Screening for Diabetes in Children with Cystic Fibrosis
The correct answer is D: Annual OGTT screening should begin by age 10 years in all children with cystic fibrosis, as this is the only method recommended by current guidelines for detecting cystic fibrosis-related diabetes (CFRD). 1, 2
Why OGTT is the Gold Standard
The American Diabetes Association explicitly states that OGTT is the screening test of choice for CFRD and that A1C is NOT recommended as a screening test due to low sensitivity. 1, 2 This eliminates option A (HbA1c every 6 months) as an appropriate screening method.
- OGTT is superior to other screening methods because it detects the insulin insufficiency that is the primary defect in CFRD 1
- Fasting blood glucose alone (option B) is inadequate because it misses postprandial hyperglycemia, which often occurs earlier in the disease course 3
- The recommendation for annual screening starting at age 10 is based on evidence from the Cystic Fibrosis Foundation Patient Registry, which showed that early diagnosis and treatment of CFRD preserves lung function 1
Why Age 10 Years is the Threshold
Annual OGTT screening should begin by age 10 years in all patients with CF not previously diagnosed with CFRD. 1, 2 This eliminates option C (no screening until ≥18 years), which would miss the approximately 20% of adolescents who develop CFRD 1, 2.
- The prevalence of CFRD increases markedly with age: 5% in children aged 5-10 years, 11% in those aged 10-18 years, and 27% in adults over 18 years 4
- CFRD is associated with worse nutritional status, more severe inflammatory lung disease, and greater mortality compared to CF patients without diabetes 1, 2
Critical Exception to the Age 10 Rule
Regardless of age, weight loss or failure of expected weight gain should prompt immediate OGTT screening, even in children younger than 10 years. 1, 2 This is a common pitfall to avoid—don't wait until age 10 if there are clinical red flags.
- Research shows that 42% of children with abnormal glucose tolerance detected between ages 6-9 years progressed to diabetes by age 11-12 years, much earlier than the typical age of 23 years in the general CF population 5
- Every third child with CF aged 5-10 years already has some form of abnormal glucose tolerance 4
Why Other Screening Methods Are Inadequate
- HbA1c has low sensitivity for CFRD and will miss cases, making it inappropriate for screening despite being easier to perform 1, 2
- Fasting blood glucose alone misses the postprandial hyperglycemia that characterizes early CFRD 3, 6
- Continuous glucose monitoring may be more sensitive than OGTT for detecting risk of progression, but evidence linking these results to long-term outcomes is lacking, so it cannot replace OGTT for screening 2
Clinical Implications
- CFRD occurs in approximately 20% of adolescents and 40-50% of adults with CF 1, 2
- The disease is associated with insulin insufficiency as the primary defect, with additional contributions from genetically determined β-cell dysfunction and insulin resistance from infection and inflammation 1
- Beginning 5 years after CFRD diagnosis, annual monitoring for diabetes complications is recommended 1, 2