An assay pad for measuring the concentration of HDL-associated cholesterol in a sample, a method for using the pad, and a diagnostic assay device for carrying out the method are described. The assay pad includes a polymer adhesive or heat laminate bond. The assay design prevents interference by reagents used for such removal with the HDL quantification reaction or with other assays carried out on the same sample. If desired, removal of non-HDL lipoproteins and assay of HDL cholesterol can be carried out without interruption of the assay.