Insulin/Diabetes Calculations Dr. Aipoalani St Lukes Endocrinology
Goals Describe various calculations for insulin dosing Understand importance of the total daily dose (TDD) of insulin Be able to calculate an insulin sensitivity factor Set up an insulin correction scale Calculate U-500 insulin starting doses
Preview TDD ( total daily dose ) ISF = 1500 / TDD ( glucose 150 ) / ISF = one time correction dose ICR = 450 / TDD = ( 1 unit insulin per g CHO ) 15 / ICR = insulin units per carb choice ( which is 15 g CHO ) U-500 dosing ( later )
Disclaimer/Cautions My calculations may not be exactly what you use Calculated doses are not exact and need further titration Some calculations work better (are more accurate) for type 1 diabetes than for type 2 diabetes This information is not really a guideline, but more of a way to guide insulin dosing
Why Is Knowledge of Insulin Important? Lots of people have diabetes and will get diabetes Insulin is required for treatment of type 1 diabetes Many patients will need insulin for type 2 diabetes Insulin doses that are not matched to each patient can cause: Poor DM control (complications) Hypoglycemia Scare the patient into non-compliance
Knowledge of Insulin Calculations Are Also Important Consult story Elderly patient in hospital type 1 diabetes frail/thin Glucose at night was ~450 Night/covering doctor was called: give 10 units of Novolog Patient subsequently had severe hypoglycemia (too much Novolog given)
Knowledge of Insulin Calculations Are Also Important Consult story I ll get back to this case later First, an overview of various types of insulin
Insulin Types
Starting Insulin in Diabetes type 2 Patient with type 2 diabetes: Failing oral DM therapy HbA1c not at goal Plan: start Insulin Tip: also stop sulfonylurea (glipizide, glyburide, glimipiride)
Starting Insulin in Diabetes type 2 Can start with basic dose (not calculated by body weight), such as: Lantus 10 units QHS Or Lantus 16 units QHS then titrate dose up as needed
Initial Weight-Based Dosing: DM2 Calculation: ( Weight in kg ) X ( Factor ) = # units of insulin (long-acting; give at bedtime) 0.2 0.3 0.4 HbA1c slightly above goal HbA1c moderately above goal HbA1c high, symptoms Example: ( 90 kg ) x ( 0.3 ) = 27 units Lantus QHS
Tip: 4 X 4 Remember: Keep increasing their Lantus/Levemir (long-acting) dose until glucose improved Tip: 2x2 or 4x4 dosing increase Tell patient, keep increasing dose by 2 or 4 units every few days until morning (pre-breakfast glucose ~100 (+/-)
Insulin Initiation in DM2 Summary When I start Lantus insulin for patient with type 2 diabetes: Start with Lantus (long-acting) insulin first Gain good glucose control by maximizing Lantus dose Later, add meal-time insulin (Novolog, Humalog, Apidra) and a correction scale
Total Daily Dose of Insulin (TDD) TDD = total amount of insulin a person takes in 24 hours (all types of insulin) The TDD is important since it is used in various insulin calculations
TDD: Examples DM1 DM2 Lantus 20 units QHS Novolog Breakfast: 4 units Lunch: 5 units Dinner: 4 units Lantus 60 units QHS Novolog 10 with meals (TID) Correction scale insulin: 10 units total TDD = 100 units Correction scale insulin: 5 units total TDD = 38 units
How to Calculate an Insulin Sensitivity Factor (ISF) ISF: how sensitive a person with diabetes is to insulin Estimates the point drop in glucose when 1 unit of rapidacting insulin is given (Novolog, Humalog) Mathematical rules for calculating ISF: Rule of 1500, 1700, 1800 I use 1500 ISF = 1500 / TDD
DM 1 patient TDD = 40 units ISF = 1500 / TDD ISF = 1500 / 40 ISF = 37 How to Calculate an Insulin Sensitivity Factor (ISF) 1 unit of Novolog will decrease their glucose by 37 points Examples:
