TABLE 3.

Example of the effect of serum dilution on avidity determinations

IgG concn (μg/ml) at:% Reduction in IgG concnaCalculated WAbSerum dilution testedc
0 M NaSCN0.15 M NaSCN
13.8811.9813.70.661/100
13.929.7929.70.501/200
11.978.0632.70.481/400
10.005.8641.50.391/800
  • a Calculated as (IgG concentration at 0 M NaSCN − IgG concentration at 0.15 M NaSCN)/(IgG concentration at 0 M NaSCN) × 100. The elution method was used to calculate the IgG concentration (expressed in μg/ml) in the presence of 0.15 M NaSCN.

  • b Calculated as 0.79 + (−0.00963 × percent reduction in IgG concentration [μg/ml]).

  • c A single serum sample (serum 306B) is given as an example of the effect that serum dilution can have on avidity assay determinations. The overall CV in the calculated WA for this serum across dilutions was 39.5%.