COMPARISON OF LIPOPROTEIN(A) ASSAY-METHODS IN SERUM AND IN A PLASMINOGEN-FREE FRACTION

We compared five immunoassays for lipoprotein(a) (Lp(a)) determination (end-point immunonephelometry, two-site IRMA and three different ELIS A methods) in order to verify their agreement. Since it has been demon strated that human apo(a) structure is closely similar to that of plas minogen, cross-reactivity of apo(a) antibodies with plasminogen repres ents an important technical problem in serum Lp(a) quantification. On this account we used a plasminogen-free fraction obtained by one-step ultracentrifugation at a density of 1.125 g/ml, in which no plasminoge n activity was found. A satisfactory correlation between serum and pla sminogen-free fraction Lp(a) values was found for all the methods: the limits of agreement were too high, however, to use serum and fraction interchangeably. Furthermore, it emerged that the different assays we re more comparable and individual Lp(a) differences between methods we re less spread when plasminogen-free fraction was used instead of seru m.