Tidepool Chief Medical Advisor and pediatric endocrinologist Dr. Saleh Adi discusses guidelines to help you optimize insulin sensitivity factor (ISF) settings with your diabetes patients. Drawing from his decades of clinical practice, he highlights example case studies and ISF or correction factor optimization techniques, which you can also find in our webinars library.
The importance of ISF
Insulin sensitivity factor, also known as correction factor, refers to the number of milligrams per deciliter (mg/dL) or millimoles per litre (mmol/L) by which a person with diabetes’ blood glucose levels fall when they take a unit of insulin. A patient’s ISF is dynamic, with different sensitivity requirements throughout the day and regularly changing over a patient’s lifespan.
This volatility and need for personalization places additional pressure on healthcare providers’ limited time, but with Tidepool’s software and Dr. Adi’s guidelines, you can more quickly identify the root cause of problems, make these necessary adjustments more confidently, and reclaim more time to focus on goal-setting and conversations with your patients.
Even with patients using automated insulin dosing (or closed loop) systems, it’s important to review ISF settings regularly. While closed loop systems are designed to predict what the patient’s glucose is going to be in the near future and how to adjust their insulin, systems differ in how they do or do not use the manually-inputted ISF settings to make those calculations, in and out of closed loop modes. The more optimized the ISF settings, the more effective the system will be — otherwise it will have to “chase” the blood glucose.
Factors to keep in mind
The ISF changes dramatically throughout childhood and adolescence and may change from one unit of insulin for a 500 mg/dL change in an infant to more aggressive ratios like one unit for a 25 mg/dL reduction in an adult. Dr. Adi recommends having three to four different ISF settings per patient, reviewing ISF settings every 4–6 weeks in children and every few months in adults to stay on top of physiological changes.
“Data review and adjustment should be done frequently, like every four to six weeks in children. Although less than that in adults because [their insulin sensitivity factors] don’t change as much.”
It’s also important to remember that the ISF should follow the basal pattern because they both reflect the insulin sensitivity. You may want to review our recent blog post on “Optimizing basal rates,” as having a steady and functional basal rate in the background isolates the effect of the patient’s basal rate from the effect of the patient’s boluses for carbs and corrections. We also identified a common pattern that basal rates follow — where at certain times of the day a patient may be more insulin-resistant and require more insulin (e.g. first thing in the morning), and at other times the patient may be more insulin-sensitive and require less insulin (e.g. at dinnertime).
Similarly to basal rates, the insulin sensitivity factor may not be the same all day. When your patient is more sensitive to insulin, they may need a weaker ISF and when your patient is more resistant to insulin, they may need a stronger ISF.
As you can see from this graph, children generally require less basal insulin overnight, experience their largest glucose spike at around 6:00 am, and their second highest glucose spike after dinner. Adults follow a similar morning pattern, but may maintain a more consistent basal rate throughout the day.
Identify and evaluate ISF patterns
Finding “pure events” is key for assessing and calculating ISF. Dr. Adi says the following four factors contribute and make up what he considers to be a pure event:
- A single insulin dose for a meal or correction.
- Preceded by a stable CGM (continuous glucose monitor) trace for at least one hour.
- Followed by no events — including carbs, corrections, or moderate to high intensity exercise — for three to four hours.
- A stable basal rate in the background.
To identify patterns and evaluate ISF settings, Dr. Adi recommends using the Daily View in Tidepool Web to see actionable information based on your patient’s insulin pump, blood glucose meter, and CGM data all in one place.
As you’re reviewing patient data to identify and evaluate ISF patterns, identify at least three to four similar events over a maximum period of three weeks to make sure you’ve identified a pattern that requires optimization.
At the end of the day, Dr. Adi believes that knowing and trusting your patients is going to go a long way towards helping you get their ISF settings right. When you and your patient work together, you can feel more confident that their day-to-day diabetes management has been made a little easier and that you’re getting all the relevant information you need to adjust their settings, empowering both you and your patients to focus more on what matters
Have any follow-up questions about ISF optimization? Check out our full “Helping your patients optimize ISF” webinar via our webinars library, or explore our other Tidepool for telemedicine videos on our YouTube page.