Misleading results in cases of coexisting acetaminophen and salicylate overdose.

To the Editor: we had both pools evaluated at another laboratory by a continuous-flow (AutoAnalyzer II) method involving the Liebermann-Burchard determination of cholesterol after M&2-Hep (92mmol Mn2 per liter) precipitation of lipoproteins (3, 6). Values obtained for HDL-C in serum with Mg24-Phos, Isopol, and MnS+Hep, by use of the one enzymic procedure on the KDA, all exhibited significant positive bias as compared to the Liebermann-Burchard (AutoAnalyzerll) method (Table 1). For both serum and plasma, the MnS+Hep enzymically determined HDL-C reflected strong positive and variable interference relative to the LiebermannBurchard (AutoAnalyzer II) method (Table I). Similar positive interference was noted by Steele et al. (7) and Liedtke et a!. (8), using enzymic determination of HDL-C and Mn2-Hep precipitation of liproproteins. We were not able to correct for this interference by including ethylenediammnetetraacetate in the KDA reagent diluent. The PEG procedure yielded serum HDL-C valuesclosestto those obtained with the comparison procedure; the Mg2+Phos procedure gave values closest to those for plasma HDL-C by the comparison procedure. Differences among results after various methods of precipitation (Table 1) may reflect interference with the KDA enzymic method rather than real differences in HDL-C. The overall CV for percent HDL (electrophoresis) was quite high: 14%. This agrees with the data first reported by Cobb and Sanders (9) but disagrees with a later report by Gamblin (10), who quoted CV’s of about 5 and 3%. The CV for our densitometer scanning was 4%. Patient evaluation. Using Mg2-Phos and PEG, we compared HDL-C of 25 patients’ serum samples. The Mg2+ Phos procedure yielded significantly higher results, averaging 19 mg/L higher (p <0.01, r = 0.95). We favor the PEG procedure for use with the KDA. Variable interferences were encountered with most of the methods tested and clinical-decision values must be carefully determined.