Particle counting assay for anti-toxoplasma IgG antibodies. Comparison with four 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 remaining unagglutinated. The running time was 45 min. This test (PaC) was compared using 243 serum samples with four automated commercial immunoassays: the Enzymum test Toxo IgG (ES300, Boehringer), the Vidas Toxo IgG (Biomérieux), the IMX Toxo IgG (Abbott), the Magia Toxoplasma gondii 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, respectively), 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 PaC and Toxo IgG Boehringer, Biomérieux, 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 positive samples by PaC were found to be positive by enzyme-immunoassays except for eight sera which were doubtful positives by the Enzymum test ToxoIgG from Boehringer. No negative sample by PaC was found positive by any of the enzyme-immunoassays. In PaC, when two latex preparations coated with different antigen were compared, the correlation was rather weak (r = 0.93) suggesting that the selection of the antigen can be critical. In conclusion, the four automated commercial immunoassays now available gave similar results. However, the discrepancies observed in this study underlined the importance of clinical and biological follow-up of the patients and the necessity to confirm the result. The introduction of a new technique such as PaC, which is now available for a large variety of assays in Clinical Chemistry and Microbiology, is justified by its intrinsic advantage of homogeneity. Therefore, automation is easy as well as the control of possible interference.

Comparison of urinary excretion of albumin, alpha 1-microglobulin and retinol-binding protein in diabetic patients.

Small amounts of urinary proteins observed at early stages of diabetic nephropathy may result from both glomerular and proximal tubular dysfunction. However, the relative contribution of the two mechanisms remains controversial. We compared the urinary excretion of three low-molecular-weight proteins (albumin, alpha 1-microglobulin and retinal-binding protein) in 104 diabetic patients and 104 control subjects who had a plasma creatinine concentration of less than 130 mumol/l. Excretion of low-molecular-weight proteins was expressed as the ratio of protein to creatinine concentration. There were significant correlation (p < 0.01) between excretion of the three low-molecular-weight proteins measured in urine sample and 24-h urine collections in diabetic and control subjects. The concentrations of these proteins in single voided urinary samples and 24-h urine collections in diabetic patients were highly correlated. Excretion of retinal-binding protein, alpha 1-microglobulin and glucose in 24-h urine collections and of RBP and glucose in urinary samples was higher in diabetic than non-diabetic patients regardless of the type of diabetes and insulin-dependence. alpha 1-microglobulin and albumin excretions in urinary samples were significantly influenced by blood glucose control, as attested by the glycosylated haemoglobin level. Increased urinary excretion of alpha 1-microglobulin and retinol-binding protein reflected proximal tubular dysfunction in diabetic patients. However, only alpha 1-microglobulin correlated with the glycaemic control. It remains to be determined whether this protein could serve as an additional early marker of diabetic nephropathy.

Particle counting immunoassay for urinary cotinine. Comparison with chromatography, enzyme-linked immunoassay and fluorescence polarization immunoassay.

Urinary cotinine was measured according to its inhibitory activity on the agglutination of cotinine-coated latex particles by anti-cotinine antibodies, the agglutination being measured by optical counting of the remaining non-agglutinated particles (particle counting, PaC). The detection limit was 0.03 microgram/ml and the practical range extended from 0.03 to 3.9 micrograms/ml. The correlation results of 320 urine samples with those of high pressure liquid chromatography, enzyme-linked (Coti-Tracq EIA, Serex Inc., Maywood, NJ, USA), and fluorescence polarization immunoassay (TDX instrument, Abbott, Abbott Park, IL, USA) were r = 0.90, r = 0.69, r = 0.87, respectively, whereas the correlation coefficients between the assays other than particle counting ranged from 0.62 to 0.88. PaC does not require any separation step and can thus be easily automated.