CD40LG and cystic fibrosis: When cases were stratified by severity of illness, milder disease was associated with improved sensitivity of serologic testing for ID (11/13 84.6% CI 57.8–97.3 for mild, 18/33 54.5% CI 38.0–70.2 for moderate, and 8/16 50% CI 28.0–72.0 for severe), CF (9/15 60% CI 35.8–80.2 for mild, 9/24 37.5% CI 21.2–57.3 for moderate, and 5/12 41.7% CI 19.3–68.1 for severe), and IgG/IgM EIA (18/19 84.2% CI 82.4–100.0 for mild, 51/63 81.0% CI 69.6–88.8 for moderate, and 13/21 61.9% CI 40.9–79.3 for severe).