Comparison of a new immunoturbidometric assay of human serum lipoprotein (a) to the ELISA and the IRMA methods

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Abstract
In the present work we have tested a new immunoturbidometric (IT) lipoprotein(a) (Lp(a)) assay and compared it with two other Lp(a) assay systems (IRMA and ELISA) commonly used in clinical chemistry laboratories. In addition, we have examined the effects of long-term storage and plasminogen on the results of Lp(a). Intra-assay and inter-assay coefficients of variation of the IT method were from 1.6 to 5.5% and from 2.8 to 10.7% depending on the concentration of Lp(a). The correlations between methods were 0.957 (IRMA vs. IT), 0.969 (IRMA vs. ELISA) and 0.956 (IT vs. ELISA) and the regression curves were IRMA = 1.07*IT + 11, IRMA = 1.84*ELISA + 2 and IT = 1.62*ELISA + 17, respectively. Storage of the samples for 5 years at — 70°C did not affect serum Lp(a) levels. There was a slight increasing effect of high concentrations of plasminogen on the Lp(a) results, but on physiological serum levels of plasminogen the effect was not significant. We conclude that the IT method provides a simple way to screen serum Lp(a) levels.