Dextran sulfate complexes with potasium phosphate to interfere in determinations of high-density lipoprotein cholesterol.

Abstract

The interference of dextran sulfate with the colorimetric determination of free cholesterol causes an increase in the absorbance that is proportional to the dextran sulfate concentration in the sample. This makes estimation of the free cholesterol concentration unreliable in high-density lipoprotein-containing supemates obtained after plasma precipitation with dextran sulfate/MgCl2 • Analysis of the absorption spectrum demonstrated that the absorbance increase was due to turbidity. We observed this effect with colorimetric reagents based on potassium phosphate buffer but not with those based on sodium phosphate or Tris buffers. This effect is ascribed to dextran sulfate because neither the omission of Mg2+ ions nor their chelation with EDTA prevented turbidity, whereas precipitation of dextran sulfate with Ba2+ counteracted this effect. Therefore, potassium phosphate-buffered reagents appear unsuitable for colorimetric lipid determinations in samples containing dextran sulfate.