Screening for Cystic Fibrosis-Related Diabetes
The most appropriate counseling is to perform an oral glucose tolerance test (OGTT) yearly starting at age 10 years (Option A). This is the gold standard screening method recommended by all major diabetes and cystic fibrosis guidelines.
Why OGTT is the Correct Answer
Annual OGTT screening should begin by age 10 years in all patients with cystic fibrosis who do not have diabetes. 1, 2 This recommendation is consistent across the American Diabetes Association Standards of Care from 2015 through 2025 and represents the highest level of guideline evidence.
- The OGTT is explicitly recommended as the screening test of choice for cystic fibrosis-related diabetes (CFRD) by the American Diabetes Association. 2
- This annual screening continues throughout the patient's life, not just until age 18, making Option C incorrect. 1
Why Other Options Are Incorrect
Fasting Blood Glucose (Option B)
- Fasting blood glucose alone is not recommended for CFRD screening because it lacks sensitivity to detect the glucose abnormalities characteristic of cystic fibrosis. 1
- The pathophysiology of CFRD involves insulin insufficiency that manifests primarily with postprandial hyperglycemia, which fasting glucose would miss. 1
Random Blood Glucose (Option D)
- Random blood glucose every six months is inadequate for CFRD screening and is not supported by any guideline. 1
- While random glucose abnormalities may prompt earlier evaluation, they are not the recommended systematic screening approach. 3
Age Limitation (Option C)
- Screening does not stop at age 18; it continues annually throughout adulthood since CFRD prevalence increases with age (40-50% of adults develop CFRD). 1
Critical Clinical Context
Why CFRD Screening Matters
- CFRD is the most common comorbidity in cystic fibrosis, affecting approximately 20% of adolescents and 40-50% of adults. 1, 2
- Diabetes in CF patients is associated with worse nutritional status, more severe inflammatory lung disease, and greater mortality from respiratory failure. 1, 2
- Early diagnosis and treatment with insulin has been shown to preserve lung function and improve outcomes. 1, 2
Important Caveats
- Weight loss or failure of expected weight gain at any age should prompt immediate OGTT screening, regardless of whether the patient is under 10 years old. 1, 2
- A1C is explicitly NOT recommended as a screening test for CFRD due to low sensitivity in this population. 1, 2
- Continuous glucose monitoring may be more sensitive than OGTT for detecting early glucose abnormalities, but this approach requires more validation before replacing OGTT as the standard screening method. 1, 4, 5