Continuous Glucose Monitoring Parameter and Oral Glucose Tolerance Testing (OGTT) Parameters in Children and Young Adults With Cystic Fibrosis (CF)

As modulator therapy changes the landscape of cystic fibrosis (CF), children with CF will live longer and healthier lives with less pulmonary exacerbations. Still, other complications like Cystic Fibrosis Related Diabetes and underlying dysglycemia may become more apparent as lifespans of CF patients increase. It is therefore essential that clinicians have the tools to understand early stages of dysglycemia to prevent long term complications of CFRD. At present, 2 hours 75-gram OGTT remains the gold standard annual screen for CFRD. This test is both cumbersome for patients and limits a clinician's interpretation of glycemic control to a limited time frame. Although OGTT is currently used to diagnose CFRD, it can be cumbersome for patients and time consuming. OGTT compliance is therefore not surprisingly low in the CF population with about 49 % of CF centers having a more than 50% completion of annual OGTT. Continuous glucose monitoring (CGM), on the other hand, offers the ability to obtain more data on longer time periods in a much easier fashion. Thus, CGMs have the potential to glean a more fine-tuned understanding of a patient's glycemic control. Moreover, CGMs can make glycemic testing easier on patients, thereby increasing compliance of annual glycemic testing. The investigators hypothesize the correlation of CGM parameters of hyperglycemia like % of time > 180 mg/dl, % of time> 150 mg/dL with 1- and 2-hour OGTT glucose levels, Glucose Management Indicator (GMI), average glucose, glucose variability, and HbA1c levels. The investigators also aim to explore patient views and preferences of OGTT and CGM for screening of CFRD through surveys after CGM wear.

The investigators hope to be able to correlate 1- and 2-hour glucose values on OGTT to % in range parameters on a continuous glucose monitor. This will pave the way to better understand glycemic control in children with CF and risk for CFRD with data from a CGM even without an OGTT in the future. The investigators also hope to understand patient and parent/guardian preferences towards CFRD screening modalities.

Study Design: Prospective observational study. Eligible patients will have a CGM placed for up to10-day wear within the 3 months before or after clinically appropriate OGTT and A1c. OGTT testing will include 1- and 2-hour glucose levels and HbA1c as per standard of care. A Dexcom CGM will be placed in clinic onto the subjects upper arm. Survey exploring patient and parent/guardian preference will be provided after the CGM is removed.