From the Guidelines
The method to determine a patient's Insulin Sensitivity Factor (ISF) involves calculating how much the blood glucose will decrease on infusion of 1 unit of insulin, which is an individualized measure of the patient's sensitivity to insulin 1.
Key Factors
- The ISF is calculated based on the total daily dose of insulin and is a reflection of the patient's sensitivity to insulin 1.
- It is used with the bolus dose to correct a blood sugar above a prespecified target, before the next meal is taken 1.
- The ISF is expressed as a ratio, for example, 1:3, which means 1 unit of insulin would be expected to decrease the blood sugar by 3 mmol litre−1 1.
Calculation
- The ISF is calculated at the start of insulin pump therapy and is subject to change according to physiological changes such as weight, exercise, menstruation 1.
- The calculation involves measuring the patient's blood glucose levels before and after administering a dose of insulin, and then using the resulting glucose decline to calculate the ISF 1.
Clinical Application
- The ISF is individualized and preprogrammed into the insulin pump, allowing for accurate calculation of the bolus dose required to correct hyperglycemia 1.
- The ISF can vary throughout the day and can be set at different levels for different time blocks, taking into account factors such as the dawn phenomenon and regular daily activities 1.
From the Research
Determining Insulin Sensitivity Factor (ISF)
To determine a patient's Insulin Sensitivity Factor (ISF), several methods can be employed, as indicated by various studies 2, 3, 4.
- The 1800 rule can be used to estimate ISF, which is calculated as 1800 divided by the total daily insulin dose (TDD) 2.
- However, research suggests that the 1800 rule may not be accurate for all times of the day, and ISF can vary diurnally 2.
- Another approach is to use the insulin-to-carbohydrate ratio (ICR) to estimate ISF, with a linear regression analysis revealing that ISF can be estimated as 5.14 × ICR for any time of the day 2.
- Dynamic determination of basal insulin needs through linear regression and decomposition of previously dosed insulin and its effect on the patient's glycemia can also be used to estimate ISF 3.
- Additionally, a structural mathematical model of glucose-insulin relationships can be used to assess beta-cell function and insulin sensitivity, which can inform ISF determination 4.
Factors Influencing ISF
Several factors can influence ISF, including:
- Age 2
- Body mass index (BMI) 2
- Pubertal stage 2
- Diabetes duration 2
- Total daily insulin dose (TDD) 2
- Insulin-to-carbohydrate ratio (ICR) 2
Clinical Application
In clinical practice, ISF determination is crucial for calculating correction insulin doses and achieving optimal glycemic control 5, 2, 6. Continuous glucose monitoring (CGM) and ambulatory glucose profile (AGP) can provide valuable insights into glucose patterns and variability, informing ISF determination and insulin therapy adjustments 6.