Antibody detection by EIA (both IgM and/or IgG) had higher sensitivity (89/111, 80.2% CI 72.8–87.6) when using cutoff of EU/mL >10 or EU/mL >20 when compared to ID (39/66, 59.1% CI 47.2–71.0 P  = .0005 and P = .0013, respectively) and CF (23/52, 44.2% CI 30.7–57.7 P = .0006 and P = .0016, respectively). The gene discussed is CD40LG; the disease is cystic fibrosis.