Several prospective clinical trials and epidemiological studies have shown that a low concentration of high-density lipoprotein-cholesterol (HDL-C) is an independent risk factor for coronary heart disease (CHD).^1,2 It is estimated that for every 0.0259 mmol/l decrease in HDL-C, the relative risk of CHD events increases by 2–3%.³ Accordingly, HDL-C determinations are included in CHD prevention programmes.⁴ Reliable and easy to perform HDL-C assays are therefore required for routine laboratory practice.

There is often an inverse relationship between HDL-C and triglyceride concentrations. Accordingly, specimens with a low HDL-C often have a raised triglyceride concentration. HDL-C assay manufacturers often recommend dilution when the triglyceride is above a particular concentration. We decided to evaluate our routine HDL-C method to assess what triglyceride cut-off we should routinely utilise before specimen dilution.

HDL-C concentrations were determined using an anti human-β-lipoprotein antibody that binds to non-HDL lipoproteins and allows the quantification of HDL-C by the presence of a cholesterol esterase and cholesterol oxidase/peroxidase enzyme chromogen system (Olympus Life & Material Science Europa GmbH (Irish Branch)) on an Olympus AU600 analyser. Triglyceride was determined with a glycerolphosphate oxidase phenol-aminophenazone method (Olympus Life & Material Science Europa) on an Olympus AU600 analyser. Both assays were performed according to the manufacturer’s protocol. The manufacturer recommends that specimens are diluted with saline (no dilution factor stated) when the triglyceride concentration is >11.3 mmol/l. The …