The purpose of this study is to evaluate the effectiveness and safety of the Dexcom G4 System when used as an adjuvant to blood glucose testing over a 7-day period in people 2 to 17 years-old with diabetes mellitus.

Performance of the system will be primarily evaluated by comparing the blood glucose measurements from the reference device, a blood glucose meter, to the CGM System values collected during the study. Specifically, performance will be primarily evaluated in terms of the proportion of G4 System values that are within ±20% of glucose meter reference value for glucose levels >80 mg/dL and ±20 mg/dL of glucose meter reference values <80 mg/dL. These G4-meter matched pairs will be analyzed across the 7 days of wear.

Safety data of the CGM System will also be collected and safety will be characterized by the incidence of anticipated device-related adverse events (ADEs) of subjects who participate in the study.

Inclusion Criteria:

• Ages 2 to 17 years;
• Diagnosis of diabetes mellitus;
• Treatment of diabetes with insulin and/or oral diabetes medication Note: Insulin-using subjects only - willing to avoid insulin injections or wear an insulin pump insertion set within 3 inches from the sensor site;
• Willing to refrain from the use of medications containing acetaminophen during the sensor insertion period and for one day prior to sensor insertion;
• Able to perform up to 7 fingersticks per day during home use (approximately 2 calibration fingersticks or as often as prompted by the device and approximately 5 for diabetes management and/or detection of hyper and hypoglycemia); and
• Subject or guardian is able to speak, read, and write English.

Exclusion Criteria:

• Extensive skin changes/diseases that preclude wearing the required number of devices on normal skin (e.g. extensive psoriasis, recent burns or severe sunburn, extensive eczema, extensive scarring, extensive tattoos, dermatitis herpetiformis) at the proposed wear sites;
• Known allergy to medical-grade adhesives;
• For subjects of childbearing potential: are pregnant as demonstrated by a positive pregnancy test within 72 hours prior to device insertion;
• Hematocrit value outside the range of the blood glucose monitoring system used in the study;
• Current participation in another investigational study protocol (if a subject has recently completed participation in another drug study, the subject must have completed that study at least 30 days prior to being enrolled in this study);
• Planned MRI scan, CT scan, or diathermy during the week of the study; or
• Any condition that, in the opinion of the Investigator, would interfere with their participation in the trial (e.g., marked visual impairment) or pose an excessive risk to study staff handling venous blood samples (e.g., known history of hepatitis B or C, or HIV).

Children and adolescents with diabetes mellitus (Type 1 or Type 2)