DM 1 patient How to Calculate an Insulin Sensitivity Factor (ISF) Examples: DM 2 patient TDD = 40 units ISF = 1500 / TDD ISF = 1500 / 40 ISF = 37 1 unit of Novolog will decrease their glucose by 37 points TDD = 100 units ISF = 1500 / TDD ISF = 1500 / 100 ISF = 15 1 unit of Novolog will glucose decrease by 15 points
Insulin Sensitivity Factor (ISF) What does it mean? High ISF number = patient needs Lower Novolog correction doses Low ISF number = patient needs Higher Novolog correction doses
Insulin Sensitivity Factor: Comparison 1500 vs 1700 Comparison: TDD 40 units TDD 100 units Rule of 1500 37 15 Rule of 1700 42 17 Take home points: not a big difference between the calculated ISF between these rules option: can consider using Rule of 1700 if you want to be more gentle with setting up their correction scale, such as in sensitive DM type 1
ISF is Useful for 2 Reasons 1. Can be helpful in formulating an insulin correction scale 2. Can be used to give a one-time insulin correction dose for hyperglycemia
What is a Correction Scale? This is extra (rapid-acting) insulin such as Novolog/Humalog that is used to bring down a high blood sugar Usually want correction insulin to bring their glucose down to about 150 This correction dose is combined with their usual mealtime dose Meal dose Correction + = dose Total Meal dose
Use an ISF to make Correction Scale Calculate their ISF (insulin sensitivity factor) For example: 1500/50 = 30 Then, you can tell patient that for every 30 points above a glucose of 150, take 1 unit of Novolog; looks something like this written out <150 none extra 150-179 1 unit extra 180-209 2 units 210-239 3 units 240-269 4 units etc
Use ISF or TDD to pick one of these correction scales Low-dose Medium-dose High-dose 150-199: 1 unit 2 units 3 units 200-249: 2 units 4 units 6 units 250-299: 3 units 6 units 9 units 300-349: 4 units 8 units 12 units >350: 5 units 10 units 15 units ISF = 37-75 (TDD = 20-40) ISF = 15-37 (TDD = 40-100) ISF = 8-15 (TDD = 100-200)
Correction Scale Tips Try to keep the correction scale simple and easy to use I prefer not to have the scale go too high I prefer not to use Negative numbers Glucose: Units: 50-89 -1 unit 90-139 none extra 140-179 1 units 180-219 2 units 220-239 3 units 240-259 4 units 260-279 5 units 280-299 6 units Glucose: Units: 150-199 2 units 200-249 4 units 250-299 6 units 300-349 8 units 350-399 10 units 400-449 12 units 450-499 14 units 500-549 16 units 550-599 18 units 600-649 20 units 650-699 22 units 700 24 units
For blood sugar problems. Correction Scale Tips Focus should be to fix the core insulin regimen (Lantus and Novolog doses); not the correction scale Glucose: Units: Glucose: Units: 50-89 -1 unit 90-139 none extra 140-179 1 units 180-219 2 units 220-239 3 units 240-259 4 units 260-279 5 units 280-299 6 units Lantus or Novolog dose may be too HIGH Lantus or Novolog dose may be too LOW 150-199 2 units 200-249 4 units 250-299 6 units 300-349 8 units 350-399 10 units 400-449 12 units 450-499 14 units 500-549 16 units 550-599 18 units 600-649 20 units 650-699 22 units 700 24 units
320 Rule: Testing A Correction Scale Pt with DM2 TDD = 160 ISF = 1500/160 = 10 Medium-dose 150-199: 2 units 200-249: 4 units If glucose 320 and patient gives 8 units, is this correction scale dosed correctly? 250-299: 6 units 300-349: 8 units >350: 10 units
320 Rule: Testing A Correction Scale Pt with DM2 TDD = 160 ISF = 1500/160 = 10 Medium-dose 150-199: 2 units 200-249: 4 units If glucose 320 and patient gives 8 units, is this correction scale dosed correctly? Calculation: 250-299: 6 units 300-349: 8 units >350: 10 units 320 [ ISF x correction units ] = corrected glucose value 320 [ 10 x 8 ] = 240 glucose This correction scale is too low for patient (ideally want corrected glucose to be ~ 150 or so)
Correction Dose Calculation Let s go back to case of elderly patient with hyperglycemia Glucose 450 Doctor gave 10 units of Novolog then her blood sugar went down to 32 Why?
