Diagnostic yield of cystic fibrosis from a South Australian monocentric cohort: a retrospective study.

Objectives: To determine the diagnostic yield of cystic fibrosis (CF) using a two-tiered genetic testing approach. Although newborn screening includes CF, this typically only covers a selection of common genetic variants, and with over 2000 reported in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, we hypothesised that patients will be missed and present clinically later in life.

Design: A retrospective study over a 5-year period (January 2018-December 2022).

Setting: A single pathology service in South Australia.

Participants: A total of 1909 CF test referrals from patients with clinical suspicion indicated by respiratory and gastrointestinal manifestations, foetal echogenic bowel and male infertility and asymptomatic CF requests for reproductive carrier screening.

Primary And Secondary Outcome Measures: The number and type of CFTR gene variants detected in symptomatic and asymptomatic testing referrals.

Results: A total of 25 patients were diagnosed with CF or CF-related disorders (2.5%) with gastrointestinal symptoms yielding the highest diagnostic rate of 4.4%. Additionally, a total of 79 carriers (4.1%) were identified uncovering a carrier frequency of 1 in 24, which is consistent with the 1 in 25 reported in the Caucasian population. CF was found to be causative of foetal echogenic bowel in 0.83% of cases.

Conclusions: This study highlights the importance of considering CF in symptomatic patients, even in a nation with >99% of newborns screened for CF. Additionally, the identification of CF in this population supports the recommendation for CF genetic testing in reproductive healthcare.