Variability of exhaled breath condensate leukotriene B(4) and 8-isoprostane in COPD patients

The reproducibility of exhaled breath condensate (EBC) mediators is not well documented in chronic obstructive pulmonary disease (COPD). This study assessed within assay (WA), within (WD) and between day (BD) reproducibility of EBC leukotriene B(4) (LTB(4)) and 8-isoprostane. Three EBC samples were collected from 24 COPD patients separated by 1 h and 1 wk, to assess WD and BD reproducibility. WA reproducibility was assessed by sample analysis by enzyme immunoassay in triplicate. WA coefficient of variation for LTB(4) and 8-isoprostane (18.2% and 29.2%, respectively) was lower than corresponding values for WD (47.7% and 65.3%, respectively) and BD (75.7% and 79.1%, respectively). Repeatability coefficient for 8-isoprostane and LTB(4) assays were 18.6 pg/ml and 13.2 pg/ml, respectively. Group mean differences for WD and BD were small and statistically nonsignificant. Using the Bland Altman method, there were wide limits of agreement for WD (−51.6 to 47.2 for 8-isoprostane and −31.8 to 31.4 for LTB(4)) and BD reproducibility (−61.4 to 75.7 for 8-isoprostane and −29.3 to 38.6 for LTB(4)). This is the first study to fully report the variability of EBC 8-isoprostane and LTB(4) in COPD. WA variability and group mean changes were small. However, we observed considerable WD and BD variability for these biomarkers.