Validation of IgE in Induced Sputum

Background and objectives: Soluble components are increasingly analyzed in induced sputum supernatant. However, only a few studies have measured total or specifi c immunoglobulin (Ig) E in sputum and none have attempted to validate it. We aim to validate laboratory measurements of total and specifi c IgE in induced sputum supernatant and to evaluate the infl uence of sputum processing with dithiothreitol (DTT) on IgE measurements. Methods: Total and specifi c IgE were measured by ImmunoCAP and the process was validated using sputum spiking experiments with total and specifi c IgE (to Dermatophagoides pteronyssinus and Phleum pratense) over a range of concentrations according to international recommendations. The Wilcoxon signed-ranks test was used for within-group comparisons and intraclass correlation coeffi cients were used to evaluate agreement between measurements. Two-tailed P values lower than .05 were considered signifi cant. Results: Samples from 18 patients (13 with interstitial lung disease, 2 with allergic asthma, and 3 healthy controls; 12 men; mean [SD] age, 45.6 [15.8] years) were evaluated. Median total IgE was 5.4 kU/L (interquartile range, 4.0-6.0 kU/L). Specifi c IgE levels to D pteronyssinus and P pratense were below 0.35 kUA/L in all samples. Recovery rates were above 80% for total and specifi c IgE over a wide range of values. No differences were found in total IgE measurements of sputum dispersed with DTT or phosphate-buffered saline, with a good intraclass correlation coeffi cient between both measurements (0.81, P=.01). Conclusions: Total and specifi c IgE measurements performed in induced sputum with a commercially available immunoassay are valid over a wide range of IgE levels.