In individuals with cystic fibrosis (CF), the integrity of the Cystic Fibrosis Foundation Patient Registry (CFFPR) is key to the efforts of those who seek to explore epidemiologic patterns of the disease, according to findings from a study published in the Annals of Epidemiology.
The CFFPR is responsible for obtaining data on the health and status of Americans who are diagnosed with CF, cystic fibrosis transmembrane conductance regulator (CFTR)-associated metabolic syndrome, and CFTR-related conditions who receive care at Cystic Fibrosis Foundation-accredited CF care centers and who have provided consent to participate between 1986 and the present day.
Only accredited CF care centers send their data to the CFFPR; those with CF who receive treatment outside of the network do not provide the CFFPR with any information. Among patients who are living with CF in the United States, participation in CFFPR has been estimated at between 81% and 84%.
It is well known that those lost to follow-up (LTFU) in the CFFPR are vitally important in exploring the epidemiology of the disease, with unreported deaths impacting survival estimates if LTFU is related to the course of CF. In the current analysis, the researchers described the LTFU population between 1986 and 2017 from the CFFPR, using the National Death Index to identify related deaths. In recent years, about 3% of patients who participate in the CFFPR in a single calendar year are LTFU in the following calendar year.
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“LTFU occurs when individuals no longer contribute data.” It is often observed in cohort studies that require patient participation over many years, with the structure of CFFPR mirroring that of an open cohort study. Of note, LTFU is a source of “selection bias” if patients LTFU differ systematically compared with those who remain in a cohort.
A total of 10,582 individuals LTFU were identified from 1987 through 2018 in the CFFPR. Among these persons, the following diagnoses were rendered:
- 9048 diagnosed with CF
- 591 diagnosed with CRMS
- 274 diagnosed with a CF-related disorder
- 669 not diagnosed with any of the 3 disorders
Further, among the 10,582 individuals LTFU in CFFPR, 23.2% (2460 of 10,582) of them matched a death recorded in the National Death Index. The following characteristics were noted among individuals who died after being LTFU:
- 43.0% females
- 90.9% of Caucasian race
- 58.9% diagnosed with advanced CF lung disease, per the last CFFPR recorded forced expiratory volume in 1 second percent predicted of less than 40%
- 18.1% were post-lung transplantation
When mortality and additional person-time among those LTFU were included in the analysis, the point estimate of median predicted survival for most of the time periods changed, increasing the point estimate from 2009 onward. When National Death Index data were included, the median predicted survival age in the time period between 2013 and 2017 rose from 44.3 years (95% CI, 43.2-45.7) to 45.8 years (95% CI, 44.5-47.1).
“Because the integrity of the CFFPR is critical to our efforts, improving registry retention should be a priority in order to capture, understand, and improve the clinical course of everyone with CF in the United States and accelerate our progress on the path to a cure,” the investigators concluded.
Ostrenga JS, Brown AW, Todd JV, et al. Impact of loss to follow-up on survival estimation for cystic fibrosis. Ann Epidemiol. Published online August 5, 2023. doi:10.1016/j.annepidem.2023.07.008