Current guidelines on the diagnoses and management of cystic fibrosis (CF) related diabetes recommend treatment for diabetes based on diagnostic criteria derived from adults with type 2 diabetes. Increasing evidence supports treating early glucose abnormalities in cystic fibrosis patients to target CF specific outcomes, including lung function and nutrition (BMI-Body Mass Index). However, the criteria and timing of when to start insulin therapy in the 'prediabetic' state are unclear. A more accurate characterization of blood sugar variability in youth with and without CF will help the investigators better interpret continuous glucose monitor (CGM) findings in patients with CF prediabetes and diabetes and more accurately identify those individuals at greatest risk for disease progression.

Inclusion Criteria:

Healthy controls (n=45) -

1. Age 10-25 years
2. BMI <85th percentile
3. Baseline health at enrollment

CF controls (n=45) -

1. Age 10-25 years
2. Diagnosis of cystic fibrosis (by newborn screen, sweat chloride testing, or genetic testing)
3. Baseline health at enrollment (no inclusion/exclusion criteria for CF patients based on lung function, BMI, pancreatic insufficiency, or genotype)

CF prediabetes & CFRD (n=70)

1. Age 10-25 years
2. Diagnosis of cystic fibrosis (by newborn screen, sweat chloride testing, or genetic testing)
3. History of abnormal oral glucose tolerance testing (2h-glucose >140, fasting plasma glucose >100,1hr glucose >200)
4. If taking medication that affects glucose metabolism (ex. Insulin, insulin sensitizers, glucocorticoids, atypical antipsychotics), should be on a stable dose over the past 3 months

Exclusion Criteria:

Healthy controls -

1. Known diagnosis of diabetes or prediabetes (including type 1, type 2, MODY), abnormal oral glucose tolerance test (OGTT) (ie. fasting plasma glucose ≥100 or 2hr ≥140 mg/dl) or HbA1c ≥ 5.7%
2. BMI ≥85th percentile
3. Chronic disease that may affect glucose metabolism or use of medications affecting glucose metabolism in the past 3 months (ex. Insulin, insulin sensitizers, glucocorticoids, atypical antipsychotics)
4. Presence of type 1 diabetes auto-antibodies in any individuals with a first degree relative with type 1 diabetes (will only include first degree relatives if they have had previous negative auto-antibody screening performed as part of participation in other studies such as the Trial Net studies at the Barbara Davis Center)
5. Acute illness (ex. Asthma exacerbation, gastroenteritis, febrile illness)
6. Pregnancy

CF participants -

1. Diagnosis of type 1 diabetes, type 2 diabetes, or MODY
2. Varying doses of medication affecting glucose metabolism in the past 3 months
3. Pulmonary exacerbation associated with hospitalization, or systemic steroid requirement in the preceding 6 weeks
4. Pregnancy

Children and Adolescents ages 6-25, without diabetes. Out of 160 people, 45 will be healthy controls, 45 with Cystic Fibrosis (normal glucose tolerance), and 70 with Cystic Fibrosis-related diabetes or pre-diabetes.