Multiple lipoprotein and electrolyte laboratory artifacts caused by lipoprotein X in obstructive biliary cholestasis secondary to pancreatic cancer

Abstract

Lipoprotein X (Lp-X) is an abnormal lipoprotein which may form in patients with intra- and extra-hepatic cholestasis. The presence of very high levels of Lp-X has been shown to be a rare cause of pseudohyponatremia. We present a patient with severe obstructive cholestasis secondary to pancreatic cancer leading to very high Lp-X concentrations resulting in pseudohyponatremia, pseudohypokalemia, pseudohypochloremia and interference with the selective micellary solubilization direct low density lipoprotein cholesterol assay. These spurious laboratory anomalies impeded the initial clinical management of the patient including the attempted correction of the electrolyte abnormalities. After relief of obstruction following biliary stent placement, the patient's lipid levels normalized. Clinicians must be wary of laboratory artifacts and remember to correlate the laboratory values with the clinical presentation of the patient. Assays employing direct ion-selective electrodes such as those in blood gas analyzers are not subject to the interference of high concentrations of lipids or proteins, and maybe useful in situations where such interference is suspected. Furthermore the Vertical Auto Profile (VAP®) ultracentrifugation assay may be useful to detect lipoprotein X and low density lipoprotein cholesterol levels when the selective micellary solubilization technique fails to detect or quantify these lipid moieties.