[Multicenter evaluation on different analyzers of three methods for direct HDL-cholesterol assay]

Most frequently, in routine laboratories, C-HDL is measured in the supernatant after precipitation of apolipoprotein B-containing lipoproteins by the sodium phosphotungstate/magnesium chloride reagent (PTA). This method involves precipitation, centrifugation and decantation steps which prevent full automation of the measurement and decrease the accuracy of the results. Recently, three direct assays for C-HDL including alpha-cyclodextrin sulphate (alpha-CD), polyanions/detergents (PA-D) or antibodies anti-beta-lipoproteins (AC) have been commercialized, in which all steps are fully managed by automated analyzers. These new methods have been compared to the conventional procedure (PTA), in multicenter studies among six laboratories using different analyzers. The C-HDL values measured by the alpha-CD and PA-D assays correlated well with those of the PTA method (r > 0.98), on most of the analyzers. With the AC assay, only the results obtained with the Hitachi 717 analyzer were correlated with C-HDL values of the PTA method. The linearity and specificity studies were evaluated in the laboratory A on a Kone Specific analyzer. The alpha-CD and PA-D assays were linear for C-HDL values from 0 to 5.56 mmol/l, as observed by increasing amounts of HDL2 + HDL3 or serum without lipoprotein isolated by ultracentrifugation. The specificity of these two methods was evaluated simultaneously, by adding various amounts of lipoproteins isolated by sequential ultracentrifugation. No interference was observed when adding chylomicrons up to 13.4 mmol/l of triglycerides for both methods. Inversely, increased C-HDL values were observed with added VLDL from 6 mmol/l of triglycerides for the PA-D assay and from 8 mmol/l for the alpha-CD assay. No interference was observed with added LDL up to 11.5 mmol/l of C-LDL for the alpha-CD assay and up to 6.7 mmol/l for the PA-D assay. In conclusion, the present multicenter evaluation demonstrates that the new procedures for the direct automation of C-HDL are easy and accurate and most of them correlated well with the classical precipitation method. In addition the study provides arguments for a choice between the different direct C-HDL methods.