Name a commonly used precipitating reagent to separate HDL cholesterol from other lipoprotein cholesterol fractions.

Name a commonly used precipitating reagent to separate HDL cholesterol from other lipoprotein cholesterol fractions.

• A. Zinc sulfate
• B. Trichloroacetic acid
• C. Heparin-manganese
• D. Isopropanol

Answer: (C)

The concept being tested is how to selectively isolate HDL by precipitating the other lipoproteins. In HDL cholesterol assays, you want to remove the apoB-containing particles (LDL and VLDL) so that only HDL remains in the solution for measurement. Heparin combined with manganese ions does exactly that: it forms a complex that precipitates the apoB-containing lipoproteins, leaving HDL in the supernatant. After removing the precipitate, the cholesterol in the HDL fraction can be measured directly. Other reagents listed aren’t used for this selective HDL precipitation in standard assays. Zinc sulfate, trichloroacetic acid, and isopropanol don’t provide the same selective precipitation of apoB-containing lipoproteins that preserves HDL in solution, so they’re not the preferred reagents for isolating HDL before cholesterol measurement.

The concept being tested is how to selectively isolate HDL by precipitating the other lipoproteins. In HDL cholesterol assays, you want to remove the apoB-containing particles (LDL and VLDL) so that only HDL remains in the solution for measurement. Heparin combined with manganese ions does exactly that: it forms a complex that precipitates the apoB-containing lipoproteins, leaving HDL in the supernatant. After removing the precipitate, the cholesterol in the HDL fraction can be measured directly.

Other reagents listed aren’t used for this selective HDL precipitation in standard assays. Zinc sulfate, trichloroacetic acid, and isopropanol don’t provide the same selective precipitation of apoB-containing lipoproteins that preserves HDL in solution, so they’re not the preferred reagents for isolating HDL before cholesterol measurement.