When should a child with Cystic Fibrosis (CF) be screened for Type 1 Diabetes Mellitus (T1DM)?

Screening for Diabetes in Children with Cystic Fibrosis

The correct answer is D. OGTT annually. Annual screening for cystic fibrosis-related diabetes (CFRD) with an oral glucose tolerance test (OGTT) should begin by age 10 years in all children with cystic fibrosis who have not previously been diagnosed with CFRD.

Rationale for OGTT as the Preferred Screening Method

• OGTT is specifically recommended as the screening test of choice for CFRD by the American Diabetes Association (ADA) in their most recent 2024 Standards of Care 1
• Annual OGTT screening should begin by age 10 years in all patients with cystic fibrosis not previously diagnosed with CFRD 1
• A1C is explicitly not recommended as a screening test for CFRD due to low sensitivity, making option A (HbA1c every 6 months) incorrect 1
• While a fasting blood glucose test (option B) is simpler, it lacks sensitivity for detecting the early glucose abnormalities that are common in CF patients 2
• Option C (no screening until ≥18 years) contradicts guidelines and would miss early CFRD cases, which is critical since CFRD affects approximately 20% of adolescents with CF 1

Importance of Early CFRD Detection

• CFRD is the most common comorbidity in people with cystic fibrosis, occurring in about 20% of adolescents and 40-50% of adults 1
• Diabetes in CF patients is associated with worse nutritional status, more severe inflammatory lung disease, and greater mortality from respiratory failure 1
• Early diagnosis and treatment of CFRD has been shown to improve clinical outcomes and preserve lung function 1, 3
• The Cystic Fibrosis Foundation Patient Registry has demonstrated that early diagnosis and treatment of CFRD was associated with preservation of lung function 1

Clinical Considerations for CFRD Screening

• Insulin insufficiency is the primary defect in CFRD, with genetically determined β-cell function and insulin resistance associated with infection and inflammation also contributing 1
• Regardless of age, weight loss or failure of expected weight gain is a risk for CFRD and should prompt immediate screening 1
• Annual monitoring for complications of diabetes is recommended beginning 5 years after the diagnosis of CFRD 1
• While annual OGTTs are perceived as burdensome (with only 30% of adults with CF having annual OGTTs), they remain the gold standard for diagnosis 1

Emerging Research and Alternative Approaches

• Recent publications suggest that an A1C cut point threshold of ≥6.5% is consistent with a diagnosis of CFRD and reduces patient screening burden, but A1C is still not recommended as the primary screening tool 1
• Alternative OGTT characteristics such as glucose curve shape, time to glucose peak, and one-hour glucose value ≥155 mg/dL during OGTT may help identify early glucose metabolism alterations in children with CF 4
• Continuous glucose monitoring (CGM) may be more sensitive than OGTT to detect risk for progression to CFRD; however, evidence linking these results to long-term outcomes is lacking 1

Common Pitfalls to Avoid

• Relying solely on A1C for screening can miss cases of CFRD due to its low sensitivity in this population 1
• Waiting for symptoms to appear before screening is dangerous as the initial presentation of CFRD may be clinically silent 2
• Delaying screening until adulthood (≥18 years) would miss early cases, as studies show that abnormal glucose tolerance in children with CF aged 6-9 years identifies those at high risk for progression to early-onset diabetes 5
• Assuming that screening before age 10 is not valuable - while guidelines recommend starting at age 10, children with weight loss or failure to gain weight should be screened regardless of age 1