Validation of total and specific IgE measurements in induced sputum

Soluble components are increasingly analyzed in induced sputum supernatant. However, only a few studies have measured total or specific immunoglobulin (Ig) E in sputum and none have attempted to validate it. We aim to validate laboratory measurements of total and specific IgE in induced sputum supernatant and to evaluate the influence of sputum processing with dithiothreitol (DTT) on IgE measurements.

Total and specific IgE were measured by ImmunoCAP and the process was validated using sputum spiking experiments with total and specific 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 coefficients were used to evaluate agreement between measurements. Two-tailed P values lower than .05 were considered significant.

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). Specific 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 specific 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 coefficient between both measurements (0.81, P=.01).

Total and specific IgE measurements performed in induced sputum with a commercially available immunoassay are valid over a wide range of IgE levels.