Automated Turbidimetry of Serum Lipoprotein(a)

We describe a simple iminunoturbidimetric method for quantifying lipoprotein(a) in serum based on latex-enhanced particle agglutination technology. Carboxylated latex particles (diameter 240 nm) covalently coated with F(ab')2 fragments of anti-lipoprotein(a) antibodies are incubated with the sample for 5 min at 37°C, and the resulting agglutination is quantified by measuring the change of turbidity produced at 700 nm. The assay is rapid, precise and fully automated on the Hitachi 911 analyser. The assay range is about 0.03—0.9 g/l. Average analytical recovery was 97.8%. Precision (CV) ranged from 1.9 to 3.1% at different lipoprotein(a) values. There was no interference from bilirubin, Intfalipid®, haemoglobin, plasminogen or apolipoprotein B. Comparisons with a latex nephelometric assay carried out on the Behring nephelometer analyser, and with three commercially available methods, a radioimmunoassay and two ELISA assays, gave good correlations (r > 0.95), although a large among-method variation in lipoprotein(a) values was found. We conclude that the proposed latex turbidimetric immunoassay method is suitable for routine use in clinical laboratories.