Carbohydrate Count in Insulin Dosing

Aka: Carbohydrate Count in Insulin Dosing, Insulin Adjustment with Carbohydrate Counting

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II. Management: Step 1a - Determine Carbohydrate to Insulin ratio

  1. Determine total Insulin used per day
    1. Option 1: Known dose from multiple daily doses or Insulin Pump
    2. Option 2: Calculate based on patient weight
      1. Type I: Total daily Insulin (TDI)
        1. TDI = WtKg x 0.1 to 0.3 units/kg (start low)
      2. Type I: Total basal dose (TBD)
        1. TBD = WtKg x 0.2
        2. TBD = 0.4 x Total Daily Insulin (TDI)
      3. Type II: Total daily Insulin (TDI)
        1. TDI = WtKg x 0.3 units/kg: Underweight, advance age, Dialysis
        2. TDI = WtKg x 0.4 units/kg: Normal weight
        3. TDI = WtKg x 0.5 units/kg: Overweight
        4. TDI = WtKg x 0.6 units/kg: Obese, steroid use, high Insulin Resistance
    3. Option 3: Simple Carbohydrate based-method (below in Step Ib)
  2. Plan to split the Basal insulin and Bolus Insulin evenly (50% to each)
  3. Calculate Insulin to Carbohydrate ratio or ICR (g carb per one unit Insulin)
    1. Short-acting rapid Insulin: Humalog (Lispro)
      1. Ratio (ICR) = 500 / (total daily Insulin or TDI dose)
    2. Short-Acting Insulin: Regular
      1. Ratio (ICR) = 450 / (total daily Insulin dose)
    3. Other formulas
      1. Ratio (ICR) = 100 / (total basal dose or TBD)
  4. Calculate correction factor (CF)
    1. Blood Glucose drop expected per unit of Insulin (using the Insulin-carb ratio or ICR above)
    2. Formula
      1. CF = ICR * 4.5
    3. For example
      1. Given Insulin to Carbohydrate ratio of 6 g carb/unit
      2. Blood Glucose would correct 27 mg/dl with one unit Insulin
  5. Interpretation
    1. Ratio is Carbohydrate grams covered by 1 unit Insulin
    2. Type I Diabetes
      1. One unit per Carbohydrate (15 grams) is typical
      2. Effect of one unit Insulin on Glucose lowering
        1. Typically 1 Unit Bolus Insulin lowers Glucose 20-60 mg/dl
        2. Estimate: 1800/(daily Insulin dose)
  6. Example
    1. Type I Diabetes patient weighs 110 kg and uses ~35 total units of Insulin per day (0.3 units/kg)
    2. One unit Insulin covers 500/35 or 14 g Carbohydrates
    3. One unit Insulin would be expected to lower Glucose 1800/35 or 50 mg/dl (in Type I Diabetes Mellitus)
    4. Lantus: Takes 18 units of Lantus per day
    5. Lispro: Takes 16 units total (4 units for each of 3 meals and 2 units for each of 2 snacks)

III. Management: Step 1b - Alternative to Step 1a (Simple Method)

  1. Dietician directs grams of Carbohydrate per meal
    1. Estimate Daily Energy Allowance (calories)
    2. Estimate percentage of calories in diet (50-60%)
    3. Calories per gram of Carbohydrate = 4
    4. Calculate total daily Carbohydrate grams
      1. Daily Carbs (grams) = (Total Calories x 0.5) / 4
      2. Example = (1800 x 0.5)/4 = 225 Carbohydrate grams
    5. Spread out Carbohydrate grams across meals
      1. Example: 70 grams per meal, and two 20 gram snacks
  2. Choose Carbohydrate servings to meet needs
    1. Each serving contains 12-15 grams Carbohydrate
    2. Choose servings from 3 groups
      1. Breads and starches
      2. Fruit
      3. Milk
      4. Vegetables are not counted

IV. Management: Step 2 - Predict Carbohydrate effect on Serum Glucose

  1. Glucose rises at constant rate per gram Carbohydrate
    1. Weight 100 lbs: 1g carb raises Glucose 5 points
    2. Weight 150 lbs: 1g carb raises Glucose 4 points
    3. Weight 200 lbs: 1g carb raises Glucose 3 points
  2. Other modifiers of Carbohydrate effect on Serum Glucose
    1. Glycemic Index
    2. Percentage of food from Protein and fat

V. Management: Step 3 - Count Carbohydrates

  1. Indications
    1. Estimate Insulin needs per meal
    2. Plan meal to raise Glucose to certain level
  2. Techniques
    1. Food labels (use grams of Carbohydrate per serving)
    2. Food tables (e.g. cookbooks, references)
    3. Food weight
      1. Determine Carb Factor for particular food
        1. Percentage of given food from Carbohydrate
      2. Weigh food on gram scale
      3. Carbohydrate grams = (food weight) x (carb factor)

VI. Management: Step 5 - Summary: Combining Insulin protocols

  1. Basal insulin (Maintenance, covers between meals and ovenight)
    1. Once daily: Lantus
    2. Twice daily: Levemir, NPH Insulin
  2. Bolus Insulin (pre-meal Insulin, covers post-meal Blood Sugars)
    1. Units per Carbohydrate of planned meal AND
    2. Units of Correctional Insulin Dosing based on Blood Sugars over 149 before the meal
  3. Example
    1. A 70 kg man with Type II Diabetes Mellitus
    2. Insulin Glargine (Lantus)
      1. Uses 14 units per day at dinner
    3. InsulinHumalog (Lispro) with coverage
      1. Uses 1 unit per Carbohydrate PLUS 1 unit per 50 over 150
      2. Blood Sugar of 200 at lunch and having prepared a 4 Carbohydrate meal
      3. Takes a total of 6 units: 4 units (4 carbs) plus an additional 2 units (for Blood Sugar of 200)

VII. References

  1. Smith (2018) Am Fam Physician 98(3): 154-62 [PubMed]

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