Immunoglobulin G: A useful outcome marker in the follow‐up of cystic fibrosis patients?

BACKGROUND AND METHODS: Hypergammaglobulinemia (hyper‐IgG) and hypogammaglobulinemia (hypo‐IgG) have been reported in patients with cystic fibrosis (CF). Although the clinical respiratory course is paradoxically different, depending on the IgG status, this association remains elusive. Therefore, we performed a longitudinal study to assess the annual evolution of IgG profiles in a cohort of pediatric patients with CF, from their diagnosis until 2016. We then compared clinical findings with the patients’ IgG status to determine whether IgG status could reflect the respiratory clinical course of patients with CF. RESULTS: Among the 66 patients with CF that were aged between 12 months and 18 years in 2016 (mean age: 9.3 years [SD: 5.2]), hypo‐IgG was observed in 15.2% and no hyper‐IgG was identified. Longitudinal assessment since diagnosis revealed no hyper‐IgG but 33.3% of patients had at least one sample showing hypo‐IgG, among which two patients displayed persistent hypo‐IgG. The number of pulmonary exacerbations, duration of antibiotic therapy, and erythrocyte sedimentation rate were all lower in hypo‐IgG patients. No difference was observed for the genotype, chronic Pseudomonas aeruginosa or Staphylococcus aureus infection, and in the parameters of lung function. CONCLUSION: The IgG profile of pediatric patients with CF has changed over recent decades, particularly with regard to hyper‐IgG. In a significant portion of the pediatric CF population, hypo‐IgG is transient and only identifiable in longitudinal assessments. This study reinforces that hypo‐IgG patients paradoxically present a more favorable course of clinical status. Therefore, IgG levels could be a useful outcome marker in the follow‐up of patients with CF.