IMMUNOLUMINOMETRIC ASSAYS FOR THE QUANTIFICATION OF APOLIPOPROTEIN-A-I, APOLIPOPROTEIN-B, APOLIPOPROTEIN-C-II, APOLIPOPROTEIN(A) AND LIPOPROTEIN(A)

Immunoluminometric assays were developed for apolipoproteins A-I, B, C -II (as the apolipoprotein C-II: apolipoprotein B complex), apolipopro tein(a) and lipoprotein(a). The assays were evaluated clinically and m ethodologically. The results for apolipoprotein A-I, apolipoprotein B and lipoprotein(a) were compared with those obtained by turbidimetric assays. No comparison was possible for apolipoprotein C-II. Sample pre dilution was necessary for apolipoprotein A-I, apolipoprotein B, apoli poprotein(a) and lipoprotein(a). Not all antibody combinations gave ri se to assays with acceptable recovery rates. This was especially the c ase for lipoprotein(a). These assays for apolipoprotein(a) and lipopro tein(a) had relatively low detection limit (< 5 mg/1) and measuring ra nges up to 800 mg/l (using a 1: 10 sample dilution), and were suitable for routine use, especially for longer series. Assay times were all l ess than 3 h, each assay using the streptavidin-biotin technique and b eing based on a coated-ball technology. The median intra-assay coeffic ients of variation for all assays lay between 2.9 and 5.9% in the rang e of interest, expressed in terms of precision profiles. Inter-assay ( im)precision lay between 6.2 and 12.2%, calculated in the accepted way . Correlations between turbidimetric and immunoluminometric assays for apolipoprotein A-I and apolipoprotein B were statistically acceptable , although the correlation coefficients were mediocre (apolipoprotein A-I - r = 0.65, apolipoprotein B - r = 0.83) and the slope of the regr ession line differed from unity. This was most probably due to standar disation and differences in assay design (one-site competitive versus two-site immunometric assays). The correlation between the turbidimetr ic and immunoluminometric assays for lipoprotein(a) (r = 0.87) and apo lipoprotein(a) (r = 0.89) were good, although again, the slope of the regression line differed from unity, which was probably not due to fre e apolipoprotein(a) but to serum matrix effects, as the same standard was used in both assays. The assays were suitable for routine use, esp ecially when longer series were run. The costs were considerably lower than those for turbidimetric determinations. The high dilution factor for apolipoprotein A-I (up to 1 : 2000) and apolipoprotein B (up to 1 : 1000) could be seen as a disadvantage of the immunoluminometric ass ays.