Insulin Sensitivity Factor (ISF)¶

What Is ISF?¶

Insulin Sensitivity Factor (ISF), also called Insulin Correction Factor (ICF), is the amount your blood glucose drops when you receive one unit of insulin. It's expressed as:

• mg/dL per unit (mg/dL/U)
• mmol/L per unit (mmol/L/U)

For example, an ISF of 50 mg/dL/U means that 1 unit of insulin will lower your glucose by 50 mg/dL (2.8 mmol/L).

Example Calculation¶

Why ISF Matters¶

ISF is one of the most critical settings in Trio because it determines:

1. SMB and Temp Basal Delivery: How much insulin is needed to bring high glucose back to target or keep glucose at target
2. Algorithm Calculations: Trio uses ISF every loop cycle to calculate optimal insulin delivery
3. Glucose Predictions: ISF affects how Trio predicts future glucose levels

How Trio Uses ISF¶

Like basal rates, Trio does not use your ISF verbatim. Instead, your scheduled ISF is modified dynamically based on:

1. Autosens Adjustments¶

When Autosens is enabled (which it is by default), Trio analyzes 8-24 hours of glucose data to calculate a Sensitivity Ratio. This ratio adjusts your ISF:

• Sensitivity Ratio > 1.0: You're more insulin-resistant → ISF is decreased (more insulin)
• Sensitivity Ratio < 1.0: You're more insulin-sensitive → ISF is increased (less insulin)
• Limits: Default range is 70-120% (controlled by Autosens Min/Max settings)

Example:

2. Dynamic ISF (Optional)¶

Dynamic ISF is a more aggressive way to adjust your ISF based on current glucose and/or historical insulin dosing:

• Requires: 7 days of TDD data with 85% coverage (minimum 1,715 data points)
• Types: Logarithmic (default) or Sigmoid
• Output: Dynamic Ratio that replaces the Autosens Ratio each loop cycle
• Temporary: The adjustment changes every loop cycle; it's not a permanent ISF change

Key Parameters:

• Adjustment Factor:
  • Sigmoid: Adjustment Factor controls how aggressively ISF changes. Learn more about how changes to Sigmoid Adjustment Factor influences ISF adjustments here. The default for Sigmoid Adjustment Factor is 50%.
  • Logarithmic: Controls what ISF is used at which glucose. It should be manually set to approximately \(0.02 \times TDD\). Learn more about how changing Adjustment Factor influences Logarithmic dynamic ISF here.
• Autosens Maximum: Controls the upper limit of the autosens ratio (default: 120%)
• Autosens Minimum: Controls the lower limit of the autosens ratio (default: 70%)
• Weighted Average of TDD: Blends recent (24h) and historical (10-day) insulin use (default: 35%)

Dynamic ISF is designed to make your ISF more aggressive (lower) when glucose is high and less aggressive (higher) when glucose is near target.

Time-Based ISF Schedules¶

Your insulin sensitivity varies throughout the day due to hormones, activity, and circadian rhythms. Trio supports time-based ISF schedules:

• Time slots in 30-minute increments
• Maximum of 48 entries (covering 24 hours)
• First entry must start at 00:00 (midnight)
• Each ISF applies from its start time until the next entry

Example ISF Schedule:

ISF Value Ranges¶

• Minimum: 9 mg/dL/U (0.5 mmol/L/U)
• Maximum: 540 mg/dL/U (30 mmol/L/U)
• Default: 200 mg/dL/U (11.1 mmol/L/U)
• Step: 1 mg/dL/U (0.1 mmol/L/U)

Testing and Adjusting Your ISF¶

Starting Point¶

If you're coming from pump therapy, you can transfer your pump's ISF as a starting point. However, be prepared to adjust it based on Trio's behavior.

Testing Method¶

To test if your ISF is accurate:

1. Choose a testing time: When you're "stuck" above target (around 150 mg/dL or 8.3 mmol/L) or by bringing yourself to a higher glucose with glucose tabs
2. Prepare Trio for testing: Set Max IOB to 0 (Optional: Set Autosens Max and Min to 100% to avoid Autosens adjustments)
3. Give a correction bolus based on your current ISF
   • To determine your testing dose, follow the formula \(\frac{Current\ Glucose - Target\ Glucose}{ISF}\)
4. Wait 4 hours without eating or exercising
5. Evaluate the result:
   • Still above target after 4 hours: ISF is too high (too conservative) → DECREASE the ISF value
   • Below target after 4 hours: ISF is too low (too aggressive) → INCREASE the ISF value
   • At target after 4 hours: ISF is accurate
6. Return Max IOB to your previous setting after you've completed the test

