Particle counting immunoassay for urinary cotinine. Comparison with chromatography, enzyme-linked immunoassay and fluorescence polarization immunoassay

Urinary cotinine was measured according to its inhibitory activity on the a gglutination of cotinine-coated latex particles by anti-cotinine antibodies , the agglutination being measured by optical counting of the remaining non -agglutinated particles (particle counting, PaC). The detection limit was 0 .03 mu g/ml and the practical range extended from 0.03 to 3.9 mu g/ml. The correlation results of 320 urine samples with those of high pressure liquid chromatography, enzyme-linked (Coti-Tracq EIA, Serex Inc., Maywood, NJ, US A), and fluorescence polarization immunoassay (TDX instrument, Abbott, Abbo tt Park, IL, USA) were r = 0.90, r = 0.69, r = 0.87, respectively, whereas the correlation coefficients between the assays other than particle countin g ranged from 0.62 to 0.88. PaC does not require any separation step and ca n thus be easily automated.