Canadian patients with cystic fibrosis (CF) have better respiratory function and higher body mass index (BMI) than French patients, although they have higher blood glucose levels and a greater incidence of CF-related diabetes (CFRD), according to a long-term study.
The research was published in an article, “Glucose tolerance in Canadian and French cystic fibrosis adult patients,” in the journal Nature Scientific Reports.
About half of adult CF patients experience CFRD. Annual screening is recommended starting from age 10 due to the lower reliability of standard screening tests in this patient population, and the slow and often undetected first symptoms of CFRD.
Current data indicating differences in CFRD prevalence between European and North American children have come from annual registry reports exclusively, which frequently do not collect information about other glucose metabolism abnormalities. Also, the impact of different profiles of glucose tolerance, or how well the body processes glucose, on respiratory function has not been assessed in large groups of patients over long periods.
Therefore, a team in Montreal, Canada, and Lyon, France, used the Montreal Cystic Fibrosis Cohort and the Lyon Cystic Fibrosis Cohort to compare the clinical characteristics of 224 Canadian to 147 French adults with CF, as well as their glucose and insulin values, CFRD incidence, and the changes in pulmonary function over four years.
All patients had untreated CFRD, and underwent annual two-hour oral glucose tolerance tests, where fasting blood glucose and two-hour blood glucose were measured. Patients were divided into three groups based on their glucose tolerance status: normal glucose tolerant, abnormal glucose tolerant, or de novo CFRD.
Results showed that the Canadian patients (median age of 22.0 years, 58% men) had better median percent forced expiratory volume in one second (%FEV1, a measure of pulmonary function, which was 71.0% for Canadian patients vs 64.0% for French patients), and higher median BMI (21.1 vs. 19.9 kg/m2).
The Canadian group also had a higher proportion of patients (51.3%) with mild to normal predicted FEV1 (over 70%), compared with French patients (38.1%).
French patients more commonly had Staphylococcus aureus — 70.1% vs. 55.8% in the Canadian group. No differences were found in Pseudomonas aeruginosa, the number of intravenous antibiotics courses in the year preceding the study, or the proportion of people with CFRD mutations in both gene copies (homozygous).
In the Canadian group, blood glucose levels were higher at fasting (5.4 vs. 4.8 mmol/L for French patients) and at two hours (7.6 vs. 6.5 mmol/L for French patients). The Canadians also had higher fasting plasma insulin (3.8 vs. 3.2 for the French patients) and at two hours (27.4 vs. 18.1 for the French group).
The incidence of de novo CFRD diagnosis was higher in Canadian patients (19.2% vs. 9.8% for the other group), who also showed a lower proportion of patients with normal glucose tolerance (36.6% vs. 53.4%). Also, Canadian patients with normal glucose tolerance had higher %FEV1 (72.0) than French patients in the same group (64.0).
The higher median fasting blood glucose levels in Canadian patients were found across the three glucose tolerance groups. French patients with normal glucose tolerance had higher insulin sensitivity. In contrast, those with normal or abnormal glucose tolerance had lower insulin resistance than the Canadian patients.
The findings also showed that Canadian and French patients with normal or abnormal glucose tolerance showed similar variations in plasma insulin levels over the two hours of the oral glucose tolerance test. In those with CFRD and similar insulin values at the end of the test, Canadian patients exhibited slightly higher values at one hour than French patients.
Higher BMI correlated with better lung function across all glucose tolerance groups, but not with glycemia. Also, four-year variations in FEV1 did not differ in Canadian and French patients in the normal and abnormal glucose tolerance groups. However, Canadian patients showed a slower mean decline in FEV1 across the three groups.
“In conclusion, Canadian patients present a better clinical status (higher BMI, insulin secretion, and FEV1) than French patients, but unexpectedly they also present a higher incidence of glucose abnormalities,” the scientists wrote. Also, “the decline in FEV1 in patients with abnormal glucose tolerance is similar to that of patients with normal glucose tolerance.”
According to the team, “to better understand the complex interplay between glucose tolerance and clinical status (BMI and/or FEV1) of adult patients with CF, further investigations should focus on potential underlying factors that may play a role in the observed differences.”