Comparison of precision and sensitivity of the intracellular IFN-γ and the LDA assays.
Adequacy of a straight-line fit through the origin was examined for each of the assays. Two points determined the straight line—a value of the assay at the undiluted concentration and the origin. Data values for the intracellular IFN-γ assay were recorded at undiluted concentration levels and at titrations of 1:2, 1:4, 1:8, 1:16, and 1:160 of stimulated T cells. Data values for the LDA assay were recorded at the undiluted concentration, at 1:2 and 1:4 titration levels. To assess the closeness of the assay values to this straight line, the R2 statistic was used. AnR2 value of 1 resulted when the points fit exactly. Because the recorded assay value at the undiluted value was subject to variability, a range of R2values was computed to assess the sensitivity of theR2 statistic. (A) Results for the intracellular IFN-γ assay. Range of values at the undiluted values to create a straight line through the origin, 3220-3700. Coefficient of variation, 0.06. Range of R2 values, 0.968-0.979. (B) Results for the LDA assay. Range of values at the undiluted values to create a straight line through the origin, 1.7-11. Coefficient of variation, 0.6. Range ofR2 values, 0.0-0.96.
