Canadian Study: CGM Beats A1c for Cystic Fibrosis Diabetes

Canadian Researchers Find CGM May Replace Invasive Diabetes Screening in Cystic Fibrosis

A study from Canada, conducted at the Montreal Clinical Research Institute (IRCM) in Québec and published in the Journal of Cystic Fibrosis (2026), suggests that continuous glucose monitoring (CGM) could replace a burdensome standard screening test for diabetes in people living with cystic fibrosis (CF).

Why Cystic Fibrosis and Diabetes Are Linked

Cystic fibrosis-related diabetes (CFRD) is one of the most common complications of CF, affecting a significant portion of adults with the condition. Current guidelines — including those followed in the US — recommend yearly screening for CFRD starting at age 10. That screening relies on the Oral Glucose Tolerance Test (OGTT), a multi-hour procedure requiring patients to fast, drink a sugary solution, and have multiple blood draws. For people already managing a complex lung disease, this is a real burden.

The standard A1c blood test (which reflects average blood sugar over roughly three months) has historically been considered a poor screening tool for CFRD, and this Canadian study reinforces why: the unique way CF affects the pancreas means A1c often misses early or moderate cases.

What the French-Canadian Study Found

Researchers enrolled 107 adults with CF across a joint French and Canadian cohort. Each participant underwent an OGTT, wore a CGM device simultaneously, and had their A1c measured. Participants were grouped by glucose status: normal (73 people), impaired glucose tolerance (24 people), and confirmed CFRD (10 people). Notably, 63% of participants were taking Elexacaftor/Tezacaftor/Ivacaftor (brand name Trikafta), a newer CF modulator therapy.

Key CGM thresholds were measured in US-equivalent terms:

• Time above 140 mg/dL (7.8 mmol/L converted): The percentage of time spent over this level was a strong CFRD predictor — an AUC of 0.87 on diagnostic accuracy testing, compared to just 0.61 for A1c.
• Time above 180 mg/dL (10 mmol/L converted): Even stronger, with an AUC of 0.88.
• Critical finding: Spending more than 10% of monitored time above 140 mg/dL detected CFRD with 100% sensitivity — meaning it missed zero confirmed CFRD cases — though specificity was 46%, meaning some false positives occurred.

How This Compares to US Guidelines

US guidelines from the Cystic Fibrosis Foundation (CFF) currently recommend the OGTT as the gold standard for CFRD screening and do not endorse CGM as a primary screening replacement. This Canadian study does not contradict that position — the authors carefully note these are preliminary baseline findings and that prospective confirmation is needed. However, the data add meaningful weight to an emerging international push to validate CGM as a first-line screening step, potentially reserving the OGTT for borderline cases.

Why This Matters for US Patients

For Americans living with cystic fibrosis, this research offers real hope. If follow-up studies confirm these findings, CGM could eventually serve as a simpler, less invasive first screening step — catching CFRD early without requiring the full OGTT every year. Early CFRD detection is critical because unmanaged high blood sugar in CF accelerates lung function decline. Wearing a CGM for a monitoring period may one day replace a half-day clinic visit for annual screening.

If you or a loved one with CF is already using a CGM for diabetes monitoring or screening discussions, tools and resources available at mdsdiabetes.com can help you understand your CGM data and have more informed conversations with your care team about what your numbers mean.

Citation

Alexandre-Heymann, Reynaud, Grou (2026). Continuous glucose monitoring is a better indicator of glucose tolerance than HbA1c in cystic fibrosis. Journal of Cystic Fibrosis: Official Journal of the European Cystic Fibrosis Society. [Canada] PMID: 41253584. DOI: 10.1016/j.jcf.2025.11.003