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INSULIN CALCULATIONS CHEAT SHEET
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Note: TDD=Total daily Dose ICR=Insulin to Carbohydrate Ratio ISF=Insulin Sensitivity Factor ICR=Insulin Correction Ratio
Insulin Calculation Example How to understand ICR: 500/TDD (basal and bolus combined)
One of your patients with type 2 diabetes is on 20 units of Toujeo (concentrated glargine) once daily and 10 units of FIASP (aspart) three times a day with each meal. The patients total daily dose is 20+10+10+10=50 so 500/50= 1 unit per 10 grams of carbohydrate
This equation assumes that an average person consumes 500 grams of carbohydrate per day. The higher the TDD the higher the insulin resistance. Higher insulin resistance means the patient needs more insulin for every carbohydrate they consume. For the CDE™ exam use this equation. In real life I don’t find this equation very accurate. 500 grams of carbohydrate is equal to 33 slices of bread! Please see the two alternate ways of calculating insulin to carb ratio at the end ISF or ICR: If on rapid acting insulin: 100/TDD If on regular or fast acting insulin: 83/TDD
Your patient is on Apidra (glulisine) 20 units three times a day and Xultophy (degludec/liraglutide) 40 units/1.44mg once daily. 20+20+20+40=100 so 100/100= 1 mmol/L drop for every 1 unit of rapid insulin
These equations were originally developed by Dr Paul Davidson in Atlanta, Georgia based on his experience with treating patients with diabetes. For regular insulin he developed the 83 rule. Because the blood sugar tends to drop faster and farther on rapid acting insulins, like Humalog (lispro) and Novorapid (aspart), the 100 rule is used. These equations predict how much one unit of insulin drops blood sugar.
Your patient is on Humulin R (regular insulin) 7 units three times a day with each meal and 20 units of Toujeo (concentrated glargine) once daily. 7+7+7+20=41. 83/41= 2 mmol/L drop for every 1 unit of regular insulin.
Switching from BID (twice daily) basal insulin dosing = reduce dose by 20%
You have a patient who takes 50 units of NPH insulin twice daily. You switch him to Lantus (glargine) once daily. So 50+50=100 x 0.8 = 80 units of Lantus (glargine) once daily
This was originally part of the Lantus monograph. When switching to twice daily NPH to once daily Lantus, researchers usually reduced the dose by 20%. Since then it has become a general insulin adjustment rule to reduce the dose by 20% when switching from twice daily basal insulin to once daily basal insulin. In my own practice I have found that if you switch insulin and the patient experiences hypoglycemia then you lose the patient’s trust and they are less receptive to your suggestions. So, it’s better to be safe than sorry Switching from multiple daily injections to continuous subcutaneous infusion = reduce TDD by 25% then split 60/ bolus/basal
You have a patient who is switching onto an insulin pump. Currently she is on Humalog 5 units three times a day with meals and Basalglar (glargine) 85 units once daily. So 5+5+5=85= 100 TDD. 100 x 0.75= 75 units. 75 x 0.6= 45 bolus so 45/3= 15 units bolus with each meal and 75 x 0.4= 30 units of basal NOTE: Insulin pumps only use rapid insulin
A normal pancreas secretes insulin monomers (the active form of insulin) throughout the day and in response to meals. Basal insulin does not simulate normal pancreas secretion as well as an insulin pump. After injection, basal insulin forms a depot in the subcutaneous layer of the skin where it slowly disassociates into monomers. Some of the basal insulin is degraded as it sits and disassociates. Insulin pumps simulate normal pancreas secretion better by pumping small amounts of rapid acting insulin that disassociate rapidly into monomers. So, you use a lower dose with an insulin pump as the insulin is used more efficiently. A1c to average blood glucose= ((A1c-6) x2) + 6 = average BG in mmol/L
You have a patient who has an A1c of 10%. His average BG is: ((10-6) x 2) +6= average 14 mmol/L
There is usually a question on the exam where a patient says his A1c is X% and asks what is his average mmol/L. Here is an easy formula to learn for the exam and in real life. Basal insulin start= Start with 10 units once daily
10 units is the suggested starting dose for basal insulin starts. You can choose a lower dose if the patient is elderly or patient’s body weight is normal to low
See Appendix 9 on pg S 317 on the 2018 Diabetes Canada guidelines for more information
Bolus insulin start= Start with 2-4 units
Start with 2-4 units at one meal of the day. You do not need to start with all three meals. The Stepwise study showed that patients get the most benefit with the first bolus dose at a meal and get less benefit with each additional bolus dose at meals.
See Appendix 9 on pg S 317 on the 2018 Diabetes Canada guidelines for more information
Alternate Method for ICR based on pre and post prandial blood sugar readings. Use the Beyond the Basics guide to calculate carbohydrate content in grams.
Below is your patient’s food diary and blood glucose log: You need to calculate the ICR used and then compare Pre-breakfast=6.8 Had 2 slices of white toast and a glass of diet coke. Took 5 units of Humalog. 2-hour PC BG= 3.
2 white toast = 30 carbs. Diet coke = 0 carbs. Total carbs= 30/5 Humalog= 1:6 ICR. Pt went low so too much Pre-lunch= 5.2 Had 2 cups of salad, 2 medium apples and 3 boiled eggs. Took 2 units of Humalog. 2 hr PC BG= 7.
Salad= 0 carbs, 2 medium apples= 3 2 gram of carbs, 3 boiled egg= 0 carbs. Total carbs= 30/2 Humalog= 1:1 6 ICR. Pt was on target after meal, so this is a good ICR Pre-supper= 5.8 Had a 6 oz steak, 1 cup of mashed potatoes, 1 cup of salad, 1 cup of boiled rice and a cup of unsweetened tea. Took 5 units of Humalog. 2 hr PC BG=
Steak=0 carbs, mashed potatoes= 57 gram, salad= 0 carbs, boiled rice= 3 9 gram, tea= 0 gram. Total carbs= 96 grams/ 5 Humalog= 1:20 ICR. Pt was above target so not enough. Comparing all the different ICR the patient used it seems that the 1:15 ratio is best. For more questions please check out the free quizzes I have on my website.
