Evaluation of interferences in rate and fixed-time nephelometric assays ofspecific serum proteins

We performed interference studies for IgG, IgA, IgM, haptoglobin, and alpha (1)-antitrypsin assayed in serum, using either fixed-time nephelometry on t he BN 100 from Behring or rate nephelometry on two analyzers from Beekman I nstruments. For clear serum samples, results for IgG, IgG, IgM, and haptogl obin obtained with the three nephelometers showed good agreement. Values fo r alpha(1)-antitrypsin in clear sera were lower with the BN 100 than with t he Array 360 or Immage. In lipemic samples, the BN 100 gave higher values t han the Array 360 or Immage for all analytes except IgG. Addition of Intral ipid to serum produced atypical reactions with the BN 100 (fixed-time nephe lometry) but not with the Array 360 or Immage (rate nephelometry). The inte rference of lipemia on the BN 100 was also seen when the Beekman antibody w as used, indicating that the effect was reagent-independent. For hemolyzed samples, the BN 100 gave higher values than the Array 360 or Immage for hap toglobin but not for the other analytes, Addition of increasing amounts of a hemolysate to serum revealed a negative interference in all assay systems . This effect was more pronounced with the Beekman reagent than with the Be hring reagent in all three nephelometers and was independent of the type of instrument (fixed-time vs rate nephelometry).