What density and duration are used in ultracentrifugation for HDL-C isolation?

• A. 1.063 g/mL for 24 hours
• B. 1.21 g/mL for 6 hours
• C. 1.063 g/mL for 2 hours
• D. 1.17 g/mL for 12 hours

Answer: (A)

Density-based separation is the key idea. Lipoproteins have characteristic densities, with HDL occupying the higher end of the spectrum (roughly 1.063 to 1.21 g/mL). In isopycnic ultracentrifugation, adjusting the sample to a density of 1.063 g/mL allows the less dense lipoproteins (chylomicrons, VLDL, and LDL up to about 1.063) to move out of the HDL-rich zone, so the HDL-containing fraction can be collected. A long spin, around 24 hours, ensures complete migration to the isopycnic positions and clean separation between HDL and the other lipoproteins. Shorter durations or different densities can leave overlapping fractions and produce less pure HDL.