Delayed diagnosis of cystic fibrosis: clinical burden and missed opportunities in a cohort from Rio de Janeiro, Brazil.

Objective: To describe clinical and epidemiological profile of patients with cystic fibrosis (CF) diagnosed outside neonatal screening programs at two referral centers in Rio de Janeiro, Brazil, and to assess the impact of diagnostic delay on disease severity at the time of diagnosis. Methods: This cross-sectional study included 54 patients with a confirmed diagnosis of CF evaluated at two CF referral centers in Rio de Janeiro between 2019 and 2023. Data collected included age at diagnosis, neonatal screening history, clinical manifestations at diagnosis, previous misdiagnoses, microbiological findings, pulmonary function, and nutritional status. Patients were stratified by age at diagnosis (< 5, 5-12, 13-17, and ≥ 18 years) and by pediatric versus adult diagnosis. Chi-square tests were used for categorical comparisons. Results: Among the 54 patients, 59.3% were male, and 98.1% were not identified by neonatal screening. Median age at diagnosis was 11 years (IQR: 4.5-23.5). Diagnosis during adulthood occurred in 31.5% of patients. Bronchiectasis was present in 88.2% of adults compared with 47.1% of pediatric cases (p = 0.0045). CF-related diabetes was exclusively observed in adults (41.2%; p < 0.001). Prior misdiagnosis occurred in 45 patients (83.3%), most commonly asthma (24.1%), tuberculosis (11.1%), or idiopathic bronchiectasis (7.4%). At diagnosis, the median FEV Conclusions: Late CF diagnosis in Rio de Janeiro occurred predominantly outside neonatal screening programs, with a median age at diagnosis of 11 years, reflecting substantial missed opportunities for early intervention. Diagnosis during adulthood is associated with higher rates of bronchiectasis and CF-related diabetes, highlighting the irreversible structural and metabolic burden associated with diagnostic delay.