Screening for Cystic Fibrosis-Related Diabetes
The correct answer is D: OGTT annually, beginning at age 10 years in all patients with cystic fibrosis not previously diagnosed with cystic fibrosis-related diabetes. 1
Primary Recommendation
Annual oral glucose tolerance test (OGTT) screening should begin by age 10 years in all patients with cystic fibrosis who have not been previously diagnosed with CFRD. 1 This is a consistent, high-level recommendation (Grade B evidence) across all American Diabetes Association Standards of Care from 2021 through 2024. 1
Why OGTT is the Gold Standard
OGTT is the recommended screening test of choice for cystic fibrosis-related diabetes because it has superior sensitivity compared to other methods. 1, 2
A1C is explicitly NOT recommended as a screening test for CFRD due to low sensitivity and should not be used for screening purposes. 1, 2 However, an A1C value ≥6.5% (≥48 mmol/mol) is consistent with a diagnosis of CFRD if already obtained. 1
Fasting blood glucose alone is insufficient for screening, as CFRD often presents with postprandial hyperglycemia before fasting hyperglycemia develops. 3, 4
Clinical Significance of CFRD
CFRD is the most common comorbidity in people with cystic fibrosis, occurring in approximately 20% of adolescents and 40-50% of adults. 1, 2, 5
Diabetes in CF patients is associated with worse nutritional status, more severe inflammatory lung disease, and greater mortality compared to CF patients without diabetes. 1, 2, 5
Early diagnosis and treatment of CFRD is associated with preservation of lung function and improved clinical outcomes. 1, 2
Important Exceptions and Red Flags
Regardless of age, weight loss or failure of expected weight gain is a risk factor for CFRD and should prompt immediate screening even before age 10 years. 1, 2, 5 This is a critical clinical pearl that overrides the routine age-based screening protocol.
Why Other Options Are Incorrect
Option A (HbA1c every 6 months): A1C is not recommended for screening CFRD due to low sensitivity. 1, 2
Option B (Fasting blood glucose annually): Fasting glucose alone misses many cases of CFRD, as postprandial hyperglycemia often precedes fasting hyperglycemia. 3, 4
Option C (No screening until age ≥18): This is incorrect as screening should begin at age 10 years, and delaying screening until adulthood would miss critical opportunities for early intervention. 1, 2
Additional Management Considerations
Once CFRD is diagnosed, insulin therapy is the treatment of choice to attain individualized glycemic goals. 1
Annual monitoring for diabetes complications should begin 5 years after CFRD diagnosis. 1
Insulin insufficiency is the primary defect in CFRD, with genetically determined β-cell function and insulin resistance from infection and inflammation also contributing. 1, 5
Common Pitfalls to Avoid
Do not rely on A1C for screening as it will miss the majority of CFRD cases due to low sensitivity in this population. 1, 2
Do not wait until age 18 to begin screening as significant morbidity can occur during adolescence if CFRD goes undetected. 1
Do not ignore weight loss or failure to gain weight at any age, as this should trigger immediate OGTT screening regardless of the patient's age. 1, 2, 5