Closed/Open Loop: determines whether Loop will enact its recommended temporary basal adjustments automatically (closed) or wait for your approval of each recommendation first (open) - note that the latter requires that you click on the recommended basal line before it will implement changes
Correction Range: sets the blood glucose range that you want Loop to target to and ideally maintain; can be a single number (e.g. 100-100 mg/dL) or a range (112-125 mg/dL), the latter generally functions more effectively
Overrides (Pre-Meal): *optional - sets the blood glucose range that you want Loop to target specifically before meals (typically lower than your usual correction range). This functions similar to a pre-meal bolus - the idea is for Loop to deliver a little more insulin in advance of the meal to bring your blood glucose levels lower and help preempt and minimize the spike from that meal. Note that this feature needs to be activated before each meal and will remain in effect until either it is turned off, one hour elapses, or carbs are entered.
Suspend Threshold: *required - set the lower limit above which Loop will always try to maintain your blood glucose. If any part of your predicted blood glucose curve in the next 30 minutes is calculated to go below the suspend threshold, Loop will wait until your predicted glucose is expected to climb above to recommend any boluses. Meanwhile, if either your current blood glucose or predicted blood glucose is below the suspend threshold, Loop will default to a temporary basal rate of 0 units/hr.
Basal Rates: Sets the amount of insulin you received per hour, delivered as small increments of rapid-acting insulin every 5 minutes. These rates can vary throughout the day but are intended to keep your blood glucose stable between meals and during sleep. Note that you must first add a pump in Loop settings before you can enter basal rates.
Maximum Basal Rate: sets the maximum temporary basal rate that you will allow Loop to use in order to bring and maintain your blood glucose into your correction range (typically set at around 3-4 times your highest scheduled basal rate). Note that as you start using Loop, it makes sense to play it safe and start with a lower maximum basal rate, to give Loop less room to be too aggressive. Over time, as you become more familiar and confident with how Loop manages your insulin delivery, you can gradually increase your maximum basal rate.
Maximum Bolus: sets the maximum amount that you will allow Loop to give for a single bolus. Note that this probably shouldn’t exceed the most you’ve given for a large meal, and could serve as a safety measure against accidentally inputting too large a bolus dose.
Insulin Model: selects the insulin activity model that Loop will use to estimate the effects of insulin on your blood glucose levels over time. We recommend that you choose the model that matches the insulin you use (Rapid-Acting Adults or Children if you are using Humalog or Novolog, Fiasp if you are using Fiasp) - these curves were derived from study patient data and are likely to best reflect how your body responds to your specific insulin.
Carb Ratios: tells Loop how many grams of carbs each unit of insulin is expected to cover for meals. These ratios can vary throughout the day and are used to calculate each of your meal boluses.
Insulin Sensitivities: tells Loop how much of a drop in blood glucose to expect from one unit of insulin. Traditional pumps only use this information to calculate how much insulin to give for corrections, but insulin sensitivity also has a far more consequential role in Loop - it is used in every Loop calculation (every 5 minutes) and plays an important part in Loop's prediction curve. It is therefore incredibly important to test and accurately confirm your sensitivity!
Override Presets: allows you to create new and edit existing override presets that inform Loop that you anticipate your insulin needs will change for a period of time (during situations such as exercise, illness, or hormone cycles), without having to modify all of your settings individually.
Tapping the “+” in the top right corner lets you create a new preset, where you can specify the:
- Symbol used to identify the preset
- Name for the preset
- Overall insulin needs relative to your current settings (will increase or decrease all of your basal, bolus, and correction insulin dose amounts by a specific percentage, adjustable in 10% increments). Consider setting a lower percentage than 100% when you expect yourself to be more insulin sensitive (e.g. during & after aerobic exercise), and a higher percentage than 100% when you expect yourself to be more insulin resistant (e.g. illness, menstrual cycles)
- Target range of blood glucose that Loop will aim for while the preset is active
Duration that the preset will remain active (you can have the preset enabled indefinitely until you turn it off, or set a desired amount of time in 15 minute increments)
Access by tapping the Glucose section on the main screen
Loop tries to account for four different factors in its glucose prediction model (the latter two are more complicated to understand but help Loop adapt its predictions to the situation), all of which we recommend you enable:
Insulin - the insulin model you’ve selected and the total amount of active insulin (including from boluses and temporary basal rates in the past 6 hours) at any given time is used to predict the anticipated drop in glucose over the next 6 hours
Carbohydrates - the quantity (in grams) of carbohydrates consumed and the carbohydrate absorption time inputted with each carb entry are used to predict how quickly and how much a meal is expected to raise glucose levels; real-world absorption rates can vary widely so Loop uses a “dynamic carb absorption model” that then adjust predictions based on observed changes in glucose (meaning Loop is forgiving and absorption times are not critical to get exactly right)
Glucose momentum - assumes that recent glucose trends are likely to persist for a short time (i.e. “the best predictor of the future is the recent past”), and projects some of the glucose trajectory in the past 15 minutes to continue over the next 30 minutes
Retrospective correction - allows the Loop algorithm to account for additional factors (e.g. exercise, stress, hormones, greater insulin resistance with higher glucose levels) by comparing predicted versus actual observed changes in blood glucose in the last 30 minutes, then applying those effects forward over the next hour. In essence, enabling retrospective correction lets Loop respond more aggressively to discrepancies between observed and predicted glucose) but is not absolutely better for everyone.