Alternate Measures of Glucose During OGTT Testing for CFRD

Study Overview
=================
Brief Summary
-----------------
Although early detection and treatment of cystic fibrosis-related diabetes (CFRD) can lead to significant clinical improvements and prolong life, rates of screening are poor likely due to the burdensome nature of oral glucose tolerance testing (OGTT). The investigators propose to assess the feasibility and accuracy of two screening tools, continuous glucose monitoring (CGM) and a home OGTT kit (GTT@home). If this pilot study reveals acceptable accuracy of either device, this study will allow for future studies exploring home-based OGTT screening.

Detailed Description
-----------------
The investigators hypothesize that there will be strong agreement between plasma glucose and glucose as measured by either CGM or GTT@home at three different timepoints during an OGTT: fasting, 1-hour, and 2-hours.

Official Title
-----------------
Correlations Between CGM and Serum Glucose During OGTT Testing for CFRD

Conditions
-----------------
Cystic Fibrosis, Cystic Fibrosis-related Diabetes

Intervention / Treatment
-----------------
* Diagnostic Test: Oral glucose tolerance test


Participation Criteria
=================
Eligibility Criteria
-----------------
Inclusion Criteria: Diagnosis of cystic fibrosis ≥ 10 years of age Access to a smart phone compatible with the Dexcom G7 app, which is the only way to visualize real-time Dexcom G7 data Fluency in written and spoken English as the GTT@Home is currently only available in English Exclusion Criteria: Hospitalization or treatment with IV antibiotics or supraphysiologic glucocorticoids within 4 weeks Use of medications known to impact the accuracy of the Dexcom G7 (hydroxyurea, >2g acetaminophen per day) History of severe adhesive reactions that may lead to an inability to tolerate CGM wear

Ages Eligible for Study
-----------------
Minimum Age: 10 Years

Sexes Eligible for Study
-----------------
All

Accepts Healthy Volunteers
-----------------
No

Study Plan
=================
How is the study designed?
-----------------

Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| OGTT Cohort<br>All enrolled participants will complete an OGTT. | Diagnostic Test: Oral glucose tolerance test<br>* An oral glucose tolerance test will be completed. A fasting glucose will be measured. Participants will drink 1.75 g/kg of dextrose (up to a maximum of 75 grams) within 10 minutes. Glucose values will be measured at 1 hour and 2 hours.<br>|

What is the study measuring?
-----------------
Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Agreement between plasma glucose, CGM measured glucose using the Dexcom G7, and GTT@home glucose | Differences in fasting glucose will be measured by the difference in mg/dl between plasma glucose, CGM measured glucose, and GTT@home measured glucose. | Fasting glucose before OGTT | 
| Agreement between plasma glucose, CGM measured glucose using the Dexcom G7, and GTT@home glucose | Differences in the 1 hour glucose during the OGTT will be measured by the difference in mg/dl between plasma glucose, CGM measured glucose, and GTT@home measured glucose. | 1 hour mark in OGTT | 
| Agreement between plasma glucose, CGM measured glucose using the Dexcom G7, and GTT@home glucose | Differences in the 2 hour glucose during the OGTT will be measured by the difference in mg/dl between plasma glucose, CGM measured glucose, and GTT@home measured glucose. | 2 hour mark in OGTT | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Agreement between the categorical diagnosis of normal glucose tolerance (NGT), impaired glucose tolerance (IGT), indeterminate glycemia (INDET), and CFRD as defined by plasma glucose, CGM glucose, and GTT@home glucose. | Categorical diagnosis of glucose tolerance as measured by plasma glucose, CGM measured glucose using the Dexcom G7, and GTT@home glucose. | Up to 2 hours | 
| Difference between plasma glucose and CGM measured glucose after the fasting glucose | Absolute differences between the glucose measurements will be measured in mg/dL | Up to 20 minutes after the fasting glucose | 
| Difference between plasma glucose and CGM measured glucose after the 1 hour mark during the OGTT. | Absolute differences between the glucose measurements will be measured in mg/dL | Up to 20 minutes after the 1 hour mark in the OGTT | 
| Difference between plasma glucose and CGM measured glucose after the 2 hour mark during the OGTT. | Absolute differences between the glucose measurements will be measured in mg/dL | Up to 20 minutes after the 2 hour mark in the OGTT | 
| The ability of untrained participants to successfully complete the GTT@home kit without any guidance from the research team | Number of steps successfully completed as measured by the GTT@home instruction manual. | Up to 2 hours | 
| Impact of wearing a real-time CGM on participants' awareness of the importance of screening for and diagnosing CFRD. | 60 minute semi-structured interviews will be conducted with participants. Transcripts will be analyzed using semantic content analysis | Within 2 weeks after removal of the CGM | 
| Perceived benefits and burdens of CGM use | Participants will complete a CGM Benefits and Burdens survey, a 16-item measure used to assess perceptions of CGM technology in people with type 1 diabetes. Surveys may be completed on paper or online, as per the participant's preference. The survey is scored on a 5-point scale (agree/disagree scale). | Within 2 weeks after removal of the CGM | 

 Terms related to the study
=================
Keywords Provided by Centre Hospitalier Valida
-----------------
continuous glucose monitor, oral glucose tolerance test