Figure 3.
Top panels: distribution of TgAb concentrations found for the 607 sequential DTC sera (group C) received for routine Tg + TgAb testing. Method K (left panel) and method R (right panel) data are analyzed as subgroups with cutoff values covering the range from low to very high values, with focus on the LOD, FS, MCO, and ROC curve cutoffs. Bottom panels: method K (left panel) and method R (right panel) data for the 1426 group B DTC sera with TgRIA of ≥1.0 μg/L (n = 1426). The black bars show the group frequencies for false-negative misclassifications, expressed as a percentage of the total number of sera classified as “negative” by that cutoff. A false-negative TgAb classification was defined as a serum with a TgAb below the cutoff that had a Tg2GIMA/TgRIA ratio of <75%, suggesting the presence of interfering TgAb. The yellow bars show the group frequencies for false-positive misclassifications, expressed as a percentage of the total number of sera classified as “positive” by that cutoff. A false-positive TgAb misclassification was defined as a serum with a TgAb value more than or equal to the cutoff that had a Tg2GIMA/TgRIA ratio of ≥75%, suggesting the absence of interfering TgAb. The red bars show the frequencies for severe interference, defined as an undetectable Tg2GIMA (<0.10 μg/L) associated with an unequivocally detectable TgRIA (≥1.0 μg/L). Blue bars show the frequencies for sera with inappropriately low Tg2GIMA (<0.30 μg/L).