Insulin Formulas

The insulin start formulae below may be based on basal bolus insulin therapy (BBIT at http://bbit.ca/ ), Diabetes Canada Guidelines or accepted practice. 

Basal Insulin Start

When basal insulin is added to non-insulin antihyperglycemic agents consider:

Diabetes Canada Guidelines: 10 units to start (individualized)

BBIT Guidelines: 0.1 to 0.2 units/kg = units basal insulin 

  • E.g. 100 kg X 0.1 or 0.2 = 10-20 units starting basal dose 100 kg client
  • Tip: Take weight in kg and move decimal to the left for the LOWEST starting dose.
    Double that number for the highest starting dose.
  • Actual needs can be significantly higher, particularly in those who are resistant, however start conservatively.

Bolus Insulin Start

Diabetes Canada Guidelines: 2 - 4 units per meal

BBIT Guidelines: 0.05 - 0.1 units / kg = units per meal 

  • E.g. 100 kg X 0.05 or 0.1 = 5 -10 units
  • Tip: Take weight in kg and move decimal to the left for the HIGHEST starting bolus dose per meal. Cut this in half for the lowest starting bolus dose per meal. 
  • When to start bolus: If on > 0.5 units basal insulin per kg and not at target, consider adding bolus soon (consider A1c, age, complexity, etc).
  • Actual bolus needs can be significantly higher, particularly in those who are resistant, however start conservatively. 

Basal & Bolus Start 

  • Starting TDD = 0.5 - 1.0 units/kg/day
    (0.3 - 0.5 u/kg/day if more sensitive to insulin; 0.5 - 1.0 u/kg/day if more insulin resistant)
    • Daily basal insulin =  50% of TDD 
    • Daily bolus insulin =  50% of TDD  (distributed amongst 3 meals)
    • Or, if mixed insulin (e.g. 30/70) loosely 2/3 of TDD premix at breakfast and 1/3 at supper.
  • Tip: If resistant consider this shortcut:
    • half the weight in kg = total daily basal units
    • half the weight in kg = total daily bolus units (distribute over 3 meals)
  • Example for 100 kg resistant patient
    • 50 units basal
    • 50 units bolus
      (50 / 3 meals = 16 units per meal but preferable to individualize.
      e.g. if breakfast is small and supper large, then distribute it proportionately)

Assessing % Basal in BBIT

  • Total daily units basal / total daily units all insulin x 100 = % of insulin as basal
    e.g. 45 units basal for the day / 90 units TDD x 100 = 50% of insulin as basal
  • For most people, approximately 40-60% of their total daily dose of insulin (TDD) is basal insulin. This split varies for those on partial-closed-loop insulin pumps due to algorithms. For those with low carbohydrate diets, expect a higher % basal.

Insulin Sensitivity Factor (ISF) or Correction Dose 

To create an Insulin Sensitivity Factor (ISF) for RAPID insulin:

  • 100/TDD = number of mmol/L 1 unit rapid will lower glucose level.
    E.g. 100/50 units TDD = 2
    1 unit will drop glucose by about 2 mmol/L

To create an Insulin Sensitivity Factor (ISF) for REGULAR insulin:

  • 83/TDD = number of mmol/L 1 unit regular insulin will lower glucose level.
    E.g. 83/30 units TDD = about 3.
    1 unit will lower glucose by about 3 mmol/L

To use an ISF:

  • (Current Blood Glucose – target) / ISF= units to give to correct high glucose reading
  • e.g. If current BG 13 mmol/L , ISF is 2 and target is 7 mmol then:
    13 mmol/L - 7 mmol/L  = 6 / ISF 2 = 3 units for correction 

To create correction/ISF tables:

Insulin to Carb Ratio (ICR)

  • Method 1: Divide grams of usable carbohydrate eaten for a meal by bolus dose (units) per same meal
    e.g. 50 g carb eaten / 5 units rapid = ICR 10
    Therefore, 1 unit of bolus insulin is given for every 10 g usable carb eaten 

  • Method 2: The 500 rule (500/TDD)
    e.g. 500 / Total Daily Dose of insulin of 50 units = ICR 10
    Therefore, 1 unit of bolus insulin is given for every 10 g usable carb eaten
Adjusting ICR:
  • If glucose readings are too high after meal, consider reducing the ICR number. Have the patient work through an example to see if the change is appropriate. 
    • ICR = 20 consider new ICR = 15
    • ICR = 15, consider new ICR = 12
    • ICR = 12, consider new ICR = 10
    • ICR=10 consider new  ICR = 9 or 8
    • ICR = 9, consider new ICR = 8
  • If glucose readings are low after meal, consider increasing the ICR number. Have the patient work through an example to see if the change is appropriate.
    • ICR = 8, consider new ICR = 9 or 10
    • ICR = 10 consider new ICR = 12
    • ICR = 12 consider new ICR = 15
    • ICR = 15 consider new ICR = 20   

  • Another option, if pattern of highs at a meal, take the units of correction dose and add to the previous meals' bolus dose.
    • e.g. Before bedtime snack patient needs 3 units of correction dose most days as high readings. Add 3 units to the supper meal bolus dose to prevent the highs.
    • As an example, if ICR = 10, usual supper 60 g carb, usual meal bolus (not correction) 6 units then the new ratio is determined by Method 1: 60 g carb / 9 units (past 6 units + 3 units new to prevent highs at supper) = ICR 7 (approx)