Pseudohyponatremia in Hypertriglyceridemia-Induced Acute Pancreatitis: A Tool for Diagnosis Rather Than Merely a Laboratory Error?

Pseudohyponatremia: Mechanism, Diagnosis, Clinical Associations and Management

Pseudohyponatremia remains a problem for clinical laboratories. In this study, we analyzed the mechanisms, diagnosis, clinical consequences, and conditions associated with pseudohyponatremia, and future developments for its elimination. The two methods involved assess the serum sodium concentration ([Na]_S) using sodium ion-specific electrodes: (a) a direct ion-specific electrode (ISE), and (b) an indirect ISE. A direct ISE does not require dilution of a sample prior to its measurement, whereas an indirect ISE needs pre-measurement sample dilution. [Na]_S measurements using an indirect ISE are influenced by abnormal concentrations of serum proteins or lipids. Pseudohyponatremia occurs when the [Na]_S is measured with an indirect ISE and the serum solid content concentrations are elevated, resulting in reciprocal depressions in serum water and [Na]_S values. Pseudonormonatremia or pseudohypernatremia are encountered in hypoproteinemic patients who have a decreased plasma solids content. Three mechanisms are responsible for pseudohyponatremia: (a) a reduction in the [Na]_S due to lower serum water and sodium concentrations, the electrolyte exclusion effect; (b) an increase in the measured sample's water concentration post-dilution to a greater extent when compared to normal serum, lowering the [Na] in this sample; (c) when serum hyperviscosity reduces serum delivery to the device that apportions serum and diluent. Patients with pseudohyponatremia and a normal [Na]_S do not develop water movement across cell membranes and clinical manifestations of hypotonic hyponatremia. Pseudohyponatremia does not require treatment to address the [Na]_S, making any inadvertent correction treatment potentially detrimental.

Mind the gap: A case of unexplained elevated anion gap without concomitant metabolic acidosis

Hypertriglyceridemia causing unexplained hypobicarbotinemia and elevated anion gap is rare. We report the case of a 33-year-old woman who presented with an unexplained high anion gap after a subacute gastrointestinal illness. An arterial blood gas showed a normal bicarbonate level, and a lipid panel resulted in a triglyceride level too high to read, establishing the diagnosis. Treatment included using triglyceride-lowering agents with normalization in the patient's serum bicarbonate levels.

Hypercholesterolemia due to lipoprotein-X manifesting as pseudohyponatremia in a patient with cholestasis

Pseudohyponatremia is an often misdiagnosed condition that needs to be managed by addressing the underlying cause. Treatment of hyponatremic patients with intravenous fluids without ruling out pseudohyponatremia may aggravate a patient's hyponatremia and result in adverse outcomes. In a patient whose sodium is deteriorating, it is critical to diagnose pseudohyponatremia early in the course and acquire necessary consultations, even if the patient is asymptomatic. We discuss a case of a man in his 20s with a history of liver transplantation who presented with unexplained dangerously low sodium while being asymptomatic. The case illustrates an uncommon cause of pseudohyponatremia due to lipoprotein-X hypercholesterolemia in a patient with cholestatic liver disease.

Pseudohyponatraemia caused by acute pancreatitis-derived hypertriglyceridaemia

We report a case of pseudohyponatraemia due to severe hypertriglyceridaemia-induced acute pancreatitis, stemming from unknown diabetes. A woman in her late 30s was admitted to the local hospital by her general practitioner due to severe hyponatraemia (116 mmol/L) and upper abdominal pain. At admission to the hospital, there was a discrepancy of 19 mmol/L between arterial and venous sodium, along with severe hypertriglyceridaemia and hypercholesterolaemia. Pancreatitis was diagnosed using a CT scan. The patient received plasmapheresis which significantly reduced triglycerides, and venous plasma sodium was normalised indicating pseudohyponatraemia at admission. Finally, a haemoglobin A1c of 83 mmol/mol was found. Diabetes was diagnosed, and insulin was initiated.