Abstract: Methods of making and using a stable diagnostic reagent for use in serological testing procedures, and in particular, non-auto-agglutinating polystyrene latex particles with surfaces containing a protein, substantially methylated serum albumin, and a bound, negatively-charged polymeric compound. The particles may be sensitized with a number of negatively-charged compounds, including proteins, polysaccharides and various cell nuclear components. When the coated latex particles are adsorbed with native deoxyribonucleic acid, the resultant immunological reagent can be used to detect certain autoimmune diseases, particularly serum lupus erythematosus.