Multivariate models for concurrent outcomes and APE-associated predictions.

aData from study group 1, n = 56. We found no evidence of two-way interactions or non-linear effects using squared terms for these models. Age, gender, CF-related diabetes, airway infection with either Pseudomonas aeruginosa or Staphylococcus aureus and chronic azithromycin, oral or inhaled steroid use had no significant interactions with any inflammatory marker terms in any multivariate model. Log transformed values of biomarkers were used for modeling outcomes. Concurrent FEV1% and Weight-for-age z-score models used linear regression. The model for the number of APE occurring in the year prior to initial sputum collection used quasi-Poisson regression.
bData from study group 2, n = 26. Additional adjustment for the stable FEV1% measurement, sequence of stable and APE time point collections, airway infection with either Pseudomonas aeruginosa or Staphylococcus aureus, use of azithromycin or steroids had no significant effect in these models.
cEstimates of the mean change in FEV1% per unit change in log scale biomarkers. Results from a linear regression model for the associations between difference in FEV1% between stable and APE time points and GM-CSF (log scale) measured at the APE onset time point. Each univariate representing measurements obtained during clinically stable and APE time points were added in turn to a model containing GM-CSF measured at the APE time point, the only statistically significant univariate. IL-5 (p = 0.006) and IL-10 (p = 0.015) measured at the APE time point and TCC (p = 0.012) measured at the stable time point were found to be positively associated with FEV1% decline independently of GM-CSF. Backward selection of a multivariate model containing GM-CSF (APE), IL-5 (APE), IL-10 (APE), and TCC (Stable) produced the final model presented here.
dEstimates of the predicted total number of APE during 5 years of follow up per unit change in log scale biomarkers measured during clinical stability. Results show a quasi-Poisson regression model for the association with number of APE during 5 years of follow-up. HMGB-1 (log scale) was the only significant univariate (p<0.05), but CRP, IFN-α and IL-8 (all log scale) had trends toward significance (p<0.2). Backwards multivariate model selection retaining adjustment variables for follow-up time and low or high number of APE in the year prior to stable sputum collection (low  =  0 or 1 (reference group), high >1) as an indicator of baseline inflammation, retained only HMBG-1. A 1 unit change in log scale HMGB-1 is associated with a mean change in number of APE of 0.34.