PARTICLE COUNTING ASSAY FOR ANTITOXOPLASMA IGG ANTIBODIES - COMPARISON WITH 4 AUTOMATED COMMERCIAL ENZYME-LINKED IMMUNOASSAYS

An assay for anti-toxoplasma IgG antibodies based on agglutination of latex particles was set up and compared with commercial immunoassays. The reaction was measured by instrumental counting of particles remain ing unagglutinated, The running time was 45 min. This test (PaC) was c ompared using 243 serum samples with four automated commercial immunoa ssays: the Enzymum test(R) Toro IgG (ES300, Boehringer), the Vidas Tor o IgG (Biomerieux), the IMX Toro IgG (Abbott), the Magia Toxoplasma go ndii IgG (Merck). The mean values (+/- SD) obtained by IMX (25 IU +/- 68) and ES300 (45 IU +/- 142) were significantly lower than the values obtained by Vidas (73 IU +/- 237, p < 10(-4) and p = 0.006, respectiv ely), by Magia (80 IU +/- 300, p < 10(-4) and p = 0.0005) and by PaC ( 70 IU +/- 260, p < 10(-4) and p = 0.0126). The correlations between Pa C and Toro IgG Boehringer, Biomerieux, Abbott, Merck were r = 0.97, r = 0.98, r = 0.94, r = 0.98, respectively. The correlation coefficients between the enzyme-immunoassays ranged from 0.96 to 0.99. All positiv e samples by PaC were found to be positive by enzyme-immunoassays exce pt for eight sera which were doubtful positives by the Enzymum test To xoIgG from Boehringer. No negative sample by PaC was found positive by any of the enzyme-immunoassays. In PaC, when two latex preparations c oated with different antigen were compared, the correlation was rather weak (r = 0.93) suggesting that the selection of the antigen can be c ritical. In conclusion, the four automated commercial immunoassays now available gave similar results. However, the discrepancies observed i n this study underlined the importance of clinical and biological foll ow-up of the patients and the necessity to confirm the result. The int roduction of a new technique such as PaC, which is now available for a large variety of assays in Clinical Chemistry and Microbiology, is ju stified by its intrinsic advantage of homogeneity. Therefore, automati on is easy as well as the control of possible interference. (C) 1997 E lsevier Science B.V.