A-F, Box-and-whisker plots showing sputum biomarkers and pulmonary exacerbations. A, Sputum sialic acid was elevated in patients who experienced PEX2+ in the year after study entry relative to those with PEX 0. B, Sputum hypoxanthine was elevated in those who experienced PEX 2+ as well as those who experienced PEX 1. C-F, Similar observations were made for xanthine (C), MTA (D), adenine (E), and GSH (F). ∗P < .05, ∗∗P < .01, or ∗∗∗P < .001 vs PEX 0, respectively. P values from Tukey multiple comparisons test after analysis of variance. GSH = glutathione; MTA = methylthioadenosine; PEX 0 = 0 pulmonary exacerbations; PEX 1 = one pulmonary exacerbation; PEX 2+ = two or more pulmonary exacerbations.