In HDL-C measurement using precipitation or immunoassay capture, which component is targeted for removal or binding?

• A. Apo-B containing lipoproteins
• B. HDL particles
• C. Apolipoprotein A-I only
• D. Chylomicrons

Answer: (A)

HDL-C measurements rely on isolating the HDL fraction by removing all non-HDL lipoproteins. In precipitation methods, reagents cause apoB-containing lipoproteins—LDL, VLDL, IDL, and chylomicron remnants—to precipitate out, leaving HDL in the solution to be measured. In immunoassay capture approaches, strategies are used to bind or remove the particles that carry ApoB, effectively separating them from HDL so the assay signal reflects HDL cholesterol. ApoB-containing lipoproteins define the non-HDL fraction, so targeting them for removal or binding is what allows HDL-specific measurement. HDL particles themselves contain ApoA-I, not ApoB, which is why removing ApoB-containing lipoproteins is the key step.