Correction Dose Calculation Let s go back to case of elderly patient with hyperglycemia Glucose 450 Doctor gave 10 units of Novolog then her blood sugar went down to 32 Why? TDD was only 20 units ISF (insulin sensitivity factor) = 1500 / 20 = 75 Based on her ISF, she only needed about 4 units of Novolog, not 10 that calculation is on the next slide
One-Time Correction Dose Calculation (Current glucose value - 150) / ISF = units of Novolog to give This the calculation that can help you give an appropriate correction dose to someone with high blood sugar Also helpful when you don t know patient well Example (frail hospital patient): (450-150) / 75 = 4 units of Novolog
One-Time Correction Dose Calculation (Current glucose value - 150) / ISF = units of Novolog to give Another example: Patient with DM 2 with higher TDD (high insulin resistance): DM2, TDD 150, ISF 10 If glucose 450 (450-150) / 10 = 30 units of Novolog, so would need much more insulin
Tip: Round Up their TDD Before Doing Other Calculations Patient with DM2 HbA1c 10% TDD = 80 units Before you do further calculations using this TDD, round it up because patient should actually be on MORE insulin Round up 10-20% depending on other factors Example: use TDD of 100 (not 80)
Meal-Time Insulin: Rule of 450 to get their Insulin to Carb Ratio Example; patient with type 1 diabetes: Calculate their total daily dose (TDD) Then use rule of 450 450 / TDD = insulin to carbohydrate ratio (ICR) Means you give 1 unit of Novolog per grams of CHO per meal Example: 450/45 = 10; so 1 unit Novolog/10 g CHO
Meal-Time Insulin: Dosing by Carb Choice For patient with type 2 diabetes; I like to use carb choice method One carb choice is a block of 15 grams of carb Step 1: Calculate their insulin to carb ratio, then convert as below: Step 2: 15 / ICR = units of insulin per carb choice
Meal-Time Insulin: Dosing by Carb Choice For patient with type 2 diabetes; I like to use carb choice method One carb choice is a block of 15 grams of carb Step 1: Calculate their insulin to carb ratio, then convert as below: Step 2: 15 / ICR = units of insulin per carb choice 2 Example: DM2, TDD 80, ICR = ~5; 2 15 / 5 = 3 units of insulin per carb choice with meals ( 3 units insulin ) x ( 4 carb choices ) = 12 units per meal
Meal-Time Insulin: Prescribing a Fixed dose that is based on a calculated Carb Ratio For example; patient with type 1 or type 2 diabetes who can t or does not want to carb count for their meals: Calculation is based on assuming they eat about 3 carb choices per meal; Step 1: calculate their TDD Step 2: calculate their ICR (insulin to carb ratio); 450 / TDD = ICR Step 3: convert to carb choice method; 15 / ICR = # units per carb choice Step 4: ( # units per carb choice ) x ( 3 carb choice per meal ) = their fixed dose of Novolog with meals
Starting Insulin in DM Type 1 Depends on various factors; coming off an insulin drip or not Usually: ( body wt in kg ) x ( 0.5 or 0.6 ) = TDD of insulin ( TDD ) x ( 0.5 ) = starting Lantus dose 1500 / TDD = ISF (insulin sensitivity factor) to set up Novolog correction scale 450 / TDD = ICR (carb ratio) to set Novolog mealtime insulin doses Then adjust as needed
Starting Insulin Pump: DM1 Here is one way Patient with DM1 on Lantus/Novolog regimen ( Current Lantus dose units ) x ( 0.8 ) / 24 = initial basal dose as Novolog in units/hour Calculate their current total daily dose (TDD); from their previous Lantus/Novolog 1500 / TDD = ISF (insulin sensitivity factor); program into pump (or can use rule of 1700 instead) 450 / TDD = ICR (carb ratio); program into pump
U-500 Insulin U-500 insulin is regular insulin that is 5 times more concentrated Very useful for patients with type 2 diabetes on high doses of insulin ( >200 units TDD) Better absorbed, fewer injections, improved glucose control (usually)
U-500 Insulin: Dosing Issues 2 ways to actually dose U-500 concentrated insulin: By UNITS using regular insulin syringe (my preference; outpatient) Or By VOLUME using TB syringe (inpatient use)
