Lipoprotein X: artifactual lipid derangement in type 3c diabetes with obstructive liver disease

Lipoprotein X is an abnormal lipoprotein formed in cholestatic liver disease that causes artifactual elevation of calculated and measured direct low-density lipoprotein cholesterol (LDL-C). A 40-year-old man with chronic pancreatitis presented with hyperglycemic hyperosmolar state secondary to type 3c diabetes. He was jaundiced, with total bilirubin of 9.4 mg/dL (SI: 161 µmol/L) (reference range, 0.3-1.4 mg/dL [SI: 5-24 µmol/L]). Abdominal computed tomography showed severe common bile duct stricturing causing obstructive cholestasis. Laboratory results revealed a physiologically implausible lipid profile: total cholesterol (TC) of 1531 mg/dL (SI: 39.6 mmol/L) (desirable concentration, <200 mg/dL [SI: <5.2 mmol/L]) and direct LDL-C of 1636 mg/dL (SI: 42.3 mmol/L) (desirable concentration, <100 mg/dL [SI: <2.6 mmol/L]). Low-density lipoprotein cholesterol exceeding TC indicated analytical interference. Apolipoprotein B (ApoB) was elevated: 278 mg/dL (SI: 2.78 g/L) (reference range, 66-144 mg/dL [SI: 0.66-1.44 g/L]). The TC:ApoB ratio was 6.9 mmol/g (reference range, 3.8-6.3 mmol/g), supporting coexistent ApoB-negative lipoprotein. Liver and lipid parameters improved post-biliary stenting. ApoB normalized at 6 weeks, supporting a transient, insulin-deficiency-related ApoB-containing lipoprotein excess. Clinicians should suspect lipoprotein X when LDL-C exceeds TC in the setting of cholestasis; if ApoB is also elevated, transient ApoB-mediated dyslipidemia may coexist. Management centers on correcting underlying biliary and metabolic pathology.