High-density-lipoprotein cholesterol in heparin-MnCl2 supernates determined with the Dow enzymic method after precipitation of Mn2+ with HCO3-.

Manganese interferes with enzymic cholesterol methods. In this study, we enzymically measured high-density-lipoprotein (HDL) cholesterol in heparin-Mn2+ supernates that had been treated with NaHCO3 (91 mmol/L) to precipitate Mn2+, and compared results with those by an automated Liebermann- Burchard method. For untreated supernates of 96 fresh plasma samples, the enzymic values were 10.4% higher than comparison-method values, a bias that declined to +2.3% for treated supernates. For 72 sera promptly frozen and stored after collection, the enzymic values for untreated and treated supernates were, respectively, 6.0% and 0.5% higher than comparison-method values. In all cases, the magnitude of the bias was independent of the concentrations of cholesterol, triglyceride, and HDL-cholesterol. Enzymic HDL-cholesterol measurements in NaHCO3-treated heparin-Mn2+ supernates prepared from four pooled serum controls agreed within 21 mg/L with values established for these pools by the Centers for Disease Control. We conclude that the accuracy of enzymic HDL cholesterol measurements in heparin-Mn2+ supernates in considerably increased by treatment with NaHCO3.