This is a pilot outpatient study conducted at Stanford to obtain preliminary data on how Fiasp® works in a closed-loop system and to determine if any changes need to be made to the 670G pump to optimize the use of Fiasp®.

This will be a randomized cross-over blinded study and to see how the 670G pump responds to the introduction of Fiasp® insulin. Subjects enrolled in the study will have a 2 week period of optimization with weekly assessments of their Carelink download before entering the blinded phase of the study. They will use their usual home insulin during the optimization phase. They will then be started on their first blinded insulin (aspart or Fiasp®) which they will use for 2 weeks, before they cross-over to the other insulin.

Inclusion Criteria:

1. Clinical diagnosis of type 1 diabetes and using 670G pump for at least 1 month, and willing to have the 670G pump downloaded into a Carelink Clinical research database.
2. The diagnosis of type 1 diabetes is based on the investigator's judgment; C-peptide level and antibody determinations are not needed.
3. Age ≥18 years
4. Using Novolog or Fiasp® insulin at time of enrollment
5. Willing to use Fiasp® insulin
6. Total daily insulin dose is at least 0.3 units/kg/day
7. Usual carbohydrate intake is at least 60 grams a day, and willing to have at least 25 grams of carbohydrates for breakfast
8. For females, not currently known to be pregnant
9. An understanding of and willingness to follow the protocol and sign the informed consent
10. Willing to have photographs taken of their infusion sites
11. Willing to download their 670G pump every 1-2 weeks to a research Carelink account
12. Willingness to answer a brief online questionnaire every 2 weeks
13. Must be able to understand spoken or written English
14. For subjects participating in Part 2 of this study they will need to be using Fiasp® as part of their usual care
15. Hemoglobin A1c between 6 and 10% at the time of enrollment

Exclusion Criteria:

1. Pregnant or lactating females
2. No hypoglycemic seizure or loss of consciousness in the past 6 months
3. Severe episode of DKA in the 6 months prior to study enrollment that was unrelated to an infusion set failure
4. No known cardiovascular events in the last 6 months
5. No active proliferative diabetic retinopathy
6. Known tape allergies
7. Current treatment for a seizure disorder
8. Cystic fibrosis
9. Active infection
10. A known medical condition that in the judgment of the investigator might interfere with the completion of the protocol
11. Inpatient psychiatric treatment in the past 6 months
12. Presence of a known adrenal disorder
13. If on antihypertensive, thyroid, anti-depressant or lipid lowering medication, with lack of stability on the medication for the past 2 months prior to enrollment in the study
14. Abuse of alcohol
15. Dialysis or renal failure
16. Known eGFR <60%

Note: Adequately treated thyroid disease and celiac disease do not exclude subjects from enrollment.

Participants who completed the protocol are included in the analysis.

6 weeks

Double-blinded