For example, we know that for the curve fitting instead of the logistic function
For example, we know that for the curve fitting instead of the logistic function. The avidity of B19 IgG was measured with the recombinant VP1 antigen EIA (17), and the avidity of toxoplasma IgG was measured with the IgG Avidity Kit (Labsystems). Titration curves were drawn (i) according to the reference method (8) with 4+4 dilutions per sample (i.e., one series of four dilutions washed with urea and another series of four dilutions washed without urea), (ii) from the same EIA data sets (4+4 dilutions per sample) with a curve-fitting software based on logistic functions (see below), (iii) with the same logistic model but with only 2+2 dilutions per sample, and (iv) from the same data sets with a log-log model. Avidity was calculated as the ratio of IgG titers: (titer with urea/titer without urea) 100. Logistic model. A curve-fitting Win-95 computer program was developed for reproduction of the shapes of IgG titration curves. The fitting curve was, in its basic form, a so-called logistic function, Propofol + ? was the logarithm of the dilution ratio. The to-be-fitted variables Propofol were given certain limits beforehand that were based on avidity calculations performed earlier in our laboratory. For example, we know that for the curve fitting instead of the logistic function. As above, was the Rabbit Polyclonal to PNN logarithm of the dilution ratio. RESULTS In Propofol the reference method, EIA absorbances were plotted against serum dilutions on a semilogarithmic scale, and the individual data points (4+4 dilutions per sample) were united by straight lines (Fig. ?(Fig.1A).1A). Under the same conditions with 4+4 serum dilutions, the logistic model produced curvilinear, or smooth, IgG titration curves, which often bypassed individual data points (Fig. ?(Fig.1B).1B). With 2+2 serum dilutions per sample, the same logistic model produced IgG titration curves that resembled those obtained with 4+4 serum dilutions (Fig. ?(Fig.1C)1C) but, at Propofol the curve ends, met their data points precisely. The log-log model displayed linear IgG titration curves when both axes were linear (Fig. Propofol ?(Fig.1D). 1D). Open in a separate window FIG. 1 End-point titration curves for CMV IgG avidity determinations. Views are as seen on the computer screen. In each curve pair, the upper one was obtained without urea and the lower one was obtained with urea. Calculations were done with the reference method and 4+4 data points (dilutions of serum) (A), with the logistic model and 4+4 data points (B) and 2+2 data points (C), and with the log-log model and 2+2 data points. This CMV IgG is of low avidity. PBST, phosphate-buffered saline containing 0.05% Tween 20. The logistic model operating with 2+2 dilutions per sample was tested with all the serum panels, and the results were compared with those obtained with the reference method (operating with 4+4 data points). Overall, the two methods showed excellent correlation; the correlation coefficients for all four viruses and the one protozoan were 0.94 (Fig. ?(Fig.2).2). Also illustrated are the domains (bordered by broken lines) in which the avidity values obtained could be allowed to move without a change in diagnosis. For the 1,000 samples studied, only once, in the parvovirus serum panel, was there disagreement between the two methods; the reference method produced a pathological value of low avidity (12%), whereas the 2+2 logistic method produced a nonpathological value of high avidity (26%). This single crossover was due to a deviant EIA data point caused by an apparent pipetting error; however, this error was well tolerated by the 4+4 logistic method, which produced a borderline-avidity result.