U-500 Insulin: Calculation 60 y/o female DM2 on Lantus and Novolog TDD = 220 units; HbA1c 9.6 lets start U-500 U-500 insulin is 5 times more concentrated, so divide TDD by 5; 220 / 5 = 44 concentrated U-500 units Initial starting U-500 dose should be reduced; so: ( 44 units ) X ( 0.7 ) = 30 units new U-500 TDD Split dose twice per day; 60% AM, 40% PM; so ( 30 units ) X ( 0.6 ) = 18 units AM U-500 units ( 30 units ) X ( 0.4 ) = 12 units PM U-500 units
U-500 Insulin: Calculation Or can use this table for reference Lantus & Novolog TDD (total daily dose): 200 units 220 240 260 280 Initial U-500 starting doses: 18 units AM, 10 units PM 18 units AM, 12 units PM 20 units AM, 14 units PM 22 units AM, 16 units PM 24 units AM, 16 units PM
U-500 Insulin: Titration PM dose controls AM glucose Increase U-500 PM dose by 2 units every 2 days until AM glucose ~100 AM dose control afternoon/pm glucose Increase U-500 AM dose by 2 units every 2 days until PM glucose ~ mid-100 s
U-500 Insulin: Benefits 60 y/o female DM2 on Lantus and Novolog On this U-500 regimen; HbA1c 6.8 Decreased injections from 5 per day to 2 per day No Lantus, No Novolog at meals, No correction scale insulin She has no hypoglycemia currently Patient happy with U-500 and doing well
U-500 Insulin: # of Injections Some providers like to use U-500 given 3 times per day I prefer twice a day with option of 3 times per day if needed
U-500 Insulin: Calculation The easy way on my Mac or ipad
Other insulin Calculations The easy way on my Mac or ipad
Insulin Split Concept Diabetes type 1 40% long-acting insulin 60% meal-time insulin Diabetes type 2 60% long-acting insulin 40% meal-time insulin These are not exact; depends on various factors Use these as a basic guide to see if patient is way off these percentages or not Consider adjusting insulin closer to these Some call this the basal-bolus ratio
Patient Examples/Cases #1 77 y/o female with DM2 many yrs metformin 500 mg twice a day Glyburide 10 mg twice a day A1c 9% Body wt: 178 lbs ( 80 kg ) Assuming you want to start insulin, what would you do?
Patient Examples/Cases #1 77 y/o female with DM2 many yrs metformin 500 mg twice a day Glyburide 10 mg twice a day A1c 9% Body wt: 178 lbs ( 80 kg ) I started Lantus insulin 16 units QHS ( 0.2 units/kg body wt ) Stopped the glyburide Glucose values & A1c improved
Patient Examples/Cases #2 56y/o male DM2 recent dx by PCP wks prior; outpatient PCP started on metformin 850 mg twice a day A1c 12% Body wt: 229 lbs (103 kg) Assuming you want to start insulin, what would you do?
Patient Examples/Cases #2 56y/o male DM2 recent dx by PCP wks prior; outpatient PCP started on metformin 850 mg twice a day A1c 12% Body wt: 229 lbs (103 kg) I started Lantus insulin 16 units QHS ( 0.15 units/kg body wt ) Several days later glucose values 80 s-100 s A1c 6.5%, 3 months later 0.2 units/kg = 20 units 0.3 units/kg = 30 units 0.4 units/kg = 40 units Example of why it s OK to underdose initially as long as you plan to increase doses at home; his current dose 1 year later Lantus 14 units QHS
Patient Examples/Cases #3 50 s y/o male with DM2 on insulin pump; A1c was ~7.5% 450/141 = 3 1500/141 = 11 TDD Approx 60% / 40% split
Patient Examples/Cases #4 21 y/o male with DM type 1 on insulin pump; A1c 6.2% TDD 450/33 = 14 1500/33 = 45 Insulin split % Basal rate
Summary TDD ISF = 1500/TDD (glucose - 150) / ISF = one time correction dose ICR = 450 / TDD = (1 unit insulin per g CHO) 15 / ICR = insulin units per carb choice Calculate their total daily dose (TDD) Calculate their insulin sensitivity factor (ISF) and carb ratio (ICR) Use an appropriate Novolog/Humalog correction scale Continually titrate Lantus and Novolog doses (individualize); or adjust insulin pump settings; also can consider 3 day CGM Check 2 hr postprandial glucose as a way to optimize meal-time insulin doses Recalculate these # s as their insulin doses change Consider U-500 insulin in (DM2) patients with TDD >200 units
Thank you TDD ISF = 1500 / TDD ( glucose 150 ) / ISF = one time correction dose ICR = 450 / TDD = ( 1 unit insulin per g CHO ) 15 / ICR = insulin units per carb choice ( which is 15 g CHO )