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Step 10: Test Settings

Time Estimate

  • 2 hours to read the rest of LoopDocs (particularly the "Set up App", "Operate", and "FAQ" sections) and LoopTips thoroughly and thoughtfully
  • 15 minutes to take this quiz to make sure you've familiarized yourself with Loop's expected behavior
  • 1-3 days to test settings for safety and to get the most out of Loop


  • A small amount of effort to test/validate basal rates, ISF (correction factor), and carb ratios will eliminate a lot of uncertainty when you start Looping
  • Keep an open mind that settings may need to change as you start Loop
  • Hormones, illness, and failed sites can still happen


  • "My endo makes my pump settings, so do I really need to test them?" Well, nobody is going to force you, but testing your settings even just a couple days will give you a tremendous advantage going into Loop. Your endo may have adjusted your settings in a very different context, with different constraints. What is safe and ideal in traditional pump therapy, may not be the best selection for the Loop app. So, keep an open mind and be willing to adjust settings with the Loop app.
  • "I have great control, why would I need to test my settings?" Awesome for you! However, it is quite possible that your "great control" comes with a lot of little adjustments all the time. We all got used to needing little bumps and nudges of insulin or carbs over time...and sometimes those bumps and nudges are covering for underlying settings that need adjustment. Testing your settings will help...especially if you are coming from a treatment style that involves memorizing your insulin doses for may not know your actual carb ratio or ISF as a result of "just knowing" your boluses.
  • "I can't basal test with my 2-year-old. What can I do?" That is pretty tough. Consult your endo, watch your patterns, and do the best you can...little kiddos are a difficult group to test settings.

Loop is just a fancy calculator underneath the hood. The math problems that it is solving depend on the settings that you provide. It's a good idea to make sure you do a bit of settings testing before using Loop.

Basal Rates

If the rates are properly set, Basal insulin will keep your blood glucose steady without food present. You can test your basal by having a relaxing 4-6 hours without eating at least two hours before you begin the test. Does your blood sugar stay steady? Or do you climb and need a correction? Or do you go low and need to eat? Setting basal is a crucial step to setting yourself up for Loop success. It determines how much of the insulin delivered (from basal and bolus) is counted as insulin on board (IOB).

Insulin Sensitivity Factor

The Insulin Sensitivity Factor (ISF), sometimes called Correction Factor, is how much one unit of insulin will bring down your blood glucose (BG). The higher the value of this setting, the more sensitive to insulin you are. An ISF of 30 means one unit of insulin lowers your BG 30 mg/dL in the absence of food or activity, if your basal rates are correct. You can test this setting, after you determine your basal rates. Simply bring yourself to a higher BG with a glucose tab or other small quick carbs. Wait until you see yourself plateau again at the higher BG, then make a correction. Wait 4-6 hours (again no food) and see where your correction lands your blood sugar. Divide the BG drop by the amount of correction insulin you delivered and that’s your ISF. Note, you can have more than one ISF in a 24 hour period. (Most of Loop configurations enable time-of-day settings - tap the + sign to add another row.)

Carb Ratio

The Carb Ratio (CR) is the amount of carbs covered by one unit of insulin. Ideally, a good carb ratio will restore your BG close to its starting point within 3 hours of the meal. (High fat/protein meals may cause BGs to be impacted longer.) If you are spiking higher than you’d like after a meal, but still coming back to the starting BG, consider prebolusing your meal by 15-20 minutes rather than changing the carb ratio.

Other Resources

Check for a discussion on how to check all these settings and why they are important. If you’re fascinated by this topic, read the book 'Think Like A Pancreas' for a really great discussion. Finally, remember settings can change periodically. Hormone cycles, steroids, illness, etc. may lead to a need to change settings.

Next Step: Make Plans for Loop Data

Now you are ready to move onto Step 11 to Make Plans for Loop Data.

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