Lipid Biochemistry USMLE Step 1 Practice Question
A 55-year-old man with metabolic syndrome and prior MI at age 48 presents with elevated apolipoprotein B (142 mg/dL) despite normal LDL cholesterol (110 mg/L). Vitals: BP 148/92, HR 88, RR 16, Temp 37°C, SpO2 98%. Labs reveal elevated triglycerides (280 mg/dL), normal glucose, and reduced HDL (32 mg/dL). He takes atorvastatin. Which mechanism best explains the discordance between LDL-C and apoB levels?
Answer choices
- ALaboratory error in apoB measurement with falsely elevated results
- BElevated lipoprotein(a) with excess apolipoprotein(a) but reduced apoB content
- CPresence of small, dense LDL particles carrying less cholesterol per particle but increased particle numberCorrect answer
- DGenetic polymorphism in apoB causing increased protein synthesis without lipid changes
- EHigh VLDL levels increasing apoB content independent of cholesterol concentration
- FIncreased hepatic synthesis of apoB100-containing VLDL remnants with preferential cholesterol ester transfer to HDL
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