Relationship to Other Settings¶

ISF interacts with many Trio settings:

Autosens Integration¶

• Autosens Min/Max: Limits how much Autosens can adjust your ISF (default: 70-120%)
• Sensitivity Ratio: Applied to ISF and basal rates simultaneously

Dynamic ISF Integration¶

• Replaces Autosens: When Dynamic ISF is enabled, it calculates a Dynamic Ratio instead of using the Autosens Ratio
• Bounded by Autosens Limits: Dynamic Ratio is still constrained by Autosens Min/Max settings
• Affects Basal (optional): When "Adjust Basal" is enabled, Dynamic Ratio also modifies the baseline basal rate
• **Learn how your Profile ISF is used in Dynamic ISF by reviewing the page on Using Dynamic ISF

Temp Target Behavior (when enabled)¶

• High Temp Targets (>100 mg/dL): Increases effective ISF (less aggressive insulin delivery)
• Low Temp Targets (<100 mg/dL): Decreases effective ISF (more aggressive insulin delivery)
• Half Basal Exercise Target: Default 160 mg/dL; affects ISF scaling during exercise targets
• Temp Target Behavior settings will replace the Autosens or Dynamic Ratio calculations when enabled.

Sensitivity Target Behavior¶

• Adjusts target glucose based on the Sensitivity Ratio calculated by the algorithm
• Sensitivity Raises Target Increases your target glucose when Sensitivity Ratio is calculated less than 100%.
• Resistance Lowers Target decreases your target glucose when Sensitivity Ratio is calculated greater than 100%.

Bolus Calculator¶

ISF is used in the bolus calculator formula:

Carbs on Board (COB) Calculations¶

ISF is used to determine how quickly carbs are absorbed in your body and how fast Trio reduces the COB amount.

• ISF is used to determine your Carb Sensitivity Factor (CSF)
  • Formula: \(CSF=\frac{Carb\ Ratio}{\mathit{IS}\mathit{F}}\)
  • CSF shows how much 1g of carbohydrate will raise your glucose
• Carb Sensitivity Factor is used to determine how many carbs have been absorbed during that loop cycle
  • Formula: \(Increase\ in\ glucose \times CSF\)
  • Your COB will be reduced by this amount*

*If no change is indicated in your glucose readings, your Min 5m Carb Impact setting will be used for COB determination

Common ISF Mistakes¶

1. ISF Too Low (Too Aggressive)¶

Symptoms:

• Frequent hypoglycemia after corrections
• Rollercoaster patterns (high → over-correction → low → high)
• Excessive SMB delivery resulting in lows

Solution:

• Test your ISF
• Autosens or Sigmoid Dynamic ISF: Increase your profile ISF value (make it less aggressive)
• Logarithmic Dynamic ISF: Re-evaluate your Adjustment Factor and other Dynamic settings using the desmos graphs

2. ISF Too High (Too Conservative)¶

Symptoms:

• Persistent high glucose despite corrections
• Slow return to target
• Insufficient SMB delivery

Solution:

• Test your ISF
• Autosens or Sigmoid Dynamic ISF: Decrease your profile ISF value (make it more aggressive)
• Logarithmic Dynamic ISF: Re-evaluate your Adjustment Factor and other Dynamic Settings using the desmos graphs

3. Ignoring Time-of-Day Variations¶

Symptoms: - Good control at some times of day, poor at others - Dawn phenomenon not adequately addressed

Solution: Set different ISF values for different times of day based on need

Best Practices¶

1. Start conservatively: Begin with a higher (less aggressive) ISF and adjust downward if needed
2. Make small changes: Adjust by 5-10% at a time
3. Wait between changes: Give each adjustment 2-3 days to see the full effect
4. Test systematically: Test one time period at a time
5. Consider patterns: Look for consistent trends over multiple days, not single events
6. Monitor Autosens Ratio: Watching how your Autosens Ratio changes or doesn't change can indicate an issue with your Dynamic ISF settings
7. Work with your healthcare provider: Especially when making significant changes

Summary¶

ISF is a foundational setting that determines how much insulin is needed to correct high glucose. Getting your ISF right is crucial for Trio to function effectively. While Trio adjusts your ISF dynamically through Autosens or Dynamic ISF, having accurate baseline ISF values ensures:

• Safe and effective corrections
• Appropriate SMB delivery
• Smooth glucose control without rollercoasters
• Effective algorithm predictions and decisions

Take the time to test and refine your ISF carefully. It's one of the most important settings for successful automated insulin delivery.