences, including seizures, permanent neurological injury, and even death. Determining the underlying etiology of hyponatremia is often challenging, but is critically important. We present a case of pseudohyponatremia, caused by elevated levels of lipoprotein X from hyperbilirubinemia. Case A 33 year old male with past medical history of necrotizing pancreatitis, hypertriglyceridemia, biliary stricture post biliary stent placement, and diabetes mellitus presented to the emergency room for two weeks of nausea, vomiting, and abdominal pain, found to be in euglycemic diabetic ketoacidosis (DKA). Initial labs revealed a sodium level of 115 mmol/L, triglycerides of 800 mg/dL, and total bilirubin of 8.2 mg/dL.His hyponatremia was initially thought to be hypovolemic hyponatremia from recent nausea and vomiting, and his hyperbilirubinemia was thought to be from biliary stent blockage. His sodium levels did not change much after receiving fluids via DKA protocol. The patient remained neurologically intact, and his gastrointestinal symptoms gradually resolved; thus, his hyponatremia was considered asymptomatic. Endocrinology recommended a slow bolus of 250 mL 3% saline, but his sodium levels remained under 118 mmol/L after two such boluses. Triglyceride levels were fluctuating between 200 and 800 mg/dL while on the insulin drip; interestingly sodium levels did not follow the same pattern. Sodium level on venous blood gas was 137 mmol/L, and LDL was elevated at 1960 mg/dL. Serum osmolality was within normal limits, consistent with pseudohyponatremia. He ultimately was diagnosed with pseudohyponatremia, likely from elevated levels of lipoprotein X from hyperbilirubinemia. Discussion While the most common causes of pseudohyponatremia are hypertriglyceridemia and paraproteinemia, elevated levels of other lipids can also be a cause. Obstructive jaundice can cause profound hyperlipidemia, from accumulation of high levels of lipoprotein X, an abnormal phospholipid-rich lipoprotein. Most basic metabolic panels indirectly measure sodium levels. Lipoprotein X interferes with these sodium measurements by displacing the water from the blood samples and causing refractory errors. Blood gas analysis directly measures sodium levels, providing a more accurate measurement in cases such as this. We believe in patients presenting with hyponatremia in the appropriate clinical context, serum osmolality, a full lipid panel, and blood gas electrolytes should be assessed upon presentation. This abstract is funded by: None