Automated latex nephelometric immunoassay for the measurement of serum lipoprotein (a)

Abstract

A sensitive immunoassay based on latex particle agglutination has been developed for measuring lipoprotein Lp(a) concentrations in serum or plasma. Carboxylated latex particles (diameter 240 nm) covalently coated with F(ab')2 fragments of anti-lipoprotein Lp(a) antibodies are incubated with diluted sample (400-fold) for 12 min at room temperature, with the resulting agglutination quantified by measuring the change of light-scatter produced. The assay has been automated on the Behring nephelometer analyzer with a sampling rate of 150 samples/hour. This assay generates a standard curve in the range of 27 to 1750 mg/L, showing inter-assay precision of less than 8%. There were no interferences from plasminogen, bilirubin, Intralipid, haemoglobin, rheumatoid factor, and apolipoprotein B. No significant differences were observed when fresh and frozen samples were compared. Sample pretreatment with "Lipoclean" clearing agent and sample lyophilization decreased the agglutinating reaction. In two separate studies using 77 and 112 patient sera the Lp(a) values, determined by the latex nephelometric method, the Terumo Macra Lp(a) ELISA test, and the Pharmacia Apo(a) radioimmunoassay method, gave correlation coefficients of 0.948 and 0.974, respectively. Physiological lipoprotein (a) values were determined in a blood donor group, with the distribution of serum Lp(a) highly skewed, with a mean (SD) and median values of 213(236) mg/L and 116 mg/L, respectively. Concentrations of Lp(a) were found to be age- and sex-independent. This latex nephelometric procedure is a convenient method and an interesting alternative to other immunoassays for routine measurement of human lipoprotein (a).

Technical Note

“…These data indicate that the precision of the turbidimetric method is good and comparable with or better than those obtained by other lipoprotein(a) methods (10)(11)(12)(13)16). 1).…”

“…We stored samples at -30 °C because we have previously found no significant differences in the lipoprotein(a) concentratrions of fresh and frozen samples (16).…”

“…Its lipoprotein(a) concentration (0.900 g/1) was determined by a nephelometric method by repeated testing (five days, n = 10 each day) as described elsewhere (16). In addition, a pool of serum was used as a secondary standard.…”

“…We measured lipoprotein(a) in serum samples by a latex-enhanced nephelometric immunoassay as previously described (16). This method uses carboxylated latex particles covalently coated with purified F(ab') 2 fragments, the latter being derived from a rabbit IgG antibody against lipoprotein(a) obtained from Behring (Behringwerke AG, Marburg, Germany).…”

Lipoprotein (a) in Chronic Renal Failure Patients Undergoing Hemodialysis: Does It Have an Independent Role in the Development of Further Cardiovascular Complications?

“…apo-A-I and apo-B measurement was performed by immunoturbidimetric methods adapted on a Hitachi 704 with Tina-Quant reagents (Boehringer). Lp(a) was determined by an immunonephelometric latex agglutination method developed in our laboratory on a Behring nephelometer BNA (Behringwerke AG, Marburg, Germany) [3]. Statistical nor mality was assessed with the KolmogorovSmirnov test.…”